Heat capacity is the ability to absorb some amount of heat during heating or release it during cooling. The heat capacity of a body is the ratio of the infinitesimal amount of heat that the body receives to the corresponding increase in its temperature indicators. The value is measured in J/K. In practice, a slightly different value is used - specific heat capacity.
Definition
What does specific heat capacity mean? This is a quantity related to a unit amount of a substance. Accordingly, the amount of a substance can be measured in cubic meters, kilograms or even moles. What does this depend on? In physics, heat capacity depends directly on which quantitative unit it belongs to, which means that they distinguish between molar, mass and volumetric heat capacity. In the construction industry you won't encounter molar measurements, but you will encounter others all the time.
What affects specific heat capacity?
You know what heat capacity is, but what values affect the indicator is not yet clear. The value of specific heat capacity is directly affected by several components: temperature of the substance, pressure and other thermodynamic characteristics.
As the temperature of a product increases, its specific heat capacity increases, but certain substances have a completely nonlinear curve in this dependence. For example, with an increase in temperature indicators from zero to thirty-seven degrees, the specific heat capacity of water begins to decrease, and if the limit is between thirty-seven and one hundred degrees, then the indicator, on the contrary, will increase.
It is worth noting that the parameter also depends on how the thermodynamic characteristics of the product (pressure, volume, etc.) are allowed to change. For example, the specific heat capacity at stable pressure and at stable volume will be different.
How to calculate the parameter?
Are you interested in what the heat capacity is? The calculation formula is as follows: C=Q/(m·ΔT). What kind of meanings are these? Q is the amount of heat that the product receives when heated (or released by the product during cooling). m is the mass of the product, and ΔT is the difference between the final and initial temperatures of the product. Below is a table of the heat capacity of some materials.
What can you say about calculating heat capacity?
Calculating heat capacity is not the easiest task, especially if you use exclusively thermodynamic methods; it is impossible to do it more precisely. Therefore, physicists use methods of statistical physics or knowledge of the microstructure of products. How to make calculations for gas? The heat capacity of a gas is calculated by calculating the average energy of thermal motion of individual molecules in a substance. Molecular movements can be translational or rotational, and inside a molecule there can be a whole atom or a vibration of atoms. Classical statistics says that for each degree of freedom of rotational and translational motions there is a molar value that is equal to R/2, and for each vibrational degree of freedom the value is equal to R. This rule is also called the law of equipartition.
In this case, a particle of monatomic gas has only three translational degrees of freedom, and therefore its heat capacity should be equal to 3R/2, which is in excellent agreement with experiment. Each molecule of a diatomic gas is distinguished by three translational, two rotational and one vibrational degrees of freedom, which means that the law of equipartition will be equal to 7R/2, and experience has shown that the heat capacity of a mole of diatomic gas at ordinary temperature is 5R/2. Why was there such a discrepancy between the theories? Everything is connected with the fact that when establishing heat capacity, it will be necessary to take into account various quantum effects, in other words, to use quantum statistics. As you can see, heat capacity is a rather complex concept.
Quantum mechanics says that any system of particles that vibrates or rotates, including a gas molecule, can have certain discrete energy values. If the energy of thermal motion in the installed system is insufficient to excite oscillations of the required frequency, then these oscillations do not contribute to the heat capacity of the system.
In solids, the thermal motion of atoms is weak vibrations near certain equilibrium positions, this applies to the nodes of the crystal lattice. An atom has three vibrational degrees of freedom and, according to the law, the molar heat capacity of a solid body is equal to 3nR, where n is the number of atoms present in the molecule. In practice, this value is the limit to which the heat capacity of a body tends at high temperatures. The value is achieved with normal temperature changes for many elements, this applies to metals, as well as simple compounds. The heat capacity of lead and other substances is also determined.
What about low temperatures?
We already know what heat capacity is, but if we talk about low temperatures, how will the value be calculated then? If we are talking about low temperatures, then the heat capacity of a solid body then turns out to be proportional T 3 or the so-called Debye's law of heat capacity. The main criterion for distinguishing high temperatures from low ones is the usual comparison of them with a parameter characteristic of a particular substance - this can be the characteristic or Debye temperature q D. The presented value is established by the vibration spectrum of atoms in the product and significantly depends on the crystal structure.
