Which of the following phase changes is an exothermic change?
a) sublimation
b) deposition
c) vaporization
d) melting

The phase change that is an exothermic process is B. deposition. It is an exothermic process because it requires a release of heat to change from one phase to the other.

Some changes in state are exothermic process while others are endothermic.

Exothermic Process

Endothermic Process

A) Sublimation

Sublimation is phase change from solid to gas without passing through the liquid state. For the closely packed particles of the solid to spread out and change to its gaseous state, they must absorb heat. Therefore, this process is endothermic.

B) Deposition

This is the process of changing from gas to solid state without passing through the liquid state. For the particles of the gas to turn to solid, they must lose their energy so that when they collide with each other the attractive forces will hold them together forming the solid. This is an example of an exothermic process.

C. Vaporization

Particles of a vapor are farther away from each other than the particles of liquids. Liquids, therefore, need to be heated to turn them into gas or vapor. Since it requires absorption of heat, this is endothermic.

D. Melting

Solid particles are more closely packed than liquids. They are held by strong attractive forces that keep their movement limited to vibration in place. To change solids to liquids, their attractive forces must be overcome by heating. Absorption of heat makes the particles vibrate harder and overcome the attractive forces holding the solid together.

Keywords: phase change, exothermic , endothermic

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.