Formula for the amount of heat required for heating. Calculation of the amount of heat during heat transfer, specific heat capacity of a substance

12.10.2019

In this lesson, we will learn how to calculate the amount of heat required to heat a body or released by it when it cools. To do this, we will summarize the knowledge that was gained in the previous lessons.

In addition, we will learn to use the formula for the amount of heat to express the remaining quantities from this formula and calculate them, knowing other quantities. An example of a problem with a solution to calculate the amount of heat will also be considered.

This lesson is devoted to calculating the amount of heat when a body is heated or released by it when it is cooled.

The ability to calculate the required amount of heat is very important. This may be necessary, for example, when calculating the amount of heat that must be supplied to water to heat a room.

Rice. 1. The amount of heat that must be supplied to the water to heat the room

Or to calculate the amount of heat that is released when fuel is burned in various engines:

Rice. 2. The amount of heat that is released when burning fuel in the engine

Also, this knowledge is needed, for example, to determine the amount of heat that is released by the Sun and falls on the Earth:

Rice. 3. The amount of heat released by the Sun and falling on the Earth

To calculate the amount of heat, you need to know three things (Fig. 4):

body weight (which can usually be measured with a scale);
the temperature difference by which it is necessary to heat the body or cool it (usually measured with a thermometer);
specific heat capacity of the body (which can be determined from the table).

Rice. 4. What you need to know to determine

The formula by which the amount of heat is calculated looks like this:

The following quantities appear in this formula:

The amount of heat, measured in joules (J);

Specific heat of a substance, measured in;

- temperature difference, measured in degrees Celsius ().

Consider the problem of calculating the amount of heat.

Task

A copper glass weighing a gram contains water with a volume of a liter at a temperature. How much heat must be transferred to a glass of water so that its temperature becomes equal?

Rice. 5. Illustration of the problem statement

First, we write down a short condition ( Given) and translate all values into the international system (SI).

*Given:*	SI

*Find:*

Solution:

First, determine what other quantities we need to solve this problem. According to the table of specific heat capacity (Table 1) we find (specific heat capacity of copper, since according to the condition the glass is copper), (specific heat capacity of water, since according to the condition there is water in the glass). In addition, we know that we need a mass of water to calculate the amount of heat. By condition, only the volume is given to us. Therefore, we take the density of water from the table: (Table 2).

Tab. 1. Specific heat of some substances,

Tab. 2. Densities of some liquids

Now we have everything we need to solve this problem.

Note that the total amount of heat will consist of the sum of the amount of heat required to heat the copper glass and the amount of heat required to heat the water in it:

Let us first calculate the amount of heat required to heat the copper glass:

Before calculating the amount of heat required to heat water, let's calculate the mass of water using a formula that is well known to us from grade 7:

Now we can calculate:

Then we can calculate:

Let's remind what means: kilojoules. The prefix "kilo" means, that is .

Answer:.

For the convenience of solving problems of finding the amount of heat (the so-called direct problems) and the quantities associated with this concept, you can use the following table.

The sought value	Designation	Units	Basic formula	Formula for quantity
Quantity of heat

The process of transferring energy from one body to another without doing work is called heat exchange or heat transfer... Heat transfer occurs between bodies with different temperatures. When contact is established between bodies with different temperatures, part of the internal energy is transferred from a body with a higher temperature to a body with a lower temperature. The energy transferred to the body as a result of heat exchange is called the amount of warmth.

Specific heat of a substance:

If the heat transfer process is not accompanied by work, then on the basis of the first law of thermodynamics, the amount of heat is equal to the change in the internal energy of the body:.

The average energy of the random translational motion of molecules is proportional to the absolute temperature. The change in the internal energy of a body is equal to the algebraic sum of changes in the energy of all atoms or molecules, the number of which is proportional to the mass of the body, therefore, the change in internal energy and, therefore, the amount of heat is proportional to the mass and temperature change:

The proportionality factor in this equation is called specific heat of a substance... Specific heat shows how much heat is needed to heat 1 kg of a substance per 1 K.

Work in thermodynamics:

In mechanics, work is defined as the product of the modules of force and displacement and the cosine of the angle between them. The work is performed when a force acts on a moving body and is equal to a change in its kinetic energy.

