There should be mass balance and the charge balance between the reactants and the products
Mass balance : total no of individual atoms of each type should be balanced before and after the reaction
Charge balance : Overall charge of the reactants should be balanced with the overall charge of the products
You can balance,
1)by just looking at it
2)by Algebraic method given above or
3)by the redox method
You need to know how to get the oxidation numbers in order to use the oxidation method
The chemical reaction would be:
C3H8 + 5O2 = 3CO2 + 4H2O
For this case, we assume that gas is ideal thus in every 1 mol the volume would be 22.41 L. We calculate as follows:
28.7 L C3H8 ( 1 mol / 22.41 L ) ( 4 mol H2O / 1 mol C3H8 ) ( 18.02 g / mol ) = 92.31 g H2O produced
Hope this answers the question.
Because of the crystal structure of the ice, ice has lower density than liquid water. So the volume of the ice of same mass is greater than water. When melting, the volume will decrease.