chemistry question

Question

Write the balanced chemical equation for the complete combustion of gaseous pentane (C₅H₁₂) and then use bond dissociation energy data to calculate the enthalpy change for this reaction. Assume all reactants and products are in the gaseous state. Finally, state whether the reaction is endothermic or exothermic.

Answer 1

Since you didn't provide the bond dissociation energies, I won't be able to answer that part of the question, but will describe to you how to do it.

C₅H₁₂ + 8O₂ ==> 5CO₂ + 6H₂O ... balanced equation

To find enthalpy change for the reaction, sum all the bond energies of the reactants, and of the products (*) and find the difference. Recall that energy is required to break bonds (reactants) and energy is liberated upon bond formation (products). If the bond energy of the reactants is greater than the products, the reaction is endothermic. If bond energy of products is greater than reactants, the reaction is exothermic.

*For example, C₅H₁₂ has 4 C-C bonds and 12 C-H bonds. So look up the bond energy of C-C and multiply by 4. Look up bond energy for C-H and multiply by 12. Add these together to get bond energy for C5H12. Do the same for other reactant and products.