The following processes occur spontaneously at 25 °C. Which of these processes are endothermic?

Question

The following processes occur spontaneously at 25 °C. Which of these processes are endothermic?

1.the combustion of methane to produce water and carbon dioxide
2.the expansion of an ideal gas into a vacuum
3.the melting of ice

a.3 only
b.2 and 3
c.2 only
d.1 and 2

Answer 1

a. 3 only - it is absorbing energy just to break the crystal lattice to change from solid(ice) to liquid(water). The water is then absorbing more energy just to raise its temp'r from 0degreesC
to 25 degreesC So it is endothermic.

If a substance is being combusted it is releasing energy(heat) so it is exothermic.
If a gas is allowed to Expand it neither gains nor loses energy. the molecules just move further apart under the energy they already possess.