In thermodynamics, the movement of a body as a whole is not considered, it is about the movement of parts of a macroscopic body relative to each other. As a result, the volume of the body changes, and its speed remains equal to zero. Work in thermodynamics is defined in the same way as in mechanics, but it is equal to a change not in the kinetic energy of a body, but in its internal energy.

When work is done (compression or expansion), the internal energy of the gas changes. The reason for this is as follows: during elastic collisions of gas molecules with a moving piston, their kinetic energy changes.

Let's calculate the work of the gas during expansion. The gas acts on the piston with force
, where - gas pressure, and - surface area piston. When the gas expands, the piston moves in the direction of the force short distance
... If the distance is small, then the gas pressure can be considered constant. Gas work is equal to:

Where
- change in gas volume.

In the process of expansion, the gas does positive work, since the direction of the force and the movement coincide. In the process of expansion, the gas gives up energy to the surrounding bodies.

The work done by external bodies on the gas differs from the work of the gas only by the sign
since the strength acting on the gas is opposite to the force , with which the gas acts on the piston, and is equal to it in absolute value (Newton's third law); and the movement remains the same. Therefore, the work of external forces is equal to:

The first law of thermodynamics:

The first law of thermodynamics is the law of conservation of energy, extended to thermal phenomena. Law of energy conservation: energy in nature does not arise from nothing and does not disappear: the amount of energy is invariable, it only passes from one form to another.

In thermodynamics, bodies are considered, the position of the center of gravity of which practically does not change. The mechanical energy of such bodies remains constant, and only the internal energy can change.

Internal energy can be changed in two ways: by heat transfer and by doing work. In the general case, the internal energy changes both due to heat transfer and due to the performance of work. The first law of thermodynamics is formulated precisely for such general cases:

The change in the internal energy of the system during its transition from one state to another is equal to the sum of the work of external forces and the amount of heat transferred to the system:

If the system is isolated, then no work is done on it and it does not exchange heat with the surrounding bodies. According to the first law of thermodynamics the internal energy of an isolated system remains unchanged.

Considering that
, the first law of thermodynamics can be written as follows:

The amount of heat transferred to the system is used to change its internal energy and to work on external bodies by the system..

The second law of thermodynamics: it is impossible to transfer heat from a colder system to a hotter one in the absence of other simultaneous changes in both systems or in the surrounding bodies.

721. Why is water used to cool some mechanisms?
Water has a high specific heat, which contributes to good heat dissipation from the mechanism.

722. In which case it is necessary to spend more energy: for heating one liter of water by 1 ° C or for heating one hundred grams of water by 1 ° C?
To heat a liter of water, since the greater the mass, the more energy you need to spend.

723. Cupronickel and silver forks of the same mass were dipped into hot water. Will they receive the same amount of heat in water?
Cupronickel plug will receive more heat, because the specific heat of cupronickel is greater than that of silver.

724. A piece of lead and a piece of cast iron of the same mass were struck three times with a sledgehammer. Which piece is hotter?
Lead will heat up more because it has a lower specific heat than cast iron and requires less energy to heat the lead.

725. In one flask there is water, in the other there is kerosene of the same mass and temperature. An equally heated iron cube was thrown into each flask. Which will heat up to a higher temperature - water or kerosene?
Kerosene.

726. Why in cities on the seashore temperature fluctuations in winter and summer are less sharp than in cities located in the interior of the continent?
Water heats up and cools more slowly than air. In winter, it cools down and moves warm air masses to land, making the climate on the coast warmer.

727. The specific heat capacity of aluminum is 920 J / kg ° C. What does this mean?
This means that to heat 1 kg of aluminum at 1 ° C, 920 J.

728. Aluminum and copper bars of the same weight 1 kg are cooled by 1 ° C. How much will the internal energy of each bar change? Which bar will it change more and by how much?

