Calculating Heat Change
Heat change in a chemical reaction is directly proportional to the number of mole of reactant that takes part in a reaction or number of mole of product been produced.
Calculate the heat change when 0.1 mole of nitrogen dioxide is formed in the reaction that shown above.
How much energy is released when 4g of carbon combust completely in excess oxygen. (Relative atomic mass of carbon = 12 )
Number of mole of carbon = 4g 12gmo l −1 = 1 3 mol
Find the mass of alcohol that need to be combusted, in excess of oxygen, to release 140 kJ of heat energy.
[Relative atomic mass: H=1; C=12; 0=16]
Number of mole of alcohol = 140kJ 560kJmo l −1 =0.25mol
Relative molecular mass of CH3OH = 12 + 3(1) + 16 + 1 = 32
Mass of alcohol = 0.25mol x 32g/mol = 8g
Number of mole of copper(II) sulphate solution
n= MV 1000 n= (0.2)(50) 1000 =0.01mol
Heat change = 0.01 x 190kJ = 1.9kJ
Relative molecular mass of carbon dioxide = 12 + 2(16) = 44
Number of mole of carbon dioxide = 35.2/44 = 0.8 mol
Number of mole of carbon = 0.8 mol