Why must temperature increase in an adiabatic compression?
Why must temperature decrease in an adiabatic expansion?
How come when you compress a system the particles lose heat... the system loses heat?
Internal energy E is directly proportional to Temperature. Thermal energy (at the molecular level) such as rotational, vibrational, and translational energy are considered Internal Energy, and in increase in any of those increases the temperature.
Adiabatic compression-no heat flow. From E=q + w, we can see that if q is 0, then E=W. Since work is being done on the gas, it gains internal energy, and that since E is directly proportional to T (for the reasons discussed above), the temperature increases.
Adiabatic expansion-no heat flow. From E=q+w, we can see that if q is 0, then E=W. However, w=- since the gas is doing work by expanding. It is losing internal energy or USING THAT ENERGY to do the expansion (you can also think of it as trading the internal energy for the gravitational potential energy that comes about with the expansion). Since E is directly proportional to T, a decrease in E decreases the temperature of the substance.
Just remember that internal energy E is directly proportional to T (because of the molecular energies discussed earlier, an increase in such energies will increase the temperature of the substance).