729. What amount of heat is needed to heat a kilogram iron billet by 45 ° C?

730. What amount of heat is required to heat 0.25 kg of water from 30 ° C to 50 ° C?

731. How will the internal energy of two liters of water change when heated by 5 ° C?

732. What amount of heat is needed to heat 5 g of water from 20 ° C to 30 ° C?

733. What amount of heat is needed to heat an aluminum ball weighing 0.03 kg at 72 ° C?

734. Calculate the amount of heat required to heat 15 kg of copper at 80 ° C.

735. Calculate the amount of heat required to heat 5 kg of copper from 10 ° C to 200 ° C.

736. What amount of heat is required to heat 0.2 kg of water from 15 ° C to 20 ° C?

737. Water weighing 0.3 kg cooled down by 20 ° C. How much has the internal energy of water decreased?

738. What amount of heat is needed to heat 0.4 kg of water at a temperature of 20 ° C to a temperature of 30 ° C?

739. What amount of heat is spent on heating 2.5 kg of water at 20 ° C?

740. What amount of heat was released during cooling of 250 g of water from 90 ° C to 40 ° C?

741. What amount of heat is required to heat 0.015 l of water by 1 ° C?

742. Calculate the amount of heat required to heat a 300 m3 pond by 10 ° C?

743. What amount of heat must be imparted to 1 kg of water in order to raise its temperature from 30 ° С to 40 ° С?

744. Water with a volume of 10 liters has cooled from a temperature of 100 ° C to a temperature of 40 ° C. How much heat was released during this?

745. Calculate the amount of heat required to heat 1 m3 of sand to 60 ° C.

746. Air volume 60 m3, specific heat capacity 1000 J / kg ° С, air density 1.29 kg / m3. How much heat is needed to heat it up to 22 ° C?

747. The water was heated by 10 ° C, using 4.20 103 J of heat. Determine the amount of water.

748. Water weighing 0.5 kg was reported 20.95 kJ of heat. What was the water temperature if the initial water temperature was 20 ° C?

749. A copper saucepan weighing 2.5 kg is filled with 8 kg of water at 10 ° C. How much heat is needed to bring the water in a saucepan to a boil?

750. A liter of water at a temperature of 15 ° C is poured into a copper ladle weighing 300 g. What amount of heat is needed to heat the water in the ladle to 85 ° C?

751. A piece of heated granite weighing 3 kg is placed in water. Granite transfers 12.6 kJ of heat to water, cooling by 10 ° C. What is the specific heat of the stone?

752. Hot water at 50 ° C was added to 5 kg of water at 12 ° C to obtain a mixture with a temperature of 30 ° C. How much water was added?

753. Water at 20 ° C was added to 3 liters of water at 60 ° C to obtain water at 40 ° C. How much water was added?

754. What will be the temperature of the mixture if you mix 600 g of water at 80 ° C with 200 g of water at 20 ° C?

755. A liter of water at 90 ° C was poured into water at 10 ° C, and the temperature of the water became 60 ° C. How much cold water was there?

756. Determine how much hot water heated to 60 ° C should be poured into the vessel if the vessel already contains 20 liters of cold water at a temperature of 15 ° C; the temperature of the mixture should be 40 ° C.

757. Determine how much heat is required to heat 425 g of water at 20 ° C.

758. How many degrees will 5 kg of water heat up if the water receives 167.2 kJ?

759. How much heat is required to heat m grams of water at temperature t1 to temperature t2?

760. The calorimeter is filled with 2 kg of water at a temperature of 15 ° C. To what temperature will the calorimeter's water be heated if a brass weight of 500 g, heated to 100 ° C, is lowered into it? The specific heat capacity of brass is 0.37 kJ / (kg ° C).

761. There are lumps of copper, tin and aluminum of the same volume. Which of these pieces has the highest and lowest heat capacity?

762. The calorimeter was filled with 450 g of water, the temperature of which was 20 ° C. When 200 g of iron filings heated to 100 ° C were immersed in this water, the water temperature became 24 ° C. Determine the specific heat of the sawdust.

763. A copper calorimeter weighing 100 g holds 738 g of water, the temperature of which is 15 ° C. 200 g of copper was lowered into this calorimeter at a temperature of 100 ° C, after which the temperature of the calorimeter rose to 17 ° C. What is the specific heat of copper?

764. A steel ball weighing 10 g is taken out of the oven and immersed in water at a temperature of 10 ° C. The water temperature rose to 25 ° C. What was the temperature of the ball in the oven if the mass of water was 50 g? The specific heat capacity of steel is 0.5 kJ / (kg ° C).

770. A steel cutter weighing 2 kg was heated to a temperature of 800 ° C and then lowered into a vessel containing 15 liters of water at a temperature of 10 ° C. To what temperature will the water in the vessel be heated?

(Note. To solve this problem, it is necessary to draw up an equation in which the unknown temperature of the water in the vessel after lowering the cutter is taken as the unknown.)

771. What is the temperature of water if you mix 0.02 kg of water at 15 ° C, 0.03 kg of water at 25 ° C and 0.01 kg of water at 60 ° C?

