The specific heat capacity of a substance according to the graph. Specific heat capacity of gases and vapors
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Initial value
Converted value
joule per kilogram per kelvin joule per kilogram per °C joule per gram per °C kilojoule per kilogram per kelvin kilojoule per kilogram per °C calorie (IT) per gram per °C calorie (IT) per gram per °F calorie ( thr.) per gram per °C kilocalorie (th.) per kg per °C calorie (th.) per kg per °C kilocalorie (th.) per kg per kelvin kilocalorie (th.) per kg per kelvin kilogram per kelvin pound-force foot per pound per °Rankine BTU (th) per pound per °F BTU (th) per pound per °F BTU (th) per pound per °Rankine BTU (th) per pound per °Rankine BTU (IT) per pound per °C centigrade warm units per pound per °C
Mass concentration in solution
More about specific heat capacity
General information
Molecules move under the influence of heat - this movement is called molecular diffusion. The higher the temperature of a substance, the faster the molecules move and the more intense diffusion occurs. The movement of molecules is affected not only by temperature, but also by pressure, the viscosity of a substance and its concentration, diffusion resistance, the distance that molecules travel during their movements, and their mass. For example, if we compare how the diffusion process occurs in water and in honey, when all other variables, except for viscosity, are equal, then it is obvious that the molecules in water move and diffuse faster than in honey, since honey has a higher viscosity.
Molecules need energy to move, and the faster they move, the more energy they need. Heat is one of the types of energy used in this case. That is, if a certain temperature is maintained in a substance, then the molecules will move, and if the temperature is increased, then the movement will accelerate. Energy in the form of heat is obtained by burning fuel, for example natural gas, coal, or wood. If several substances are heated using the same amount of energy, then some substances are likely to heat up faster than others due to more intense diffusion. Heat capacity and specific heat capacity describe just these properties of substances.
Specific heat determines how much energy (that is, heat) is required to change the temperature of a body or substance of a certain mass by a certain amount. This property is different from heat capacity, which determines the amount of energy required to change the temperature of an entire body or substance to a certain temperature. Heat capacity calculations, unlike specific heat capacity, do not take into account mass. Heat capacity and specific heat capacity are calculated only for substances and bodies in a stable state of aggregation, for example, for solids. This article discusses both of these concepts, as they are interrelated.
Heat capacity and specific heat capacity of materials and substances
Metals
Metals have a very strong molecular structure, since the distance between molecules in metals and other solids is much smaller than in liquids and gases. Due to this, the molecules can only move over very small distances, and, accordingly, in order to make them move at a higher speed, much less energy is needed than for the molecules of liquids and gases. Due to this property, their specific heat capacity is low. This means that it is very easy to raise the temperature of the metal.
Water
On the other hand, water has a very high specific heat capacity, even compared to other liquids, so it takes much more energy to heat one unit mass of water by one degree, compared to substances whose specific heat capacity is lower. Water has a high heat capacity due to the strong bonds between the hydrogen atoms in the water molecule.
Water is one of the main components of all living organisms and plants on Earth, therefore its specific heat capacity plays big role for life on our planet. Due to the high specific heat capacity of water, the temperature of the fluid in plants and the temperature of the cavity fluid in the body of animals change little even on very cold or very hot days.
Water provides a sustenance system thermal regime both in animals and plants, and on the surface of the Earth as a whole. A huge part of our planet is covered with water, so it is water that plays a big role in regulating weather and climate. Even with a large amount of heat coming from the impact of solar radiation on the Earth's surface, the temperature of the water in the oceans, seas and other bodies of water increases gradually, and the ambient temperature also changes slowly. On the other hand, the effect on temperature of the intensity of heat from solar radiation is large on planets where there are no large surfaces covered with water, such as the Earth, or in regions of the Earth where water is scarce. This is especially noticeable if you look at the difference between day and night temperatures. So, for example, near the ocean, the difference between day and night temperatures is small, but in the desert it is huge.
The high heat capacity of water also means that water not only heats up slowly, but also cools slowly. Due to this property, water is often used as a refrigerant, that is, as a coolant. In addition, the use of water is beneficial due to its low price. In countries with cold climates hot water circulates in pipes for heating. Mixed with ethylene glycol, it is used in car radiators to cool the engine. Such liquids are called antifreeze. The heat capacity of ethylene glycol is lower than the heat capacity of water, so the heat capacity of such a mixture is also lower, which means that the efficiency of a cooling system with antifreeze is also lower than systems with water. But this has to be put up with, since ethylene glycol does not allow water to freeze in winter and damage the channels of the car's cooling system. More ethylene glycol is added to coolants designed for colder climates.
