The combustion of one mole of benzene, C6H6, in oxygen releases 3268 kJ of heat. The products of the reaction are carbon dioxide and water.

Question

a) Write the balanced thermochemical equation for the combustion of 1 mole of benzene.

b) Is the reaction exothermic or endothermic?

c) How much heat (in kJ) is given off when 106.4 g of benzene are burned? Remember to use the correct sign in your answer!

Answer 1

a) C₆H₆ + 7.5 O₂ ==> 6CO₂ + 3H₂O + heat ∆H = -3268kJ/mol ... balanced equation for 1 mol C₆H₆

b) The reaction is exothermic as indicated by the production of heat

c) molar mass C₆H₆ = 78 g/mol

moles C₆H₆ used = 106.4 g x 1 mol/78 g = 1.36 moles

heat given off = 1.36 moles x -3268 kJ/mol = -4458 kJ (notice the negative sign because heat is given off, i.e. the reaction is exothermic, so the sign must be negative)