Question

Use average bond energies to calculate delta H for the reaction of H2 and O2 to form water.

Answer 1

Answer:

ΔHrxn = - 3294.8 KJ/mol

Explanation:

• 2H2 + O2 → 2H2O

H - H                         H - O - H

H - H   +   O = O   →  H - O - H  

broken bond:

⇒ 2 bond H - H + 1 bond O = O

bond formed:

⇒ 4 bond H - O

bond energies:

∴ H - H: 436.4 KJ/mol

∴ O = O: 494 KJ/mol

∴ H - O: 482 KJ/mol

broken bond:

⇒ bond energie = 2(436.4) + 494 = 1366.8 KJ/mol

bond formed:

⇒ bond energie = 4(- 482) = - 1928 KJ/mol

• ΔHrxn = ∑ΔHproducts - ∑ΔHreagent

⇒ ΔHrxn = - 1928 KJ/mol - (1366.8 KJ/mol)

⇒ ΔHrxn = - 3294.8 KJ/mol