Instruments and accessories used in the work:

2. Weights.

3. Thermometer.

4. Calorimeter.

6. Calorimetric body.

7. Household tiles.

Objective:

To learn experimentally to determine the specific heat capacity of a substance.

I. THEORETICAL INTRODUCTION.

Thermal conductivity- transfer of heat from more heated parts of the body to less heated ones as a result of collisions of fast molecules with slow ones, as a result of which fast molecules transfer part of their energy to slow ones.

The change in the internal energy of any body is directly proportional to its mass and change in body temperature.

DU=cmDT(1)
Q=cmDT(2)

The value c characterizing the dependence of the change in the internal energy of the body during heating or cooling on the type of substance and external conditions is called specific heat capacity of the body.

(4)

The value C, which characterizes the dependence of the body to absorb heat when heated and is equal to the ratio of the amount of heat communicated to the body to the increment in its temperature, is called heat capacity of the body.

C = c × m. (5)
(6)
Q=CDT(7)

Molar heat capacity C m , is the amount of heat required to raise the temperature of one mole of a substance by 1 Kelvin

Cm = cM. (eight)
C m = (9)

The specific heat capacity depends on the nature of the process in which it is heated.

Heat balance equation.

During heat transfer, the sum of the amounts of heat given away by all bodies, in which the internal energy decreases, is equal to the sum of the amounts of heat received by all bodies, in which the internal energy increases.

SQ out = SQ in (10)

If the bodies form a closed system and only heat exchange occurs between them, then the algebraic sum of the received and given amounts of heat is 0.

SQ out + SQ in = 0.

Example:

A body, a calorimeter, and a liquid participate in heat transfer. The body gives off heat, the calorimeter and liquid receive.

Q t \u003d Q k + Q f

Q t \u003d c t m t (T 2 - Q)

Q to = c to m to (Q - T 1)

Q f = c f m f (Q - T 1)

Where Q(tau) is the total final temperature.

with t m t (T 2 -Q) \u003d with to m to (Q- T 1) + with f m f (Q- T 1)

with t \u003d ((Q - T 1) * (s to m k + c f m g)) / m t (T 2 - Q)

T \u003d 273 0 + t 0 C

2. PROGRESS OF WORK.

ALL WEIGHINGS SHOULD BE CARRIED OUT WITH 0.1 g ACCURACY.

1. Determine by weighing the mass of the inner vessel, calorimeter m 1 .

2. Pour water into the inner vessel of the calorimeter, weigh the inner beaker together with the poured liquid m k.

3. Determine the mass of poured water m \u003d m to - m 1

4. Place the inner vessel of the calorimeter in the outer vessel and measure the initial water temperature T 1 .

5. Remove the test body from boiling water, quickly transfer it to the calorimeter, determining T 2 - the initial temperature of the body, it is equal to the temperature of boiling water.

6. While stirring the liquid in the calorimeter, wait until the temperature stops rising: measure the final (steady) temperature Q.

7. Remove the test body from the calorimeter, dry it with filter paper and weigh it on a balance to determine its mass m 3 .

8. Record the results of all measurements and calculations in the table. Perform calculations up to the second decimal place.

9. Make a heat balance equation and find from it the specific heat capacity of a substance with.

10. Based on the results obtained, determine the substance in the application.

11. Calculate the absolute and relative error of the result obtained relative to the tabular result using the formulas:

;

12. Conclusion about the work done.

TABLE OF MEASUREMENT AND CALCULATION RESULTS

Water is one of the most amazing substances. Despite its wide distribution and widespread use, it is a real mystery of nature. Being one of the oxygen compounds, it would seem that water should have very low characteristics such as freezing, heat of vaporization, etc. But this does not happen. The heat capacity of water alone, in spite of everything, is extremely high.

Water is able to absorb a huge amount of heat, while itself practically not heating up - this is its physical feature. water is about five times higher than the heat capacity of sand, and ten times higher than iron. Therefore, water is a natural coolant. Its ability to accumulate a large amount of energy makes it possible to smooth out temperature fluctuations on the Earth's surface and regulate the thermal regime throughout the planet, and this happens regardless of the time of year.