Heat capacity in everyday life
Other things being equal, the heat capacity of materials determines how quickly they heat up. The higher the heat capacity, the more energy is needed to heat this material. That is, if two materials with different heat capacities are heated with the same amount of heat and under the same conditions, then a substance with a lower heat capacity will heat up faster. Materials with a high heat capacity, on the contrary, heat up and give off heat back to environment slower.
Kitchen utensils and utensils
Most often we choose materials for dishes and kitchen utensils based on their heat capacity. This mainly applies to items that are in direct contact with heat, such as pots, plates, baking dishes, and other similar utensils. For example, for pots and pans, it is better to use materials with a low heat capacity, such as metals. This helps the heat to transfer more easily and quickly from the heater through the pot to the food and speeds up the cooking process.
On the other hand, since materials with a high heat capacity retain heat for a long time, they are good to use for insulation, that is, when it is necessary to keep the heat of the products and prevent it from escaping into the environment or, conversely, to prevent the heat of the room from heating the chilled products. Most often, such materials are used for plates and cups in which hot or, conversely, very cold food and drinks are served. They help not only to keep the temperature of the product, but also prevent people from getting burned. Dishes made of ceramics and expanded polystyrene - good examples the use of such materials.
Heat insulating food
Depending on a number of factors, such as the content of water and fat in products, their heat capacity and specific heat capacity can be different. In cooking, knowledge of the heat capacity of foods makes it possible to use some foods for insulation. If you cover other food with insulating products, they will help this food to keep warm longer under them. If the dishes under these heat-insulating products have a high heat capacity, then they slowly release heat into the environment anyway. After they warm up well, they lose heat and water even more slowly thanks to the insulating products on top. Therefore, they stay hot longer.
An example of a thermal insulating product is cheese, especially on pizza and other similar dishes. Until it melts, it allows water vapor to pass through, which allows the food underneath to cool quickly, as the water it contains evaporates and in doing so cools the food it contains. The melted cheese covers the surface of the dish and insulates the food underneath. Often under the cheese are foods with a high water content, such as sauces and vegetables. Because of this, they have a high heat capacity and keep warm for a long time, especially because they are under melted cheese, which does not release water vapor to the outside. That's why pizza out of the oven is so hot that you can easily burn yourself with sauce or vegetables, even when the dough around the edges has cooled down. The surface of the pizza under the cheese does not cool for a long time, which makes it possible to deliver the pizza to your home in a well-insulated thermal bag.
Some recipes use sauces in the same way as cheese to insulate the food underneath. The higher the fat content in the sauce, the better it isolates the products - sauces based on butter or cream are especially good in this case. This is again due to the fact that fat prevents the evaporation of water and, therefore, the removal of the heat required for evaporation.
In cooking, materials that are not suitable for food are also sometimes used for thermal insulation. Cooks in Central America, the Philippines, India, Thailand, Vietnam and many other countries often use banana leaves for this purpose. They can not only be collected in the garden, but also bought in a store or on the market - they are even imported for this purpose in countries where bananas are not grown. Sometimes aluminum foil is used for insulation purposes. Not only does it prevent water from evaporating, but it also helps keep heat inside by preventing heat transfer in the form of radiation. If you wrap the wings and other protruding parts of the bird in foil when baking, the foil will prevent them from overheating and burning.
Cooking food
Foods with a high fat content, such as cheese, have a low heat capacity. They heat up more with less energy than high heat capacity products and reach temperatures high enough for the Maillard reaction to occur. The Maillard reaction is chemical reaction, which occurs between sugars and amino acids, and changes the taste and appearance products. This reaction is important in some cooking methods, such as baking bread and confectionery from flour, baking products in the oven, as well as for frying. To increase the temperature of the food to the temperature at which this reaction occurs, high-fat foods are used in cooking.
Sugar in cooking
The specific heat capacity of sugar is even lower than that of fat. Since sugar quickly heats up to temperatures higher than the boiling point of water, working with it in the kitchen requires safety precautions, especially when making caramel or sweets. Extreme care must be taken when melting the sugar to avoid spilling it on bare skin, as the temperature of the sugar reaches 175° C (350° F) and the burn from the melted sugar will be very severe. In some cases it is necessary to check the consistency of the sugar, but this should never be done with bare hands if the sugar is heated. Often people forget how quickly and how much sugar can heat up, which is why they get burned. Depending on what the melted sugar is for, its consistency and temperature can be checked using cold water as described below.
