The amount of heat is not so simple

If you leave a cold spoon in a glass with boiling water, then after a while its temperature will be equal to the temperature of the water. The water cools down a little, and the spoon, on the contrary, heats up. The temperature at them becomes identical and comes to balance, some quantity of heat passes from more hot to more cold body.

From the point of view of the modern molecular-kinetic theory, an energy transfer to an object with a low temperature occurred from an object with a high temperature. And such a transition occurs until the temperature of both bodies is equalized, i.e. They will come to a state of thermal equilibrium. In fact, the notion of the amount of heat, which is a measure of energy transfer, has been preserved since physicists used the notion of heat.

However, this does not mean that today it is impossible to be guided by them. This concept accurately characterizes the processes occurring during heat transfer. It is customary to denote the amount of heat by the letter Q and measure it in Joules. Or else they use obsolete units of measurement - calorie and (larger) kilocalorie. Now, perhaps, we need to touch a little on what will happen to the substance when getting some energy from outside.

During heat exchange, the energy (heat) received can be spent on heating the substance or object (a teaspoon in a glass), changing its aggregate state - melting (oil in a frying pan) or vaporization (kettle on the stove). It is clear that these are different processes, and each of the described phenomena will require its own amount of energy. Scientists eventually established how it is possible to calculate the amount of heat required in each particular case.

True, here, too, everything was not so simple. In the event that the aggregate state of the substance does not change, the energy obtained is proportional to the mass of the body and the temperature difference between the interacting bodies. This should be clear from the following example. If you put a light spoon in a glass with boiling water, the spoon will quickly heat up, and if a light beaker with boiling water is put on a massive metal plate, then the temperature change of the plate can be fixed only with the help of special devices.

The described dependence does not take into account another factor - the properties of the substance itself. To describe the characteristics of the material, a special parameter is used-the so-called specific heat. This value characterizes the amount of heat that must be transferred to the substance to change its temperature by 1 ° C. Each material has this value, which characterizes the ability to take (give away) heat, its own.

If in the process of heat exchange a change in the state of the body takes place, i.e. It melts or turns into steam, in which case they say little about other things. To melt the substance, a quantity of heat called heat of fusion is supplied to it, and for the formation of steam, the heat of vaporization is given.

Instead of specific heat , the calculation uses the specific heat of fusion or vapor formation. Due to these coefficients, it is possible to find the amount of heat required to melt or vaporize a desired amount of a substance. For this, it is only necessary to multiply the value of the specific heat of fusion or vaporization by the mass of the substance. As a result, the desired amount of heat will be obtained to obtain the desired result (melting or vaporization). These factors can easily be found in the reference books.

That's how you can describe what the concept of heat quantity is, what it is related to, what is spent for, and how it is possible to determine and calculate the heat (absorbed) heat during various physical processes.