# Kinetic Theory of Gases

## Key Questions

Through the equation $Q \equiv H = n {C}_{p} \Delta T$ (for ideal gas).
For other relations for enthalpy, H, refer http://socratic.org/questions/what-is-the-formula-used-to-calculate-enthalpy#183545

#### Explanation:

Collisions of gaseous particles involves particles moving with a certain kinetic energy. And not to mention the fact that molecules possess translational, rotational, and vibrational energy. All these energies that are combined together to give enthalpy, H (This is only true for constant pressure system. For constant temperature system, internal energy, U, is the relevant variable.).

Enthalpy, H, is the relevant variable for heat because it relates to the change of temperature of the system.

• The gas expands at constant pressure because the temperature increases.

According to the KMT, a temperature increase causes an increase in the average velocity of particles. This, in turn, causes an increase in the force of impact and hence on the pressure that the particles exert on average onto the internal walls of the container.

As soon as the pressure increases, the volume increases. This causes, in turn, a reduction in the average frequency of collisions, until the pressure is restored to the initial value.

The final result is that, as the temperature increases, the volume increases in the same ratio, while the pressure is kept constant.

Very good content, nice pictures on this website: http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/kinetic.php