The properties of sugar and sugar syrup change depending on the temperature at which it is cooked. Hot sugar syrup can be thin, like the thinnest honey, thick, or somewhere in between thin and thick. Recipes for sweets, caramels, and sweet sauces usually specify not only the temperature to which the sugar or syrup should be heated, but also the hardness stage of the sugar, such as the "soft ball" stage or the "hard ball" stage. The name of each stage corresponds to the consistency of the sugar. To determine the consistency, the confectioner drops a few drops of syrup into ice water, cooling them. After that, the consistency is checked by touch. So, for example, if the chilled syrup thickens, but does not harden, but remains soft and you can make a ball out of it, then it is considered that the syrup is in the “soft ball” stage. If the shape of the frozen syrup is very difficult, but still can be changed by hand, then it is in the “hard ball” stage. Confectioners often use a food thermometer and also check the consistency of sugar by hand.
food safety
Knowing the heat capacity of foods, you can determine how long they need to be cooled or heated in order to reach a temperature at which they will not spoil and at which bacteria harmful to the body die. For example, to reach a certain temperature, foods with a higher heat capacity take longer to cool or heat than foods with a low heat capacity. That is, the duration of cooking a dish depends on what products are included in it, and also on how quickly water evaporates from it. Evaporation is important because it requires a lot of energy. Often, a food thermometer is used to check the temperature of a dish or the food in it. It is especially convenient to use it during the preparation of fish, meat and poultry.
microwaves
How efficiently food is heated in a microwave oven depends, among other factors, on the specific heat of the food. The microwave radiation generated by the microwave oven's magnetron causes the molecules of water, fat and some other substances to move faster, causing the food to heat up. Fat molecules are easy to make move due to their low heat capacity, and therefore fatty food is heated to more high temperatures than food containing a lot of water. The temperature reached may be so high that it is sufficient for the Maillard reaction. Products with a high water content do not reach such temperatures due to the high heat capacity of water, and therefore the Maillard reaction does not occur in them.
The high temperatures reached by microwave fat can cause some foods, such as bacon, to be cooked through, but these temperatures can be dangerous when used. microwave ovens, especially if you do not follow the rules for using the oven, described in the instruction manual. For example, when reheating or cooking fatty foods in the oven, you should not use plastic utensils, as even microwave utensils are not designed for the temperatures that fat reaches. Also, do not forget that fatty foods are very hot, and eat them carefully so as not to burn yourself.
Specific heat capacity of materials used in everyday life
Do you find it difficult to translate units of measurement from one language to another? Colleagues are ready to help you. Post a question to TCTerms and within a few minutes you will receive an answer.
Change 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 this process. The change in the internal energy of a body during heat transfer is characterized by a quantity called the amount of heat.
is the change in the internal energy of the body in the process of heat transfer without doing work. The amount of heat is denoted by the letter Q .
Work, internal energy and the amount of heat are measured in the same units - joules ( J), like any other form of energy.
In thermal measurements, a special unit of energy, the calorie ( feces), equal to the amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius (more precisely, from 19.5 to 20.5 ° C). This unit, in particular, is currently used in calculating the consumption of heat (thermal energy) in apartment buildings. Empirically, the mechanical equivalent of heat has been established - the ratio between calories and joules: 1 cal = 4.2 J.
When a body transfers a certain amount of heat without doing work, its internal energy increases, if a body gives off a certain amount of heat, then its internal energy decreases.
If you pour 100 g of water into two identical vessels, and 400 g into another at the same temperature and put them on the same burners, then the water in the first vessel will boil earlier. Thus, the greater the mass of the body, the large quantity It needs heat to warm up. The same goes for cooling.
The amount of heat required to heat a body also depends on the kind of substance from which this body is made. This dependence of the amount of heat required to heat the body on the type of substance is characterized by a physical quantity called specific heat capacity substances.
- this is a physical quantity equal to the amount of heat that must be reported to 1 kg of a substance to heat it by 1 ° C (or 1 K). The same amount of heat is given off by 1 kg of a substance when cooled by 1 °C.
Specific heat denoted by the letter With. The unit of specific heat capacity is 1 J/kg °C or 1 J/kg °K.
The values of the specific heat capacity of substances are determined experimentally. Liquids have a higher specific heat capacity than metals; Water has the highest specific heat capacity, gold has a very small specific heat capacity.
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 1 °C. In particular, the internal energy of 1 kg of lead, when it is heated by 1 °C, increases by 140 J, and when it is cooled, it decreases by 140 J.
Q required to heat the body mass m temperature t 1 °С up to temperature t 2 °С, is equal to the product of the specific heat of the substance, body mass and the difference between the final and initial temperatures, i.e.Q \u003d c ∙ m (t 2 - t 1)
According to the same formula, the amount of heat that the body gives off when cooled is also calculated. 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 synopsis on the topic. "Quantity of heat. Specific heat". Choose next steps:
- Go to the next abstract:
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 effects 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 indicated before, physical meaning Such a value of 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
Specific heat capacity is the energy required to increase the temperature of 1 gram of a pure substance by 1°. The parameter depends on chemical composition and state of aggregation: gaseous, liquid or solid. After his discovery, a new round of development of thermodynamics began, the science of energy transition processes that relate to heat and the functioning of the system.
