To investigate the dependence of pressure on temperature - there is nothing easier ...

Investigation of physical characteristics of gas

The history of scientific discoveries very often begins with the fact that the "right" person was in the right place and at the right time. So it happened with the study of gases. French physicist, chemist, engineer Serge Charles was interested in aeronautics. In this connection it was necessary to study the dependence of pressure on air temperature. Of course, heat has always been the primary tool for researchers. Still, a powerful, easily controlled source of energy, and always at hand. The most ancient instrument of cognition has always been a touchstone, like "well, well, let's see what will happen when it is a bit warm, and if you add ...", etc.

And what did Charles find interesting in gases? Let's conduct our own research. We take the glass tube, on one side it is closed tightly, and inside we arrange the piston, which slides along the pipe. We will set up a source of thermal energy - a common spirit lamp - and we will equip our laboratory stand with temperature and pressure meters , because we are going to investigate the dependence of pressure on temperature. So, let's begin…

We have some 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 the alcohol. Let us write down several values of the pressure Pn and the gas temperature Tn. Analyzing the obtained data, we see that the pressure dependence on temperature is proportional in nature - with increasing temperature, the pressure also increases. We note that the piston undergoes different pressures: from the outside it is atmospheric, and from the inside, from the heated gas. For the next experiment, remove the piston retainer and see that the piston will move to equalize the pressures. But at the same time the volume of gas changed, and its quantity (mass) remained the same. Hence follows the conclusion that Charles received: with the mass and volume unchanged, the gas pressure is directly proportional to temperature - unpretentiously and tastefully.

In other words, at a constant volume from heating, the pressure increases, and at constant pressure, when heated, the volume increases. For aeronautics, this means that when the air is heated from the burner, it expands and its volume increases, and the volume of the ball does not. Hence, the 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 works, and nothing remains for the ball, how to fly for the joy of the public.

But the most remarkable conclusion is that the pressure P and temperature T are related to each other by the relation P1 / T1 = P2 / T2 = .... = Pn / Tn = CONST. It can be stated differently: P = k * T, where k is a certain gas constant. If we apply these relations to unit values of temperature, pressure, and volume, we can obtain well-known constants. For example, the volume of the gas increases with heating 1 degree per 1/273 of the initial value.

Of course, great interest is caused by the dependence of pressure on the temperature of substances during phase transitions, for example, liquids in a gas. The closest object for research of this kind is water. The vapor that forms above the surface of water is a consequence of the transition of a certain number of molecules from water to the external medium. This is hampered by two factors - surface tension forces and external pressure. They can only be overcome by molecules with sufficient energy potential - the equivalent of temperature. There are two ways to achieve this potential: you can increase the energy of molecules by heating water or reduce the counteraction of external pressure. The first method is confirmed by a well-known fact - heated water evaporates faster, and the second - reduces the energy threshold of molecules leaving the "parent" environment.

Let's return to our laboratory installation. Space under the piston fill with water, very little, literally 20-40 g. Note that the piston must move freely, and the system must have a dump valve. If the water is heated, the formed water vapor will move the piston and release its "place under the sun". Space above the piston should be connected to a source of air with varying pressure, for example, install a second piston with a manually operated rod. Now we can investigate the dependence of vapor temperature on pressure. Moving the piston with the rod, we change the external pressure for the first piston. Intermediate data are fixed. It is correct to fix the temperature of the steam at steady state, i.e. Constant, at least for a short time, meaning. If we neglect heat exchange with the environment, then the behavior of the vapor does not differ much from the behavior of the ideal gas.

It is interesting that even on such a primitive setup one can observe the dependence of the boiling point on the pressure. Recall that boiling is called the transition of liquid into vapor with the formation of bubbles throughout the volume of the liquid. Thus. Fix the boil very easily. And here, also with increasing pressure, the temperature of boiling of the liquid increases, which means it is easy to demonstrate the amazing trick for uninitiated - boiling water at a temperature of only 80 degrees Celsius or, seemingly contrary to common sense, more than 110 same Celsius degrees.

So after studying the behavior of the gas, steam under the influence of heat sources on the substance, in the end, various thermal machines were created: a steam engine, a locomobile, a locomotive, an internal combustion engine. And very few people know that the first-born among them, of course, should be considered a balloon.