Question

Rewrite each of the following equations for phase changes, to include the heat required for the phase change. Use values from latent heat and specific heat constant tables when necessary. Indicate whether each phase change is endothermic or exothermic.
(a) H2O(l) -> H2O(s)
(b) H2O(l) -> H2O(g)

Answer 1

Answer:

The complete equation (a) is:

$H_2O_{(l)}->H_2O_{(l)}+333.55 J/g$, and is an exothermica phase change

The complete equation (b) is:

$H_2O_{(l)}+2257J/g->H_2O_{(g)}$, and is an endothermic phase change.

Explanation:

Equation (a):

$H_2O_{(l)}->H_2O_{(l)}+333.55 J/g$, is showing a phase change from a more-energetic state (liquid) to a relative-less-energetic state (solid), that means, that in order to have the phase change, it is requiered to remove heat (energy) from the water, this is known an exothermic (releases heat).

Equation (b).

$H_2O_{(l)}+2257J/g->H_2O_{(g)}$, shows that to change from a relative-less-energetic phase (liquid) to a more-energetic one (gas), it would be needed to supply energy in order to acomplish this. And it is called endothermic (absorves heat)