Usually, specific heat capacity and the basics of thermodynamics are used in the manufacture radiators and systems designed for cooling vehicles, as well as in chemistry, nuclear engineering and aerodynamics. If you want to know how the specific heat capacity is calculated, then check out the proposed article.
Before proceeding with the direct calculation of the parameter, you should familiarize yourself with the formula and its components.
The formula for calculating the specific heat capacity is as follows:
- с = Q/(m*∆T)
Knowledge of the quantities and their symbolic designations used in the calculation is extremely important. However, it is necessary not only to know their visual appearance, but also to clearly understand the meaning of each of them. The calculation of the specific heat capacity of a substance is represented by the following components:
ΔT is a symbol denoting a gradual change in the temperature of a substance. The symbol "Δ" is pronounced like a delta.
ΔT = t2–t1, where
- t1 is the primary temperature;
- t2 is the final temperature after the change.
m is the mass of the substance used for heating (g).
Q - the amount of heat (J / J)
Based on CR, other equations can be derived:
- Q \u003d m * cp * ΔT - the amount of heat;
- m = Q/cr * (t2 - t1) - the mass of the substance;
- t1 = t2–(Q/цp*m) – primary temperature;
- t2 = t1+(Q/цp*m) – final temperature.
Instructions for calculating the parameter
- Take calculation formula: Heat capacity = Q/(m*∆T)
- Write out the original data.
- Plug them into the formula.
- Do the calculation and get the result.
As an example, let's calculate an unknown substance weighing 480 grams and having a temperature of 15ºC, which, as a result of heating (supplying 35 thousand J), increased to 250º.
According to the instructions given above, we perform the following actions:
We write out the initial data:
- Q = 35 thousand J;
- m = 480 g;
- ΔT = t2–t1 = 250–15 = 235 ºC.
We take the formula, substitute the values and solve:
с=Q/(m*∆T)=35 thousand J/(480 g*235º)=35 thousand J/(112800 g*º)=0.31 J/g*º.
Calculation
Let's perform the calculation C P water and tin under the following conditions:
- m = 500 grams;
- t1 =24ºC and t2 = 80ºC - for water;
- t1 =20ºC and t2 =180ºC - for tin;
- Q = 28 thousand J.
First, we determine ΔT for water and tin, respectively:
- ΔTv = t2–t1 = 80–24 = 56ºC
- ΔТо = t2–t1 = 180–20 =160ºC
Then we find the specific heat capacity:
- c \u003d Q / (m * ΔTv) \u003d 28 thousand J / (500 g * 56ºC) \u003d 28 thousand J / (28 thousand g * ºC) \u003d 1 J / g * ºC.
- с=Q/(m*ΔТо)=28 thousand J/(500 g*160ºC)=28 thousand J/(80 thousand g*ºC)=0.35 J/g*ºC.
Thus, the specific heat capacity of water was 1 J/g*ºC, and that of tin was 0.35 J/g*ºC. From this we can conclude that with an equal value of the input heat of 28 thousand J, the tin will heat up faster than water because its heat capacity is less.
Heat capacity is not limited to gases, liquids and solid bodies but also food.
How to calculate the heat capacity of food
When calculating the power capacity the equation will take the following form:
c=(4.180*w)+(1.711*p)+(1.928*f)+(1.547*c)+(0.908*a), where:
- w is the amount of water in the product;
- p is the amount of proteins in the product;
- f- percentage fats;
- c is the percentage of carbohydrates;
- a is the percentage of inorganic components.
Determine the heat capacity of processed cream cheese Viola. For this we write out desired values from the composition of the product (weight 140 grams):
- water - 35 g;
- proteins - 12.9 g;
- fats - 25.8 g;
- carbohydrates - 6.96 g;
- inorganic components - 21 g.
Then we find with:
- c=(4.180*w)+(1.711*p)+(1.928*f)+(1.547*c)+(0.908*a)=(4.180*35)+(1.711*12.9)+(1.928*25 .8) + (1.547*6.96)+(0.908*21)=146.3+22.1+49.7+10.8+19.1=248 kJ/kg*ºC.
Always remember that:
- the process of heating the metal is faster than that of water, since it has C P 2.5 times less;
- if possible, transform the results obtained into more high order if conditions permit;
- in order to check the results, you can use the Internet and look with for the calculated substance;
- under equal experimental conditions, more significant temperature changes will be observed in materials with low specific heat.