772. Heating of a well-ventilated class requires an amount of heat 4.19 MJ per hour. Water enters the heating radiators at 80 ° C, and leaves them at 72 ° C. How much water do you need to supply every hour to the radiators?

773. Lead weighing 0.1 kg at a temperature of 100 ° C was immersed in an aluminum calorimeter weighing 0.04 kg containing 0.24 kg of water at a temperature of 15 ° C. After that, the temperature in the calorimeter was set at 16 ° C. What is the specific heat of lead?

Heat capacity is the amount of heat absorbed by the body when heated by 1 degree.

The heat capacity of a body is indicated by a capital Latin letter WITH.

What determines the heat capacity of the body? 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.

And from the kind of substance? Let's make an experiment. Take two identical vessels and, pouring 400 g of water into one of them, and 400 g of vegetable oil into the other, we begin to heat them using identical burners. Observing the readings of the thermometers, 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, different amounts of heat are required to heat the same mass of different substances to the same temperature. The amount of heat required to heat a body and, therefore, its heat capacity depend on the kind of substance that makes up this body.

So, for example, to increase the temperature of water with a mass of 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 that shows how much heat is required to heat 1 kg of a substance by 1 ºС is called specific heat of this substance.

Each substance has its own specific heat, which is denoted by the Latin letter c and is 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 · ºС), and the specific heat capacity of ice is 2100 J / (kg · ° С); aluminum in the solid state has a specific heat equal to 920 J / (kg - ° С), and in the liquid state - 1080 J / (kg - ° С).

Note that water has a very high specific heat. Therefore, the water in the seas and oceans, warming 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, the summer is not as hot as in places far from the water.

Calculation of the amount of heat required to heat a body or emitted by it during cooling.

From the above, it is clear that the amount of heat required to heat a body depends on the kind of substance that the body consists of (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, in order to determine the amount of heat required for heating a body or released by it during cooling, you need to multiply the specific heat of the body by its mass and by the difference between its final and initial temperatures:

Q= cm (t 2 -t 1),

where Q- quantity of heat, c- specific heat, m- body mass, t 1- initial temperature, t 2- final temperature.

When the body is heated t 2> t 1 and therefore Q >0 ... When cooling the body t 2 and< t 1 and therefore Q< 0 .

If the heat capacity of the whole body is known WITH, Q determined by the formula: Q = C (t 2 - t 1).

22) Melting: determination, calculation of the amount of heat for melting or solidification, specific heat of fusion, graph of dependence t 0 (Q).

Thermodynamics

A branch of molecular physics that studies the transfer of energy, the laws governing the transformation of some types of energy into others. Unlike molecular kinetic theory, thermodynamics does not take into account the internal structure of substances and microparameters.

Thermodynamic system

It is a collection of bodies that exchange energy (in the form of work or heat) with each other or with the environment. For example, the water in the kettle cools down, the heat of the water is exchanged with the kettle and the kettle with the environment. Cylinder with gas under the piston: the piston performs work, as a result of which the gas receives energy and its macro parameters change.

Quantity of heat

it energy received or given away by the system in the process of heat exchange. It is designated by the symbol Q, it is measured, like any energy, in Joules.

As a result of various heat transfer processes, the energy that is transferred is determined in its own way.

Heating and cooling

This process is characterized by a change in the temperature of the system. The amount of heat is determined by the formula

Specific heat capacity of a substance with measured by the amount of heat required to heat mass units of this substance by 1K. Heating 1kg of glass or 1kg of water requires different amounts of energy. Specific heat is a known, already calculated value for all substances; see the value in physical tables.

Heat capacity of substance С- This is the amount of heat that is needed to heat the body without taking into account its mass by 1K.

Melting and crystallization

Melting is the transition of a substance from a solid to a liquid state. The reverse transition is called crystallization.

The energy spent on the destruction of the crystal lattice of a substance is determined by the formula

Specific heat of fusion is a known quantity for each substance, see the value in physical tables.

Vaporization (evaporation or boiling) and condensation

Vaporization is the transition of a substance from a liquid (solid) state to a gaseous one. The reverse process is called condensation.

Specific heat of vaporization is a known quantity for each substance, see the value in physical tables.

Combustion

The amount of heat that is released during the combustion of a substance

Specific calorific value is a known value for each substance, see the value in physical tables.

