Question

Why does the density of gas in a hot air balloon decrease as the gas is heated? A. The mass of gas increases as temperature increases. B. The volume of gas decreases as temperature increases. C. The mass of gas decreases as temperature increases. D. The volume of gas increases as temperature increases.

Answer 1

The answer is D. When heated, there is only physical process not chemical process. So the mass of the gas will not change. When heated, according to the thermal expansion, the volume will increase. And the mass is constant, so the density will decrease. Density=Mass/Volume.