In thermochemistry energy comes in two forms, which are heat and work.
Heat is defined as the change in energy. There is a change in energy when molecules of a higher temperature collide with molecules of a slower temperature. When something like gaseous nitrogen decreases in temperature the average velocity of the molecules are slowing down, which means there is a change in energy that corresponds to the amount of heat gained or lost.
The equation that relates heat and temperature is:
q = mCdeltaT
Where q is the amount of heat gain or lost. M is the mass, C is the specific heat, and deltaT is the change in temperature.
When you use this equation you want to watch the unit for. What you want to do is look at the units in the specific heat constant they give you. I looked up on Wikipedia the specific heat of gaseous nitrogen and saw that it is 1.04 J / g*K
Therefore you can do the following:
q = 10.3 * 1.04 * (295.35 - 309.15)
q = - 147.83 J or -0.14783 kJ
The negative sign means that energy was lost and went from the system to the surroundings.