In metals, conduction electrons make a certain contribution to the heat capacity. This part of the heat capacity is calculated using Fermi-Dirac statistics, which takes electrons into account. The electronic heat capacity of a metal, which is proportional to the usual heat capacity, is a relatively small value, and it contributes to the heat capacity of the metal only at temperatures close to absolute zero. Then the lattice heat capacity becomes very small and can be neglected.
Mass heat capacity
Mass specific heat capacity is the amount of heat that is required to be added to a unit mass of a substance in order to heat the product by a unit temperature. This quantity is designated by the letter C and is measured in joules divided by kilogram per kelvin - J/(kg K). That's all for mass heat capacity.
What is volumetric heat capacity?
Volumetric heat capacity is a certain amount of heat that needs to be supplied to a unit volume of a product in order to heat it per unit temperature. This indicator is measured in joules divided per cubic meter per kelvin or J/(m³·K). In many construction reference books, it is the mass specific heat capacity in the work that is considered.
Practical application of heat capacity in the construction industry
Many heat-intensive materials are actively used in the construction of heat-resistant walls. This is extremely important for houses characterized by periodic heating. For example, a stove. Heat-intensive products and walls built from them perfectly accumulate heat, store it during heating periods and gradually release heat after the system is turned off, thus allowing you to maintain an acceptable temperature throughout the day.
So, the more heat stored in the structure, the more comfortable and stable the temperature in the rooms will be.
It is worth noting that ordinary brick and concrete used in house construction have a significantly lower heat capacity than expanded polystyrene. If we take ecowool, it has three times more heat capacity than concrete. It should be noted that it is not for nothing that mass is present in the formula for calculating heat capacity. Thanks to the large, enormous mass of concrete or brick compared to ecowool, it allows the stone walls of structures to accumulate huge amounts of heat and smooth out all daily temperature fluctuations. Only the low mass of insulation in all frame houses, despite its good heat capacity, is the weakest area of all frame technologies. To solve this problem, impressive heat accumulators are installed in all houses. What is it? These are structural parts characterized by a large mass with a fairly good heat capacity.
Examples of heat accumulators in real life
What could it be? For example, some internal brick walls, a large stove or fireplace, concrete screeds.
Furniture in any house or apartment is an excellent heat accumulator, because plywood, chipboard and wood can actually store three times more heat per kilogram of weight than the notorious brick.
Are there any disadvantages to thermal accumulators? Of course, the main disadvantage of this approach is that the heat accumulator needs to be designed at the stage of creating a model of a frame house. This is due to the fact that it is heavy, and this will need to be taken into account when creating the foundation, and then imagine how this object will be integrated into the interior. It is worth saying that you will have to take into account not only mass, you will need to evaluate both characteristics in your work: mass and heat capacity. For example, if you use gold with an incredible weight of twenty tons per cubic meter as a heat accumulator, then the product will function as required only twenty-three percent better than a concrete cube that weighs two and a half tons.
Which substance is most suitable for a heat accumulator?
The best product for a heat accumulator is not concrete and brick! Copper, bronze and iron cope well with this task, but they are very heavy. Oddly enough, but the best heat accumulator is water! The liquid has an impressive heat capacity, the largest among substances available to us. Only the gases helium (5190 J/(kg K) and hydrogen (14300 J/(kg K)) have a greater heat capacity, but they are problematic to use in practice. If desired and necessary, see the table of the heat capacity of the substances you need.
(or heat transfer).
Specific heat capacity of a substance.
Heat capacity- this is the amount of heat absorbed by a body when heated by 1 degree.
The heat capacity of a body is indicated by a capital Latin letter WITH.
What does the heat capacity of a body depend on? First of all, from its mass. It is clear that heating, for example, 1 kilogram of water will require more heat than heating 200 grams.
What about the type of substance? Let's do an experiment. Let's take two identical vessels and, having poured water weighing 400 g into one of them, and vegetable oil weighing 400 g into the other, we will begin to heat them using identical burners. By observing the thermometer readings, we will see that the oil heats up quickly. To heat water and oil to the same temperature, the water must be heated longer. But the longer we heat the water, the more heat it receives from the burner.