For a closed and adiabatically isolated system of bodies, the heat balance equation is fulfilled. The algebraic sum of the amounts of heat given off and received by all bodies participating in heat exchange is equal to zero:

Q 1 + Q 2 + ... + Q n = 0

23) The structure of liquids. Surface layer. Surface tension force: examples of manifestation, calculation, surface tension coefficient.

From time to time, any molecule can move to an adjacent vacant place. Such jumps in liquids occur quite frequently; therefore, the molecules are not attached to specific centers, as in crystals, and can move throughout the entire volume of the liquid. This explains the fluidity of fluids. Because of the strong interaction between closely spaced molecules, they can form local (unstable) ordered groups containing several molecules. This phenomenon is called short order(fig. 3.5.1).

The coefficient β is called temperature coefficient of volumetric expansion ... This coefficient for liquids is tens of times greater than that of solids. For water, for example, at a temperature of 20 ° C β in ≈ 2 10 - 4 K - 1, for steel β st ≈ 3.6 10 - 5 K - 1, for quartz glass β kv ≈ 9 10 - 6 K - 1 .

Thermal expansion of water has an interesting and important anomaly for life on Earth. At temperatures below 4 ° C, water expands with decreasing temperature (β< 0). Максимум плотности ρ в = 10 3 кг/м 3 вода имеет при температуре 4 °С.

When water freezes, it expands, so the ice remains floating on the surface of the freezing body of water. The temperature of the freezing water under the ice is 0 ° С. In denser layers of water at the bottom of the reservoir, the temperature is about 4 ° C. Thanks to this, life can exist in the water of freezing reservoirs.

The most interesting feature of liquids is the presence free surface ... Liquid, unlike gases, does not fill the entire volume of the vessel into which it is poured. An interface forms between a liquid and a gas (or vapor), which is in special conditions compared to the rest of the liquid mass .. It should be borne in mind that due to the extremely low compressibility, the presence of a more densely packed surface layer does not lead to any noticeable change in the volume of the liquid ... If the molecule moves from the surface to the interior of the liquid, the forces of intermolecular interaction will do a positive job. On the contrary, in order to pull a certain number of molecules from the depth of the liquid to the surface (i.e., to increase the surface area of the liquid), external forces must do positive work Δ A ext, proportional to the change in Δ S surface area:

It is known from mechanics that the equilibrium states of a system correspond to the minimum value of its potential energy. Hence it follows that the free surface of the liquid tends to reduce its area. For this reason, a free drop of liquid takes on a spherical shape. The fluid behaves as if forces are acting tangentially to its surface, reducing (pulling) this surface. These forces are called surface tension forces .

The presence of surface tension forces makes the surface of the liquid similar to an elastic stretched film, with the only difference that the elastic forces in the film depend on its surface area (i.e., on how the film is deformed), and the surface tension forces do not depend from the surface area of the liquid.

Some liquids, such as soapy water, tend to form thin films. Well-known soap bubbles have a regular spherical shape - this also shows the effect of surface tension forces. If a wire frame is lowered into a soapy solution, one of the sides of which is movable, then the whole of it will be covered with a film of liquid (Fig. 3.5.3).

Surface tension forces tend to shrink the film surface. To balance the movable side of the frame, an external force must be applied to it.If the force moves the crossbar by Δ x, then the work Δ A ext = F ext Δ x = Δ E p = σΔ S, where Δ S = 2LΔ x- the increment in the surface area of both sides of the soap film. Since the modules of forces and are the same, you can write:

Thus, the coefficient of surface tension σ can be defined as modulus of surface tension force acting per unit length of the surface bounding line.

Due to the action of surface tension forces in liquid drops and inside soap bubbles, an excess pressure Δ p... If you mentally cut a spherical drop of radius R into two halves, then each of them should be in equilibrium under the action of surface tension forces applied to the cut boundary with a length of 2π R and overpressure forces acting on the area π R 2 sections (Fig. 3.5.4). The equilibrium condition is written as

If these forces are greater than the forces of interaction between the molecules of the liquid itself, then the liquid wets surface of a solid. In this case, the liquid approaches the surface of the solid at a certain acute angle θ, which is characteristic of the given pair of liquid - solid. The angle θ is called edge angle ... If the forces of interaction between molecules of a liquid exceed the forces of their interaction with molecules of a solid, then the contact angle θ turns out to be obtuse (Fig. 3.5.5). In this case, they say that the liquid does not wet surface of a solid. At full wettingθ = 0, for complete non-wettingθ = 180 °.

