Classify the following phase changes as endothermic or exothermic.
1) liquid to solid
2) solid to liquid
3) gas to liquid
4) solid to gas
5) liquid to gas
6) gas to solid
The Correct Answer and Explanation is :
Here’s a classification of the phase changes:
1) Liquid to Solid – Exothermic
2) Solid to Liquid – Endothermic
3) Gas to Liquid – Exothermic
4) Solid to Gas – Endothermic
5) Liquid to Gas – Endothermic
6) Gas to Solid – Exothermic
Explanation
Phase changes are transitions of matter from one state to another, and they are classified based on whether they absorb or release energy.
- Endothermic processes absorb energy from the surroundings. This energy input is necessary to overcome the forces holding the particles together in their initial phase. When energy is absorbed, the particles move more freely, allowing the substance to change from a more ordered state to a less ordered one, such as from a solid to a liquid or from a liquid to a gas.
- Solid to Liquid (melting): Energy is absorbed to break the rigid structure of the solid and turn it into a liquid.
- Liquid to Gas (evaporation/boiling): Energy is required to separate the particles completely, turning a liquid into a gas.
- Solid to Gas (sublimation): The substance absorbs a large amount of energy directly, skipping the liquid phase, to transform into a gas.
- Exothermic processes release energy into the surroundings. This happens when the particles lose energy and come closer together, resulting in a more ordered structure.
- Liquid to Solid (freezing): Energy is released as the liquid molecules slow down and arrange into a structured solid.
- Gas to Liquid (condensation): Gas molecules release energy as they come together to form a liquid.
- Gas to Solid (deposition): Energy is released as a gas transforms directly into a solid without passing through the liquid phase.
The distinction between endothermic and exothermic phase changes is based on whether energy is required to increase molecular motion (endothermic) or whether energy is released as molecular motion decreases (exothermic).