Thus, heating the same mass of different substances to the same temperature requires different amounts of heat. The amount of heat required to heat a body and, therefore, its heat capacity depend on the type of substance of which the body is composed.
So, for example, to increase the temperature of water weighing 1 kg by 1°C, an amount of heat equal to 4200 J is required, and to heat the same mass of sunflower oil by 1°C, an amount of heat equal to 1700 J is required.
A physical quantity showing how much heat is required to heat 1 kg of a substance by 1 ºС is called specific heat capacity of this substance.
Each substance has its own specific heat capacity, which is denoted by the Latin letter c and measured in joules per kilogram degree (J/(kg °C)).
The specific heat capacity of the same substance in different states of aggregation (solid, liquid and gaseous) is different. For example, the specific heat capacity of water is 4200 J/(kg °C), and the specific heat capacity of ice is 2100 J/(kg °C); aluminum in the solid state has a specific heat capacity of 920 J/(kg - °C), and in the liquid state - 1080 J/(kg - °C).
Note that water has a very high specific heat capacity. Therefore, water in the seas and oceans, heating up in summer, absorbs a large amount of heat from the air. Thanks to this, in those places that are located near large bodies of water, summer is not as hot as in places far from the water.
Calculation of the amount of heat required to heat a body or released by it during cooling.
From the above it is clear that the amount of heat required to heat a body depends on the type of substance of which the body consists (i.e., its specific heat capacity) and on the mass of the body. It is also clear that the amount of heat depends on how many degrees we are going to increase the body temperature.
So, to determine the amount of heat required to heat a body or released by it during cooling, you need to multiply the specific heat capacity of the body by its mass and by the difference between its final and initial temperatures:
Q = cm (t 2 - t 1 ) ,
Where Q- amount of heat, c— specific heat capacity, m- body weight, t 1 — initial temperature, t 2 — final temperature.
When the body heats up t 2 > t 1 and therefore Q > 0 . When the body cools down t 2i< t 1 and therefore Q< 0 .
If the heat capacity of the entire body is known WITH, Q determined by the formula:
Q = C (t 2 - t 1 ) .
Physics and thermal phenomena is a fairly extensive section that is thoroughly studied in the school course. Not the last place in this theory is given to specific quantities. The first of these is specific heat capacity.
However, insufficient attention is usually paid to the interpretation of the word “specific”. Students simply remember it as a given. What does it mean?
If you look into Ozhegov’s dictionary, you can read that such a quantity is defined as a ratio. Moreover, it can be performed in relation to mass, volume or energy. All these quantities must be taken equal to one. Specific heat capacity is related to what?
To the product of mass and temperature. Moreover, their values must be equal to one. That is, the divisor will contain the number 1, but its dimension will combine kilogram and degree Celsius. This must be taken into account when formulating the definition of specific heat capacity, which is given a little below. There is also a formula from which it is clear that these two quantities are in the denominator.
What is it?
The specific heat capacity of a substance is introduced at the moment when the situation with its heating is considered. Without it, it is impossible to know how much heat (or energy) will be required for this process. And also calculate its value when the body cools. By the way, these two amounts of heat are equal to each other in modulus. But they have different signs. So, in the first case it is positive, because energy needs to be expended and it is transferred to the body. The second cooling situation gives a negative number because heat is released and the internal energy of the body decreases.
This physical quantity is denoted by the Latin letter c. It is defined as a certain amount of heat required to heat one kilogram of a substance by one degree. In a school physics course, this degree is the one taken on the Celsius scale.
How to count it?
If you want to know what the specific heat capacity is, the formula looks like this:
c = Q / (m * (t 2 - t 1)), where Q is the amount of heat, m is the mass of the substance, t 2 is the temperature that the body acquired as a result of heat exchange, t 1 is the initial temperature of the substance. This is formula number 1.
Based on this formula, the unit of measurement of this quantity in the international system of units (SI) turns out to be J/(kg*ºС).
How to find other quantities from this equality?
Firstly, the amount of heat. The formula will look like this: Q = c * m * (t 2 - t 1). Only it is necessary to substitute values in SI units. That is, mass in kilograms, temperature in degrees Celsius. This is formula number 2.
