Question

Assign each of the following as exothermic or endothermic:

a) The vaporization of liquid water (Hint : the purpose of perspiration is (i) to heat you or (ii) to cool you?)

b)Dissolving of solid LiCl in water (the temperature increases as the LiCl dissolves). Has the LiCl gained or lost chemical energy (i.e. enthalpy) in the process of dissolving? Give your reasoning.

Answer 1

A). vaporization of liquid water.

When liquid water converts into its vapor it needs the heat to do so since intermolecular force between water is higher than that of the vapor.

So when heat is absorbed we call it as endothermic.

So when water absorbs heat from surrounding then it cools us

And

b).

When we try to dissolve LiCl in water then water is warmed.

We know LiCl is made of ions Li+ and Cl- . Li+ ion will have more attraction with water than Cl- so it try to release energy in the form of heat.

Heat is given out. So the reaction is exothermic.