Question

Why is there a change in the energy of a gas when its volume changes?

Answer 1

Compressing a gas increases its motion and energy. When a gas expands, its molecules slow down, reducing its energy. In the mid-19th century, British physicist James Prescott Joule [1818-89] demonstrated that mechanical labour and the heat produced are comparable. This equivalence represents the mechanical equivalent of heat. The relationship between mechanical work W and heat produced H is W = J × H. The constant J represents the mechanical equivalent of heat (= 4.186 J/cal). Joule measured it in 1843.