Secondly, the mass of a substance that cools or heats up. The formula for it will be: m = Q / (c * (t 2 - t 1)). This is formula number 3.
Thirdly, temperature change Δt = t 2 - t 1 = (Q / c * m). The sign “Δ” is read as “delta” and denotes a change in a quantity, in this case temperature. Formula No. 4.
Fourthly, the initial and final temperatures of the substance. The formulas valid for heating a substance look like this: t 1 = t 2 - (Q / c * m), t 2 = t 1 + (Q / c * m). These formulas are Nos. 5 and 6. If the problem is about cooling a substance, then the formulas are: t 1 = t 2 + (Q / c * m), t 2 = t 1 - (Q / c * m). These formulas are No. 7 and 8.
What meanings can it have?
It has been established experimentally what values it has for each specific substance. Therefore, a special specific heat capacity table has been created. Most often it contains data that is valid under normal conditions.
What is the laboratory work involved in measuring specific heat capacity?
In the school physics course it is defined for a solid body. Moreover, its heat capacity is calculated by comparison with that which is known. The easiest way to do this is with water.
During the work, it is necessary to measure the initial temperatures of water and a heated solid. Then lower it into the liquid and wait for thermal equilibrium. The entire experiment is carried out in a calorimeter, so energy losses can be neglected.
Then you need to write down the formula for the amount of heat that water receives when heated from a solid. The second expression describes the energy that a body gives off when cooling. These two values are equal. Through mathematical calculations, it remains to determine the specific heat capacity of the substance that makes up the solid.
Most often it is proposed to compare it with table values in order to try to guess what substance the body under study is made of.
Task No. 1
Condition. The temperature of the metal varies from 20 to 24 degrees Celsius. At the same time, its internal energy increased by 152 J. What is the specific heat of the metal if its mass is 100 grams?
Solution. To find the answer, you will need to use the formula written under number 1. All the quantities necessary for the calculations are there. Just first you need to convert the mass into kilograms, otherwise the answer will be wrong. Because all quantities must be those accepted in SI.
There are 1000 grams in one kilogram. This means that 100 grams must be divided by 1000, you get 0.1 kilograms.
Substitution of all quantities gives the following expression: c = 152 / (0.1 * (24 - 20)). The calculations are not particularly difficult. The result of all actions is the number 380.
Answer: s = 380 J/(kg * ºС).
Problem No. 2
Condition. Determine the final temperature to which water with a volume of 5 liters will cool if it was taken at 100 ºС and released 1680 kJ of heat into the environment.
Solution. It’s worth starting with the fact that energy is given in a non-systemic unit. Kilojoules need to be converted to joules: 1680 kJ = 1680000 J.
To find the answer, you need to use formula number 8. However, mass appears in it, and in the problem it is unknown. But the volume of liquid is given. This means that we can use the formula known as m = ρ * V. The density of water is 1000 kg/m3. But here the volume will need to be substituted in cubic meters. To convert them from liters, you need to divide by 1000. Thus, the volume of water is 0.005 m 3.
Substituting the values into the mass formula gives the following expression: 1000 * 0.005 = 5 kg. You will need to look up the specific heat capacity in the table. Now you can move on to formula 8: t 2 = 100 + (1680000 / 4200 * 5).
The first action is to multiply: 4200 * 5. The result is 21000. The second is division. 1680000: 21000 = 80. The last one is subtraction: 100 - 80 = 20.
Answer. t 2 = 20 ºС.
Problem No. 3
Condition. There is a beaker weighing 100 g. 50 g of water is poured into it. The initial temperature of the water with the glass is 0 degrees Celsius. How much heat is required to bring water to a boil?
Solution. A good place to start is by introducing a suitable designation. Let the data related to the glass have an index of 1, and for water - an index of 2. In the table, you need to find the specific heat capacities. The beaker is made of laboratory glass, so its value c 1 = 840 J/ (kg * ºC). The data for water is: c 2 = 4200 J/ (kg * ºС).
Their masses are given in grams. You need to convert them to kilograms. The masses of these substances will be designated as follows: m 1 = 0.1 kg, m 2 = 0.05 kg.
