If you leave a cold spoon in a glass of boiling water, then after a while its temperature will equal the temperature of water. The water cools a little, and the spoon, on the contrary, heats up. Their temperature becomes the same and comes to equilibrium, a certain amount of heat passes from a hotter to a colder body.
From the point of view of modern molecular-kinetic theory, an energy transfer from an object with a high temperature has occurred to an object with a low temperature. And such a transition occurs until the temperature of both bodies is equal, i.e. they will come to a state of thermal equilibrium. In fact, the concept of the amount of heat, which is a measure of energy transfer, has been preserved since when physicists used such a concept as heat.
However, this does not mean that today it is impossible to be guided by it. This concept pretty accurately characterizes the processes that occur during heat transfer. The generally accepted amount of heat is denoted by the letter Q and measured in Joules. Or they still use obsolete units of measurement - calories and (larger) kilocalories. Now, probably, we need to touch a little on what will happen to the substance when it receives some energy from the outside.
During heat transfer, the energy (heat) obtained can be spent on heating a substance or object (a teaspoon in a glass), a change in its state of aggregation - melting (oil in a frying pan) or vaporization (kettle on a 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 to calculate the amount of heat required in each case.
True, here, too, everything turned out to be not so simple. In the event that the aggregate state of the substance does not change, the energy received 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 place a light spoon in a glass with boiling water, then the spoon will quickly heat up, and if you put a light glass with boiling water on a massive metal plate, then the change in temperature of the plate can only be recorded using special devices.
In the described dependence, one more factor is not taken into account - 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. For each material, this quantity characterizing the ability to receive (give) heat is different.
If, in the process of heat exchange, a change in the state of the body occurs, i.e. it melts or turns into steam, in which case they say a little about other things. To melt a substance, an amount of heat, called the heat of fusion, is supplied to it, and for the formation of steam, the heat of vaporization.
In this case, instead of the specific heat , the calculations use the specific heat of fusion or vaporization. Thanks to these coefficients, you can find the amount of heat required to melt or vaporize the right amount of substance. For this, it is only necessary to multiply the value of the coefficient of 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). The mentioned coefficients can easily be found in reference books.
This is how you can describe what the concept of the amount of heat is, what it is associated with, what it is spent on, and how you can determine and calculate the released (absorbed) heat during various physical processes.