# Exo- or endothermic? Clarification required regarding a few cases

Are the following processes exothermic or endothermic?

a) When solid $KBr$ is dissolved in water, the solution gets colder.

b) Natural gas ($CH_4$) is burned in a surface.

c) When concentrated $H_2SO_4$ is added to water, the solution gets very hot.

d) Water is boiled in a teakettle.

Attempt at solution: For a), I would say that it is exothermic, since the solution gets colder, which means that it releases contained heat to the surroundings.

b) is exothermic evidently.

c) By the same reasoning, the solution is getting very hot, so it must be endothermic since it absorbs heat.

d) Not sure about this one. I would say endothermic, because the absorbed heat makes it boil.

This is what I answered, and apparently I made atleast two mistakes. So can someone explain to me the flaws in my reasoning?

## 1 Answer

I think you are confusing terms:

exothermic means that it releases heat, that is energy, because the energy of the products is lower than the one of the reagents.

endothermic means that it absorbs heat (energy) because the products are at a higher level of energy than the reagents.

When a solution becomes hot, it's because it's releasing heat (energy), and likewise if it gets cold it's because the reagents inside are absorbing energy from the surronding environment.

The case of boling water: does it need heat to become steam? Or does it release heat? In other words, do you have to provide heat to the teakettle to make the water boil or it provides heat by itself?

I hope you can get to your answers by yourself now.