1. The problem statement, all variables and given/known data All the substances involved in the reaction given below can undergo combustion reaction and their combustion enthalpies at 300K are given below, 2A(g)+B(g) ----> 3C(g) + D(g) Given: ΔH A = -1000cal/mol ΔH B= -2000cal/mol ΔH C=-500 cal/mol ΔH D = -100 cal/mol If the reaction occurs at constant volume at 300K and the reaction obeys first order with respect to A and if A reduces to half its initial amount in 69.3 sec, then calculate 1) heat released when 2*10-3 mole of A has reacted at 300K(in cal) 2) rate at which heat is released initially, if initially 1mol of A is present. 3. The attempt at a solution ΔH of rxn = 2400 cal/mol ΔH = ΔU + Δng RT Since the reaction occurs at constant volume ΔQ = ΔU ΔQ = ΔH - Δng RT Substituting appropriate values , I get ΔQ = 1800 cal/mol. But this is not the correct answer.