# For any substance, why does temperature remain constant during change of state?

##### 1 Answer
Jun 28, 2017

Because a condition of $\text{phase equilibrium}$ applies during change of state.

#### Explanation:

For the thermodynamic processes......

${H}_{2} O \left(s\right) r i g h t \le f t h a r p \infty n s {H}_{2} O \left(l\right)$ at $0$ ""^@C and....

${H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s {H}_{2} O \left(g\right)$ at $100$ ""^@C .....

.........these occur under equilibrium conditions. Energy has to be supplied to break the (strong) bonds between the molecules of the condensed phase; for water, this so-called $\text{latent heat of fusion}$ or $\text{latent heat of vaporization}$ are quite large and reflects the degree of INTERMOLECULAR force between the individual molecules (i.e. a consequence of hydrogen bonding).