The specific heat capacity of a substance is a unit of measurement. Specific heat capacity: what is it for and what is its meaning

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

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

Internet portal "vactekh-holod.ru" ()

Homework

Every schoolchild comes across in physics lessons with such a concept as "specific heat capacity". In most cases, people forget the school definition, and often do not understand the meaning of this term at all. In technical universities, most students will sooner or later encounter specific heat. Perhaps, as part of the study of physics, or maybe someone will have such a discipline as "heat engineering" or "technical thermodynamics". In this case, you will have to remember the school curriculum. So, below is the definition, examples, meanings for some substances.

Definition

Specific heat capacity is a physical quantity that characterizes how much heat must be supplied to a unit of a substance or removed from a unit of a substance in order for its temperature to change by one degree. It is important to cancel that it does not matter, degrees Celsius, Kelvin and Fahrenheit, the main thing is the change in temperature per unit.

Specific heat capacity has its own unit of measurement - in the international system of units (SI) - Joule divided by the product of a kilogram and a degree Kelvin, J / (kg K); the off-system unit is the ratio of a calorie to the product of a kilogram and a degree Celsius, cal/(kg °C). This value is most often denoted by the letter c or C, sometimes indices are used. For example, if the pressure is constant, then the index is p, and if the volume is constant, then v.

Definition Variations

Several formulations of the definition of the discussed physical quantity are possible. In addition to the above, a definition is considered acceptable, which states that the specific heat capacity is the ratio of the value of the heat capacity of a substance to its mass. In this case, it is necessary to clearly understand what "heat capacity" is. So, heat capacity is called a physical quantity that shows how much heat must be brought to the body (substance) or removed in order to change the value of its temperature by one. The specific heat capacity of a mass of a substance greater than a kilogram is determined in the same way as for a single value.

Some examples and meanings for various substances

It has been experimentally found that this value is different for different substances. For example, the specific heat capacity of water is 4.187 kJ/(kg K). The largest value of this physical quantity for hydrogen is 14.300 kJ/(kg·K), the smallest value for gold is 0.129 kJ/(kg·K). If you need a value for a particular substance, then you need to take a reference book and find the corresponding tables, and in them - the values \u200b\u200bof you are interested. However, modern technologies make it possible to speed up the search process at times - it is enough on any phone that has the option to enter the World Wide Web, type the question of interest in the search bar, start the search and look for the answer based on the results. In most cases, you need to click on the first link. However, sometimes you don’t need to go anywhere else at all - the answer to the question is visible in a brief description of the information.

The most common substances for which they are looking for heat capacity, including specific heat, are:

air (dry) - 1.005 kJ / (kg K),
aluminum - 0.930 kJ / (kg K),
copper - 0.385 kJ / (kg K),
ethanol - 2.460 kJ / (kg K),
iron - 0.444 kJ / (kg K),
mercury - 0.139 kJ / (kg K),
oxygen - 0.920 kJ / (kg K),
wood - 1,700 kJ/(kg K),
sand - 0.835 kJ/(kg K).

The amount of energy that must be supplied to 1 g of a substance in order to raise its temperature by 1 ° C. By definition, in order to raise the temperature of 1 g of water by 1 ° C, it takes 4.18 J. Ecological Encyclopedic Dictionary. ... ... Ecological dictionary

specific heat- - [A.S. Goldberg. English Russian Energy Dictionary. 2006] Topics energy in general EN specific heatSH …

SPECIFIC HEAT- physical. a quantity measured by the amount of heat required to heat 1 kg of a substance by 1 K (see). The unit of specific heat capacity in SI (see) per kilogram kelvin (J kg ∙ K)) ... Great Polytechnic Encyclopedia

specific heat- savitoji šiluminė talpa statusas T sritis fizika atitikmenys: engl. heat capacity per unit mass; mass heat capacity; specific heat capacity vok. Eigenwarme, f; spezifice Wärme, f; spezifische Wärmekapazität, f rus. mass heat capacity, f;… … Fizikos terminų žodynas

See heat capacity... Great Soviet Encyclopedia

specific heat- specific heat... Dictionary of chemical synonyms I

specific heat capacity of gas- — Topics oil and gas industry EN gas specific heat … Technical Translator's Handbook

specific heat capacity of oil- — Topics oil and gas industry EN oil specific heat … Technical Translator's Handbook

specific heat capacity at constant pressure- - [A.S. Goldberg. English Russian Energy Dictionary. 2006] Topics energy in general EN specific heat at constant pressurecpconstant pressure specific heat … Technical Translator's Handbook

specific heat capacity at constant volume- - [A.S. Goldberg. English Russian Energy Dictionary. 2006] Topics energy in general EN specific heat at constant volumeconstant volume specific heatCv … Technical Translator's Handbook

Books

Physical and geological foundations for studying the movement of water in deep horizons, Trushkin V.V. In general, the book is devoted to the law of autoregulation of water temperature with a host body, discovered by the author in 1991. At the beginning of the book, a review of the state of knowledge of the problem of movement of deep ...

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.