Question

Using the following bond energies, calculate the energy change for the reaction below.
2H^2 + O^2 -> 2H^2O
H-H 436 kJ , O=O 498 kJ , O-H 463 kJ

pls help

Answer 1

if it helps, i know that the answer is - 482 kJ, but I don't quite understand it.

Answer 2

Energy of the reaction = B.E. reactants - B.E. products.
For the reactants you break two H-H bonds and one O=O bond so that is 2*436 kJ + 498 kJ.
For the products you form 2HOH which is 2 O-H bonds per HOH mole and you have 2 HOH moles so that is 4*O-H or 4*463 kJ. Put that together from what I wrote above of
B.E. reactants - B.E. products = (2*436 + 498) - (4*463) = -482 kJ/mol. Piece o' cake!

Answer 3

Thank you so much!