Enthalpy of reaction, thermochemical equations

Question

How much energy is released when 0.40 mol C6H6(g) completely reacts with oxygen? 2C6H6(g) + 15O2(g) => 12CO2(g) + 6H2O(g) the answer is -1268 but i need help getting there

Answer 1

You need to know either the ∆Hf for each of the reactants and products, or the ∆H of the reaction.  

If you have ∆Hf reactants and products, then ∆Hrx = ∑n∆Hproducts - ∑n∆Hreactants

If you have ∆Hrx, then compute ∆H for 0.40 mole by multiplying by 0.40/2 or by 0.2