Question

Hydrogen burns exothermically in oxygen

What is the energy given out during the reaction: 2H2 + O2 -> 2H2O?

Given:
H-H bond: 436 kJ/mol
O=O double bond: 498 kJ/mol
O-H bond: 464 kJ/mol

A. -3226 kJ/mol
B. -884 kJ/mol
C. -486 kJ/mol
D. -442 kJ/mol​

Answer 1

C. -486 kJ/mol

Step-by-step explanation:

Enthalpy change equals bonds broken (reactants) minus bonds formed (products)

Bonds broken = 2 H-H bonds + 1 O=O double bond = 2(436) +498 = 1,370 kJ/mol

Bonds formed = 4 O-H bonds = 4(464) = 1,856 kJ/mol

Bonds broken - bonds formed = 1,370 - 1,856 = -486 kJ/mol