Question

Use bond energies to estimate the heat for the combustion of 2.6 g of acetylene gas C2H2 to form carbon
dioxide and water vapor

Answer 1

First we convert 2.6 g of acetylene to mole.

molar mass of acetylene = 26.04 g/mol

mass = 2.6

moles = 2.6 / 26.04 g/mol =0.099 g/mol g/mol

The heat for the combustion of 2.6g (0.1 mol) of acetylene C2H2 to form carbon dioxide and water vapor

The bond dissociation energies:-  

BE(C–H) = 456 kJ/mol

            BE(C≡C) = 962 kJ/mol

            BE(O=O) = 499 kJ/mol

            BE(C=O) = 802 kJ/mol

            BE(O–H) = 462 kJ/mol

0.1(C2H2) + (5/2)O2 → 2CO2 + H2O

0.1(H-C C-H)+ 5/20=0 ---> 20=C=O + H-0-H

0.1[962 + (2)(456)] + (5/2)499 = (2)(2)(802) + (2)(462) + E
E = (187.4+1247.5 - 4134) kJ/mol

E = 2699.1 kJ/mol kJ/mol