Capillary phenomena called the rise or fall of liquid in small diameter tubes - capillaries... Wetting liquids rise through the capillaries, non-wetting liquids go down.

In fig. 3.5.6 depicts a capillary tube of a certain radius r lowered by its lower end into a wetting liquid of density ρ. The upper end of the capillary is open. The rise of liquid in the capillary continues until the force of gravity acting on the column of liquid in the capillary becomes equal in magnitude to the resulting F n surface tension forces acting along the boundary of contact of the liquid with the surface of the capillary: F t = F n, where F t = mg = ρ hπ r 2 g, F n = σ2π r cos θ.

This implies:

With complete non-wetting θ = 180 °, cos θ = –1 and, therefore, h < 0. Уровень несмачивающей жидкости в капилляре опускается ниже уровня жидкости в сосуде, в которую опущен капилляр.

Water almost completely wets the clean glass surface. Conversely, mercury does not completely wet the glass surface. Therefore, the level of mercury in the glass capillary drops below the level in the vessel.

24) Vaporization: definition, types (evaporation, boiling), calculation of the amount of heat for vaporization and condensation, specific heat of vaporization.

Evaporation and condensation. Explanation of the phenomenon of evaporation based on the concept of the molecular structure of matter. Specific heat of vaporization. Her units.

The phenomenon of the transformation of liquid into vapor is called vaporization.

Evaporation -the process of vaporization occurring from an open surface.

Liquid molecules move at different speeds. If any molecule is near the surface of a liquid, it can overcome the attraction of neighboring molecules and fly out of the liquid. The escaped molecules form vapor. The remaining liquid molecules change their velocities upon collision. In this case, some molecules acquire a speed sufficient to fly out of the liquid. This process continues, so the liquids evaporate slowly.

* Evaporation rate depends on the type of liquid. Those liquids in which molecules are attracted with less force evaporate faster.

* Evaporation can occur at any temperature. But at high temperatures, evaporation is faster. .

* Evaporation rate depends on its surface area.

* With wind (air flow), evaporation is faster.

During evaporation, the internal energy decreases, because during evaporation, fast molecules leave the liquid, therefore, the average speed of the remaining molecules decreases. This means that if there is no energy inflow from outside, then the temperature of the liquid decreases.

The phenomenon of transformation of vapor into liquid is called condensation. It is accompanied by the release of energy.

Condensation of steam is responsible for the formation of clouds. Water vapor, rising above the ground, forms clouds in the upper cold layers of the air, which consist of the smallest drops of water.

Specific heat of vaporization - physical a value that shows how much heat is needed to turn a 1 kg liquid into steam without changing the temperature.

Ud. heat of vaporization denoted by the letter L and is measured in J / kg

Ud. heat of vaporization of water: L = 2.3 × 10 6 J / kg, alcohol L = 0.9 × 10 6

The amount of heat required to convert a liquid into steam: Q = Lm

(or heat transfer).

Specific heat of a substance.

Heat capacity Is the amount of heat absorbed by the body when heated by 1 degree.

The heat capacity of a body is indicated by a capital Latin letter WITH.

What determines the heat capacity of the body? 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.

And from the kind of substance? Let's make an experiment. Take two identical vessels and, pouring water of 400 g into one of them, and 400 g of vegetable oil into the other, we begin to heat them using identical burners. Observing the readings of the thermometers, 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, to heat the same mass of different substances to the same temperature, a different amount of heat is required. The amount of heat required to heat a body and, therefore, its heat capacity depend on the kind of substance that makes up this body.

A physical quantity that shows how much heat is required to heat 1 kg of a substance by 1 ºС is called specific heat of this substance.

Each substance has its own specific heat, which is denoted by the Latin letter c and is measured in joules per kilogram-degree (J / (kg · ° C)).

Calculation of the amount of heat required to heat a body or emitted by it during cooling.

Q = cm (t 2 - t 1 ) ,

where Q- quantity of heat, c- specific heat, m- body mass , t 1 - initial temperature, t 2 - final temperature.

When the body is heated t 2> t 1 and therefore Q > 0 ... When cooling the body t 2 and< t 1 and therefore Q< 0 .

If the heat capacity of the whole body is known WITH, Q determined by the formula:

Q = C (t 2 - t 1 ) .