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 they both heat up - both water and a 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 capacity of water is about ten times that 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 know that it depends on chemical properties substances, 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 an air layer 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
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 an air layer 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 at all. this term. 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 have to remember 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 doesn't matter if it's Celsius, Kelvin or 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). Most great importance of this physical quantity for hydrogen is 14.300 kJ / (kg K), the smallest 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 allow you 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 - in short description information shows the answer to the question.
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).