The initial temperature is given: t 1 = 0 ºС. It is known about the final value that it corresponds to the point at which water boils. This is t 2 = 100 ºС.
Since the glass heats up along with the water, the required amount of heat will be the sum of two. The first, which is required to heat the glass (Q 1), and the second, which is used to heat the water (Q 2). To express them you will need a second formula. It must be written down twice with different indices, and then sum them up.
It turns out that Q = c 1 * m 1 * (t 2 - t 1) + c 2 * m 2 * (t 2 - t 1). The common factor (t 2 - t 1) can be taken out of the bracket to make it easier to calculate. Then the formula that will be required to calculate the amount of heat will take the following form: Q = (c 1 * m 1 + c 2 * m 2) * (t 2 - t 1). Now you can substitute the quantities known in the problem and calculate the result.
Q = (840 * 0.1 + 4200 * 0.05) * (100 - 0) = (84 + 210) * 100 = 294 * 100 = 29400 (J).
Answer. Q = 29400 J = 29.4 kJ.
/(kg K), etc.
Specific heat capacity is usually denoted by the letters c or WITH, often with indexes.
The specific heat capacity is affected by the temperature of the substance and other thermodynamic parameters. For example, measuring the specific heat capacity of water will give different results at 20 °C and 60 °C. In addition, specific heat capacity depends on how the thermodynamic parameters of the substance (pressure, volume, etc.) are allowed to change; for example, specific heat capacity at constant pressure ( C P) and at constant volume ( C V), generally speaking, are different.
Formula for calculating specific heat capacity:
Where c- specific heat capacity, Q- the amount of heat received by a substance when heated (or released when cooled), m- mass of the heated (cooled) substance, Δ T- the difference between the final and initial temperatures of the substance.
Specific heat capacity can depend (and in principle, strictly speaking, always, more or less strongly, depends) on temperature, therefore the following formula with small (formally infinitesimal) values is more correct: And :
Specific heat values for some substances
(For gases, the specific heat capacity in an isobaric process (C p) is given)
| Substance | Physical state | Specific heat capacity, kJ/(kg K) |
|---|---|---|
| air (dry) | gas | 1,005 |
| air (100% humidity) | gas | 1,0301 |
| aluminum | solid | 0,903 |
| beryllium | solid | 1,8245 |
| brass | solid | 0,37 |
| tin | solid | 0,218 |
| copper | solid | 0,385 |
| molybdenum | solid | 0,250 |
| steel | solid | 0,462 |
| diamond | solid | 0,502 |
| ethanol | liquid | 2,460 |
| gold | solid | 0,129 |
| graphite | solid | 0,720 |
| helium | gas | 5,190 |
| hydrogen | gas | 14,300 |
| iron | solid | 0,444 |
| lead | solid | 0,130 |
| cast iron | solid | 0,540 |
| tungsten | solid | 0,134 |
| lithium | solid | 3,582 |
| liquid | 0,139 | |
| nitrogen | gas | 1,042 |
| petroleum oils | liquid | 1,67 - 2,01 |
| oxygen | gas | 0,920 |
| quartz glass | solid | 0,703 |
| water 373 K (100 °C) | gas | 2,020 |
| water | liquid | 4,187 |
| ice | solid | 2,060 |
| beer wort | liquid | 3,927 |
| Values are based on standard conditions unless otherwise noted. | ||
| Substance | Specific heat capacity kJ/(kg K) |
|---|---|
| asphalt | 0,92 |
| solid brick | 0,84 |
| sand-lime brick | 1,00 |
| concrete | 0,88 |
| crown glass (glass) | 0,67 |
| flint (glass) | 0,503 |
| window glass | 0,84 |
| granite | 0,790 |
| soapstone | 0,98 |
| gypsum | 1,09 |
| marble, mica | 0,880 |
| sand | 0,835 |
| steel | 0,47 |
| soil | 0,80 |
| wood | 1,7 |
See also
Write a review about the article "Specific Heat Capacity"
Notes
Literature
- Tables of physical quantities. Handbook, ed. I. K. Kikoina, M., 1976.
- Sivukhin D.V. General course in physics. - T. II. Thermodynamics and molecular physics.