This unique property of water makes it possible to use it as a coolant in industry and at home. In addition, water is a widely available and relatively cheap raw material.

What is meant by heat capacity? As is known from the course of thermodynamics, heat transfer always occurs from a hot to a cold body. In this case, we are talking about the transition of a certain amount of heat, and the temperature of both bodies, being a characteristic of their state, shows the direction of this exchange. In the process of a metal body with water of equal mass at the same initial temperatures, the metal changes its temperature several times more than water.

If we take as a postulate the main statement of thermodynamics - from two bodies (isolated from others), during heat exchange, one gives off and the other receives an equal amount of heat, then it becomes clear that metal and water have completely different heat capacities.

Thus, the heat capacity of water (as well as any substance) is an indicator that characterizes the ability of a given substance to give (or receive) some during cooling (heating) per unit temperature.

The specific heat capacity of a substance is the amount of heat required to heat a unit of this substance (1 kilogram) by 1 degree.

The amount of heat released or absorbed by a body is equal to the product of specific heat capacity, mass and temperature difference. It is measured in calories. One calorie is exactly the amount of heat that is enough to heat 1 g of water by 1 degree. For comparison: the specific heat capacity of air is 0.24 cal/g ∙°C, aluminum is 0.22, iron is 0.11, and mercury is 0.03.

The heat capacity of water is not a constant. With an increase in temperature from 0 to 40 degrees, it slightly decreases (from 1.0074 to 0.9980), while for all other substances this characteristic increases during heating. In addition, it can decrease with increasing pressure (at depth).

As you know, water has three states of aggregation - liquid, solid (ice) and gaseous (steam). At the same time, the specific heat capacity of ice is approximately 2 times lower than that of water. This is the main difference between water and other substances, the specific heat capacity of which in the solid and molten state does not change. What is the secret here?

The fact is that ice has a crystalline structure, which does not immediately collapse when heated. Water contains small particles of ice, which consist of several molecules and are called associates. When water is heated, a part is spent on the destruction of hydrogen bonds in these formations. This explains the unusually high heat capacity of water. The bonds between its molecules are completely destroyed only when water passes into steam.

The specific heat capacity at a temperature of 100°C almost does not differ from that of ice at 0°C. This once again confirms the correctness of this explanation. The heat capacity of steam, like the heat capacity of ice, is now much better understood than that of water, on which scientists have not yet come to a consensus.

What do you think heats up faster on the stove: a liter of water in a saucepan or the saucepan itself weighing 1 kilogram? The mass of the bodies is the same, it can be assumed that heating will occur at the same rate.

But it wasn't there! You can do an experiment - put an empty saucepan on the fire for a few seconds, just do not burn it, and remember to what temperature it has heated up. And then pour water into the pan of exactly the same weight as the weight of the pan. In theory, the water should heat up to the same temperature as an empty pan in twice the time, since in this case both of them are heated - both the water and the pan.

However, even if you wait three times as long, make sure that the water is still less heated. It takes almost ten times longer for water to heat up to the same temperature as a pot of the same weight. Why is this happening? What stops water from heating up? Why should we waste extra gas to heat water when cooking? Because there is a physical quantity called the specific heat capacity of a substance.

Specific heat capacity of a substance

This value shows how much heat must be transferred to a body with a mass of one kilogram in order for its temperature to increase by one degree Celsius. It is measured in J / (kg * ˚С). This value exists not on a whim, but because of the difference in the properties of various substances.

The specific heat of water is about ten times the specific heat of iron, so the pot will heat up ten times faster than the water in it. Curiously, the specific heat capacity of ice is half that of water. Therefore, ice will heat up twice as fast as water. Melting ice is easier than heating water. As strange as it sounds, it is a fact.

Calculation of the amount of heat

The specific heat capacity is denoted by the letter c and used in the formula for calculating the amount of heat:

Q = c*m*(t2 - t1),

where Q is the amount of heat,
c - specific heat capacity,
m - body weight,
t2 and t1 are, respectively, the final and initial temperatures of the body.

