Question

Using the bond energies below determine the value and sign of delta H for

2H-Br + F-F → 2H-F + Br-Br

Bond energies in kJ/mol: H-Br 362 H-F 565 F-F 155 Br-Br 190

When a mole of C₅H₁₂ is combusted it reacts with 8 moles of O₂.

A. How many moles of CO₂ are produced ?

B. How many moles of H₂O are produced ?

Answer 1

Ans. 1. dH_rxn = dH_products- dH_reactants

Or, dH_rxn = [2 x bond energy, HF + bond energy, Br-Br] – [2 x bond energy, HBr + bond energy, F-F]

Or, dH_rxn = [2 x 565 kJ/mol + 190 kJ/mol] – [2 x 362 kJ/mol + 155 kJ/mol]

                = [1130 kJ/mol + 190 kJ/mol ] – [724 kJ/mol + 155 kJ/mol]

Hence, dH_rxn = + 441 kJ/ mol

Ans. 2. C₅H₁₂ + 8 O₂ --------> 5 CO₂ + 6H₂O

A. 5 moles of CO₂ produced from combustion of 1 mol of C₅H₁₂

B. 6 moles of CO₂ produced from combustion of 1 mol of C₅H₁₂