How are states of matter and changes in energy related?

1 Answer
Jul 18, 2018

I'm not a chemistry major, so here's the brief explanation:


Matter comes in 4 states -- solid, liquid, gas(eous) and plasma, but not every element or compound exists naturally in each state.

Water is pretty special in that it's the "only substance on Earth that occurs naturally as a liquid, a solid, and a gas."

(see Physical Geography , Peterson, Sack, and Gabbler, 10th Ed., p. 137)

(If this were not the case, life would not be able to exist on Earth.)

Water's chemical formula is H2O regardless of which state it's in, because change of state is a physical, not a chemical, change.

Energy is involved in changes of state.

Water needs heat (energy) to go from a solid (ice) to liquid water, and more energy/heat to go from there to water vapor (gas).

Water releases heat when it goes in the other direction.

"Evaporation is endothermic -- heat is absorbed when a liquid is converted into a gas because energy is required to break a molecule away from the rest of the liquid."


"Condensation, the opposite of evaporation, is exothermic --heat is released when a gas condenses to a liquid."

(Introductory Chemistry , Nivaldo Tro, 3rd edition, p. 416.)

P.S., This is a really good chem book for an Intro course.