When snow melts does its volume decrease or increase?

The volume of the snow decreases. This had happened because the snow is made up or comprised of water (H2O) and oxygen (O). When the snow starts melting, the air inside the snow discharges into the atmosphere and the water turn out to be a puddle on the ground. 

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.