- E. M. Lifshits // under. ed. A. M. Prokhorova Physical Encyclopedia. - M.: “Soviet Encyclopedia”, 1998. - T. 2.<
Excerpt describing Specific Heat Capacity
- Does it work? – Natasha repeated.– I’ll tell you about myself. I had one cousin...
- I know - Kirilla Matveich, but he’s an old man?
– It wasn’t always an old man. But here’s what, Natasha, I’ll talk to Borya. He doesn't need to travel so often...
- Why shouldn’t he, if he wants to?
- Because I know that this will not end in anything.
- Why do you know? No, mom, you don't tell him. What nonsense! - Natasha said in the tone of a person from whom they want to take away his property.
“Well, I won’t get married, so let him go, if he’s having fun and I’m having fun.” – Natasha smiled and looked at her mother.
“Not married, just like that,” she repeated.
- How is this, my friend?
- Yes, yes. Well, it’s very necessary that I don’t get married, but... so.
“Yes, yes,” the countess repeated and, shaking her whole body, laughed with a kind, unexpected old woman’s laugh.
“Stop laughing, stop,” Natasha shouted, “you’re shaking the whole bed.” You look terribly like me, the same laugher... Wait... - She grabbed both hands of the countess, kissed the little finger bone on one - June, and continued to kiss July, August on the other hand. - Mom, is he very much in love? How about your eyes? Were you so in love? And very sweet, very, very sweet! But it’s not quite to my taste - it’s narrow, like a table clock... Don’t you understand?... Narrow, you know, gray, light...
- Why are you lying! - said the countess.
Natasha continued:
– Don’t you understand? Nikolenka would understand... The earless one is blue, dark blue with red, and he is quadrangular.
“You flirt with him too,” said the countess, laughing.
- No, he is a Freemason, I found out. It’s nice, dark blue and red, how can I explain it to you...
“Countess,” the count’s voice was heard from behind the door. -Are you awake? – Natasha jumped up barefoot, grabbed her shoes and ran into her room.
She couldn't sleep for a long time. She kept thinking that no one could understand everything that she understood and that was in her.
"Sonya?" she thought, looking at the sleeping, curled up cat with her huge braid. “No, where should she go!” She is virtuous. She fell in love with Nikolenka and doesn’t want to know anything else. Mom doesn’t understand either. It’s amazing how smart I am and how... she’s sweet,” she continued, speaking to herself in the third person and imagining that some very smart, smartest and nicest man was talking about her... “Everything, everything is in her.” , - continued this man, - she is unusually smart, sweet and then good, unusually good, dexterous, swims, rides excellently, and has a voice! One might say, an amazing voice!” She sang her favorite musical phrase from the Cherubini Opera, threw herself on the bed, laughed with the joyful thought that she was about to fall asleep, shouted to Dunyasha to put out the candle, and before Dunyasha had time to leave the room, she had already passed into another, even happier world of dreams , where everything was as easy and wonderful as in reality, but it was only even better, because it was different.
The next day, the countess, inviting Boris to her place, talked with him, and from that day he stopped visiting the Rostovs.
On December 31, on New Year's Eve 1810, le reveillon [night supper], there was a ball at Catherine's nobleman's house. The diplomatic corps and the sovereign were supposed to be at the ball.
On the Promenade des Anglais, the famous house of a nobleman glowed with countless lights. At the illuminated entrance with a red cloth stood the police, and not only gendarmes, but the police chief at the entrance and dozens of police officers. The carriages drove off, and new ones drove up with red footmen and footmen with feathered hats. Men in uniforms, stars and ribbons came out of the carriages; ladies in satin and ermine carefully stepped down the noisily laid down steps, and hurriedly and silently walked along the cloth of the entrance.
Almost every time a new carriage arrived, there was a murmur in the crowd and hats were taken off.
“Sovereign?... No, minister... prince... envoy... Don’t you see the feathers?...” said from the crowd. One of the crowd, better dressed than the others, seemed to know everyone, and called by name the most noble nobles of that time.
Already one third of the guests had arrived at this ball, and the Rostovs, who were supposed to be at this ball, were still hastily preparing to dress.
