Question

Given the equation representing a phase change at equilibrium:

H2O (s) <--> H2O (l)
Which statement describes this equilibrium?
A. The H2O (s) melts fadter than the H2O (l) freezes
B. The H2O (l) freezes faster than the H2O melts
C. The mass of H2O (s) must equal the mass of H2O (l)
D. The mass of H2O (l) and the mass of H20 (s) each remain constant.

Answer 1

The answer would be D, because in an equilibrium rxn, the rate of rxn remains constant. So, both reactants and products are being produced at the same rate. This means mass of both will remain constant.

Answer 2

D. The mass of H2O (l) and the mass of H20 (s) each remain constant.

Step-by-step explanation:

Equilibrium refers to a state in which the rate of the forward reaction equals the rate of the reverse reaction. Rate of a reaction is essentially the change in concentration over time. Therefore, when a system reaches equilibrium this implies that the reaction has a reached a stage where the concentrations of the reactants and products do not change anymore.

Here we have an equilibrium between ice and liquid water.

`H_(2)O(s) \rightleftharpoons H_(2)O(l)`

i.e. the rate of conversion of ice to liquid water is equal to the rate of conversion of water into ice. This does not suggest that at equilibrium the masses or the amounts of reactants will be equal to the products instead the masses will be constant i.e. it will remain unchanged.