Specific heat formula: c = Q / m*(t2 - t1)

You can also express from this formula:

• m = Q / c*(t2-t1) - body weight
• t1 = t2 - (Q / c*m) - initial body temperature
• t2 = t1 + (Q / c*m) - final body temperature
• Δt = t2 - t1 = (Q / c*m) - temperature difference (delta t)

What about the specific heat capacity of gases? Everything is more confusing here. With solids and liquids, the situation is much simpler. Their specific heat capacity is a constant, known, easily calculated value. As for the specific heat capacity of gases, this value is very different in different situations. Let's take air as an example. The specific heat capacity of air depends on the composition, humidity, and atmospheric pressure.

At the same time, with an increase in temperature, the gas increases in volume, and we need to introduce one more value - a constant or variable volume, which will also affect the heat capacity. Therefore, when calculating the amount of heat for air and other gases, special graphs of the values ​​of the specific heat capacity of gases are used depending on various factors and conditions.

In today's lesson, we will introduce such a physical concept as the specific heat capacity of a substance. We learn that it depends on the chemical properties of the substance, and its value, which can be found in the tables, is different for different substances. Then we will find out the units of measurement and the formula for finding the specific heat capacity, and also learn how to analyze the thermal properties of substances by the value of their specific heat capacity.

Calorimeter(from lat. calories- warm and metor- measure) - a device for measuring the amount of heat released or absorbed in any physical, chemical or biological process. The term "calorimeter" was proposed by A. Lavoisier and P. Laplace.

The calorimeter consists of a cover, internal and external glass. It is very important in the design of the calorimeter that there is a layer of air between the smaller and larger vessels, which, due to low thermal conductivity, provides poor heat transfer between the contents and the external environment. This design makes it possible to consider the calorimeter as a kind of thermos and practically get rid of the influence of the external environment on the course of heat transfer processes inside the calorimeter.

The calorimeter is intended for more accurate measurements of specific heat capacities and other thermal parameters of bodies than indicated in the table.

Comment. It is important to note that such a concept as the amount of heat, which we use very often, should not be confused with the internal energy of the body. The amount of heat determines precisely the change in internal energy, and not its specific value.

Note that the specific heat capacity of different substances is different, which can be seen from the table (Fig. 3). For example, gold has a specific heat capacity. As we have already pointed out earlier, the physical meaning of this specific heat capacity means that in order to heat 1 kg of gold by 1 °C, it needs to be supplied with 130 J of heat (Fig. 5).

Rice. 5. Specific heat capacity of gold

In the next lesson, we will discuss how to calculate the amount of heat.

Listliterature

1. Gendenstein L.E., Kaidalov A.B., Kozhevnikov V.B. / Ed. Orlova V.A., Roizena I.I. Physics 8. - M.: Mnemosyne.
2. Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
3. Fadeeva A.A., Zasov A.V., Kiselev D.F. Physics 8. - M.: Enlightenment.

1. Internet portal "vactekh-holod.ru" ()

Homework

/(kg K), etc.

Specific heat capacity is usually denoted by the letters c or With, often with indices.

The value of specific heat 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, the specific heat capacity depends on how the thermodynamic parameters of the substance (pressure, volume, etc.) are allowed to change; for example, the specific heat capacity at constant pressure ( C P) and at constant volume ( C V) are generally different.

The formula for calculating the specific heat capacity:

$c=\backslash frac(Q)(\; m\backslash Delta\; T),$ where c- specific heat capacity, Q- the amount of heat received by the substance during heating (or released during cooling), m- mass of the heated (cooled) substance, Δ T- the difference between the final and initial temperatures of the substance.

The specific heat capacity can depend (and in principle, strictly speaking, always, more or less strongly, depends) on temperature, so the following formula with small (formally infinitesimal) is more correct: $\backslash delta\; T$ and $\backslash delta\; Q$:

$c(T)\; =\; \backslash frac\; 1\; (m)\; \backslash left(\backslash frac(\backslash delta\; Q)(\backslash delta\; T)\backslash right).$

The values ​​of the specific heat capacity of some substances

(For gases, the values ​​of the specific heat in the isobaric process (C p))

Table I: Typical specific heat values

Substance	State of aggregation	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 for standard conditions unless otherwise noted.