There was a lot of talk and preparation for this ball in the Rostov family, a lot of fears that the invitation would not be received, the dress would not be ready, and everything would not work out as needed.
Along with the Rostovs, Marya Ignatievna Peronskaya, a friend and relative of the countess, a thin and yellow maid of honor of the old court, leading the provincial Rostovs in the highest St. Petersburg society, went to the ball.
At 10 o'clock in the evening the Rostovs were supposed to pick up the maid of honor at the Tauride Garden; and yet it was already five minutes to ten, and the young ladies were not yet dressed.
Natasha was going to the first big ball in her life. That day she got up at 8 o'clock in the morning and was in feverish anxiety and activity all day. All her strength, from the very morning, was aimed at ensuring that all of them: she, mother, Sonya were dressed in the best possible way. Sonya and the Countess trusted her completely. The countess was supposed to be wearing a masaka velvet dress, the two of them were wearing white smoky dresses on pink, silk covers with roses in the bodice. The hair had to be combed a la grecque [in Greek].
Everything essential had already been done: the legs, arms, neck, ears were already especially carefully, like a ballroom, washed, perfumed and powdered; they were already wearing silk, fishnet stockings and white satin shoes with bows; the hairstyles were almost finished. Sonya finished dressing, and so did the Countess; but Natasha, who was working for everyone, fell behind. She was still sitting in front of the mirror with a peignoir draped over her thin shoulders. Sonya, already dressed, stood in the middle of the room and, pressing painfully with her small finger, pinned the last ribbon that squealed under the pin.
The change in internal energy by doing work is characterized by the amount of work, i.e. work is a measure of the change in internal energy in a given process. The change in the internal energy of a body during heat transfer is characterized by a quantity called the amount of heat.
is a change in the internal energy of a body during the process of heat transfer without performing work. The amount of heat is indicated by the letter Q .
Work, internal energy and heat are measured in the same units - joules ( J), like any type of energy.
In thermal measurements, a special unit of energy was previously used as a unit of heat quantity - the calorie ( feces), equal to the amount of heat required to heat 1 gram of water by 1 degree Celsius (more precisely, from 19.5 to 20.5 ° C). This unit, in particular, is currently used when calculating heat consumption (thermal energy) in apartment buildings. The mechanical equivalent of heat has been experimentally established - the relationship between calorie and joule: 1 cal = 4.2 J.
When a body transfers a certain amount of heat without doing work, its internal energy increases; if the body gives off a certain amount of heat, then its internal energy decreases.
If you pour 100 g of water into two identical vessels, one and 400 g into the other at the same temperature and place them on identical burners, then the water in the first vessel will boil earlier. Thus, the greater the body mass, the greater the amount of heat it requires to warm up. It's the same with cooling.
The amount of heat required to heat a body also depends on the type of substance from which the body is made. This dependence of the amount of heat required to heat a body on the type of substance is characterized by a physical quantity called specific heat capacity substances.
is a physical quantity equal to the amount of heat that must be imparted to 1 kg of a substance to heat it by 1 °C (or 1 K). 1 kg of substance releases the same amount of heat when cooled by 1 °C.
Specific heat capacity is designated by the letter With. The unit of specific heat capacity is 1 J/kg °C or 1 J/kg °K.
The specific heat capacity of substances is determined experimentally. Liquids have a higher specific heat capacity than metals; Water has the highest specific heat, gold has a very small specific heat.
Since the amount of heat is equal to the change in the internal energy of the body, we can say that the specific heat capacity shows how much the internal energy changes 1 kg substance when its temperature changes by 1 °C. In particular, the internal energy of 1 kg of lead increases by 140 J when heated by 1 °C, and decreases by 140 J when cooled.
Q required to heat a body of mass m on temperature t 1 °С up to temperature t 2 °С, is equal to the product of the specific heat capacity of the substance, body mass and the difference between the final and initial temperatures, i.e.Q = c ∙ m (t 2 - t 1)
The same formula is used to calculate the amount of heat that a body gives off when cooling. Only in this case should the final temperature be subtracted from the initial temperature, i.e. Subtract the smaller temperature from the larger temperature.
This is a summary of the topic “Amount of heat. Specific heat". Select next steps:
- Go to next summary:
