Question

What is the energy change that will occur when 25.5 grams of oxygen gas (O2) react with excess methane (CH4) according to the reaction below?
CH4 + 2 O2yields CO2 + 2 H2O delta H = -889 kJ/mol

Select one:
a. 354 kJ of energy will be given off by the reaction
b. 354 kJ of energy will be absorbed by the reaction
c. 708 kJ of energy will be given off by the reaction
d. 708 kJ of energy will be absorbed by the reaction

Answer 1

Amount of CH4 is excess, so no need to worry about it 
but the limiting factor is the Oxygen 

according to stranded equation, 

CH4 + 2 O2 --> CO2 + 2 H2O ΔH = -889 kJ/mol 


just by taking proportions 

(-889 kJ/mol) / 2 x 0.8 mol = - 355.6 kJ 

so i think the answer is (a)