The study of the physical characteristics of the gas
The history of scientific discoveries very often begins with the fact that the “right” person was in the right place at the right time. This happened with the study of gases. French physicist, chemist, engineer Serge Charles became interested in aeronautics. In this regard, it was necessary to study the dependence of pressure on air temperature. Of course, heat has always been the foremost tool of researchers. Still, a powerful, easily controlled source of energy, and always at hand. The most ancient tool of knowledge has always been a touchstone, such as "well, let's see what happens when a little warm up, and if you add ...", etc.
And what is so interesting Charles discovered in the gases? Let's do our own research. Take a glass pipe, close it tightly on one side, and place a piston inside that slides along the pipe. We’ll install a source of thermal energy next to it - a regular spirit lamp - and equip our laboratory bench with temperature and pressure gauges - because we are going to investigate the dependence of pressure on temperature. So, let's begin…
We have a certain amount of gas in the volume limited by the bottom of the cylinder and the piston. We fix the piston and heat the test gas with a spirit lamp. We write several values of the pressure Pn and temperature Tn of the gas. Analyzing the data obtained, we will see that the dependence of pressure on temperature is proportional - with increasing temperature, pressure also increases. Note that the piston is subjected to different pressures: from the outside it is atmospheric, and from the inside from heated gas. For the next experiment, remove the piston lock and see that the piston moves until the pressure is equalized. But at the same time, the volume of gas has changed, and its amount (mass) has remained the same. From this follows the conclusion that Charles received: with a constant mass and volume, the gas pressure is directly proportional to the temperature - simply and with taste.
In other words, with a constant volume from heating, the pressure increases, and with a constant pressure when heating, the volume increases. For aeronautics, this meant that when the air from the burner is heated, it expands and its volume increases, but the volume of the ball does not. This means that excess air leaves the ball and inside it remains a mass of air less than the mass of the same volume of air from the outside. The law of Archimedes is triggered, and the balloon has no choice but to fly up to the delight of the public.
But the most remarkable conclusion is that the pressure P and temperature T are interconnected by the ratio P1 / T1 = P2 / T2 = .... = Pn / Tn = CONST. It can be stated differently: P = k * T, where k is a certain gas constant. If these relations are applied to unit values of temperature, pressure, and volume, then well-known constants can be obtained. For example, the volume of gas increases when heated by 1 degree by 1/273 of the original value.
Of course, of great interest is the dependence of pressure on the temperature of substances during phase transitions, for example, of a liquid into a gas. The closest object to research of this kind is water. The vapor generated above the surface of the water is a consequence of the transition of a certain number of molecules from water to the external environment. This is hindered by two factors - surface tension forces and external pressure. Only molecules with sufficient energy potential - the equivalent of temperature - can afford to overcome them. There are two ways to achieve this potential: you can increase the energy of molecules by heating water or reduce the reaction of external pressure. The first method is confirmed by the well-known fact - heated water evaporates faster, and the second - lowers the energy threshold of molecules leaving the "parent" environment.
Back to our lab setup. We will fill the space under the piston with water, quite a bit, literally 20-40 g. Note that the piston must move freely, and the system must have a relief valve. If the water is heated, the resulting water vapor will shift the piston and free itself "a place under the sun." The space above the piston should be connected to an air source with a varying pressure, for example, install a second piston with a manually controlled stem. Now we can investigate the dependence of steam temperature on pressure. Moving the piston with the rod, we change the pressure external to the first piston. We fix the intermediate data. It will correctly fix the temperature of the steam when steady, i.e. unchanged, at least briefly, meaning. If we neglect heat exchange with the environment, then the behavior of steam is not much different from the behavior of an ideal gas.
Interestingly, even with such a primitive installation, one can also observe the dependence of the boiling point on pressure. Recall that boiling refers to the transition of a liquid into steam with the formation of bubbles throughout the entire volume of the liquid. T.O. fixing boiling is very easy. Here, too, with increasing pressure, the boiling point of the liquid increases, which means that it is easy to demonstrate a trick surprising for the uninitiated - boiling water at a temperature of only 80 degrees Celsius or, seemingly, contrary to common sense, more than 110 of the same degrees Celsius.
So after studying the behavior of gas and steam under the influence of heat sources on the substance, in the end, various heat engines were created: a steam engine, a locomobile, a steam locomotive, an internal combustion engine. And few people know that the first-born among them, of course, should be considered a balloon.