# Why might a physical change require energy?

Dec 13, 2017

#### Answer:

Well physical changes are largely changes of state....

#### Explanation:

Well physical changes are largely changes of state...i.e. a phase change, solid to liquid, liquid to gas,,,etc,, and certainly some of these processes involve the INPUT of energy.

Take evaporation...

$\text{Liquid"+Delta rarr "Vapour}$

....or sublimation...

$\text{solid"+Delta rarr "Vapour}$

....or even melting...

$\text{solid"+Delta rarr "liquid}$

These physical processes involve the breaking of bonds in the condensed phase, and thus an energy input is required. What is the energy transfer for the reverse processes, $\text{condensation}$, $\text{deposition}$, $\text{fusion}$?