Table II: Specific heat values ​​for some building materials

Substance	Specific heat capacity kJ/(kg K)
asphalt	0,92
solid brick	0,84
silicate brick	1,00
concrete	0,88
kronglas (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
the soil	0,80
wood	1,7

see also

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Notes

Literature

• Tables of physical quantities. Handbook, ed. I. K. Kikoina, M., 1976.
• Sivukhin DV General course of physics. - T. II. Thermodynamics and molecular physics.
• E. M. Lifshitz // under. ed. A. M. Prokhorova Physical Encyclopedia. - M .: "Soviet Encyclopedia", 1998. - T. 2.<

An excerpt characterizing Specific heat capacity

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- I know - Kirilla Matveich, but he is an old man?
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- How is it, my friend?
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“So, so,” repeated the countess, and, shaking with her whole body, she laughed a kind, unexpected old woman’s laugh.
- Stop laughing, stop it, - Natasha shouted, - you are shaking the whole bed. You look terribly like me, the same laughter ... Wait a minute ... - She grabbed both hands of the countess, kissed the bone of the little finger on one - June, and continued to kiss July, August on the other hand. - Mom, is he very in love? How about your eyes? Were you so in love? And very nice, very, very nice! Only not quite to my taste - it is narrow, like a dining room clock ... Don't you understand? ... Narrow, you know, gray, light ...
– What are you lying about! said the Countess.
Natasha continued:
- Do you really not understand? Nikolenka would understand... Earless - that blue, dark blue with red, and it is quadrangular.
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She couldn't sleep for a long time. She kept thinking about the fact that no one can understand everything that she understands and what is in her.
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The next day, the countess, having invited Boris to her place, had a talk with him, and from that day he stopped visiting the Rostovs.

On the 31st of December, on the eve of the new year 1810, le reveillon [night dinner], there was a ball at the Catherine's nobleman. The ball was supposed to be the diplomatic corps and the sovereign.
On the Promenade des Anglais, the famous house of a nobleman shone with countless lights of illumination. At the illuminated entrance with red cloth stood the police, and not only the gendarmes, but the police chief at the entrance and dozens of police officers. The carriages drove off, and new ones kept coming up with red footmen and with footmen in feathers on their hats. Men in uniforms, stars and ribbons came out of the carriages; ladies in satin and ermine carefully descended the noisily laid steps, and hurriedly and soundlessly passed along the cloth of the entrance.
Almost every time a new carriage drove up, a whisper ran through the crowd and hats were taken off.
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One-third of the guests had already arrived at this ball, and the Rostovs, who were supposed to be at this ball, were still hastily preparing to dress.
There were many rumors and preparations for this ball in the Rostov family, many fears that the invitation would not be received, the dress would not be ready, and everything would not work out as it should.
Together with the Rostovs, Marya Ignatievna Peronskaya, a friend and relative of the countess, a thin and yellow maid of honor of the old court, who led the provincial Rostovs in the highest St. Petersburg society, went to the ball.
At 10 pm, the Rostovs were supposed to call for the maid of honor to the Tauride Garden; and meanwhile it was already five minutes to ten, and the young ladies were still not dressed.
Natasha was going to the first big ball in her life. She got up that day at 8 o'clock in the morning and was in feverish anxiety and activity all day long. All her strength, from the very morning, was focused on ensuring that they all: she, mother, Sonya were dressed in the best possible way. Sonya and the countess vouched for her completely. The countess was supposed to be wearing a masaka velvet dress, they were wearing two white smoky dresses on pink, silk cases with roses in the corsage. The hair had to be combed a la grecque [Greek].
Everything essential had already been done: the legs, arms, neck, ears were already especially carefully, according to the ballroom, washed, perfumed and powdered; shod already were silk, fishnet stockings and white satin shoes with bows; the hair was almost finished. Sonya finished dressing, the countess too; but Natasha, who worked for everyone, fell behind. She was still sitting in front of the mirror in a peignoir draped over her thin shoulders. Sonya, already dressed, stood in the middle of the room and, pressing painfully with her little finger, pinned the last ribbon that squealed under the pin.