Why does the temperature rise during adiabatic compression

Big Bang, high school graduation

94 Register 32d: At If the temperature does not change during compression, then the point that shows the current state of the gas moves vertically upwards. If the temperature is below the temperature at the triple point, the gas solidifies without first becoming liquid. When T is above the triple point, the gas becomes liquid. If the temperature is above the critical temperature, no phase transition is possible. However, one cannot actually speak of a gas beforehand, because liquids and gases can no longer be differentiated above the critical point. 32e: If you start with water (a) in the solid phase and increase the pressure, the ice melts. Ice must therefore have a higher volume. With normal substances (b) it is exactly the opposite. If you start in the liquid phase and increase the pressure, they will solidify. Therefore, the solid phase must have a smaller volume. Question 33 33a: At the same pressure (isobaric change of state), V ~ T applies. The volume of an ideal gas is proportional to its absolute temperature. This is called Charles' Law or Gay-Lussac's Law. The straight line will therefore intersect the x-axis at the absolute zero point. Is it really possible to cool the gas so far that it has a volume of 0? No! It becomes liquid or solid beforehand and if not, the molecules will influence each other. The important thought, however, is that at room temperature all gases behave as if their volume would disappear at 0K. 33b: At the same temperature (isothermal change of state) p ~ 1 / V and thus p · V is constant. The pressure of an ideal gas is inversely proportional to the volume. This is called Boyle-Mariotte's Law. If you bring the lung volume to 4l at a depth of 30m, the bottle delivers four times as much air as on the surface. If you then emerged without exhaling, the lungs would theoretically expand to 16 liters. Of course, that is completely impossible. You would probably suffer a ruptured lung after just a few meters. 33c: Real gases can be described very well with Boyle-Mariotte's law if the temperature is far enough above the critical temperature T k. Isotherms that are close to T k are already somewhat dented (T 1). If the temperature falls below T k, a reduction in volume leads to condensation. The pressure does not rise until all of the gas has liquefied. The critical temperature for nitrogen (N 2) is –145 ° C and for oxygen (O 2) at –117 ° C, which is extremely low. Air can therefore be regarded as an ideal gas under normal conditions. In the case of carbon dioxide (CO 2), T k is + 31 ° C and in the case of water vapor it is even + 374 ° C. Here Boyle-Mariotte's law can only be applied at correspondingly high temperatures. 33c: Why do canned glass pops? Because there is a negative pressure inside, which is equalized when it is opened. How does the negative pressure come about? Because the temperature is higher when filling! When it cools down, an isochoric change of state takes place (with the same volume). When the temperature drops from 70 ° C to 20 ° C, a force of around 110N is generated in a can with a 5cm lid radius. That's the way it is, so there would be around 11kg on the can that you have to lift when unscrewing it. Question 34 34a: The general gas law says the following: You cannot choose the pressure, temperature and volume of a gas arbitrarily. Its state is fixed when two of the values ​​are fixed. The values ​​are therefore on a three-dimensional surface. The gas laws for special conditions are the two-dimensional projections of them. In order to get from the general gas law to a general gas equation, one has to determine the third experimentally if two quantities are known. A constant (R) is then obtained which is valid for all gases. 34b: A compression in which there is no heat exchange is called adiabatic, and the resulting pressure is higher than expected. Only when the generated heat has dissipated does the pressure drop to the expected value. The reverse also applies: if you increase the volume quickly, the temperature drops. That is an adiabatic expansion. Therefore, an adiabatic is steeper than an isotherm (see figure on the right). 34c: The air pressure decreases with altitude and therefore the air expands when it rises. Because air is a poor conductor of heat, it expands adiabatically and cools down by 1 ° C for every 100 meters of altitude. 34d: The expansion initially makes the gas colder, and the compression (depression) warms it up again. Both effects are the same, however. The warming can only be explained by the heat of condensation that is released when clouds form on the south side of the Alps. Foehn on the north side is always associated with cloud formation on the south side. 34e: If the piston is knocked down with the palm of the hand and the air is compressed very quickly, an adiabatic change of state takes place. The energy released in the process warms the air, and the heat cannot be released to the outside due to the rapid compression. There must be a highly flammable material inside. Even when inflating a bicycle tire, the inside of the pump becomes warm due to the adiabatic compression. Question 35 35a: A decrease in temperature would mean a decrease in the entropy in the room. The 2nd law of thermodynamics forbids this. So it is not possible to cool the room with the ice box. The law of energy says that the number of joules always remains the same. But now joules flow into your room with the energy of the current. So the room will even warm up! An ice box produces more heat on the back than it extracts inside. 35b: You can put the ice box in the window with the back facing outwards and seal it all around. It's getting colder inside, warmer outside. The room is no longer a closed system. 35c: Heat only flows by itself to places with lower temperatures. An ice chest or an air conditioning system are able to transport heat from a colder place (inside) to a warmer place (outside), i.e. against the natural flow direction. This is commonly called a heat pump. These are also used for heating. Heat is extracted from the groundwater. Ten meters below the surface of the earth, the temperature is around 10 ° C even in the cold season. If a liquid fluid that is sensitive to excess pressure (for example propane boiling point 56 ° C at 20 bar, –25 ° C at 2 bar) is brought into the ground via the expansion valve through thin metal pipes after the pressure has been released, it absorbs geothermal energy and evaporates. It is then compressed and can now liquefy again in the condenser by releasing heat to the heating system of the house. The cycle is closed. Because the heating water temperature is only around 45 ° C, it is referred to as low-temperature heating. This only makes sense in combination with underfloor heating, because normal central heating requires a water temperature of at least 60 ° C. The advantage of the heat pump: You need a certain amount of work to operate it and you get the pumped heat for free, so to speak! That is why it is more efficient than normal central heating. 35d: Central heating heats the apartment and does nothing else. A heat pump heats the apartment, but at the same time cools something else down. It's a completely different principle. 35e: The flow diagram shows that the heat Q 2 is greater than the outflowing heat Q 1. In other words: more heat comes out at the back than flows out inside. For testing purposes only - property of the publisher öbv

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