Question

Indicate whether each of these reactions is endothermic or exothermic.

NH4Cl(s) es002-1.jpg NH4+(aq) + Cl–(aq) es002-2.jpgHrxn = 14.7 kJ

NaOH(s) es003-1.jpg Na+(aq) + OH–(aq) es003-2.jpgHrxn = -44.5 kJ

CH4(g) + 2O2(g) es004-1.jpg CO2(g) + 2H2O(g) es004-2.jpgHrxn < 0

CH3COOH(aq) + NaHCO3(s) es005-1.jpg CO2(g) + H2O(l) + Na+(aq) + CH3COO–(aq) es005-2.jpgHrxn > 0

Answer 1

1) NH4Cl(s) → NH4+(aq) + Cl–(aq), ΔH = +14.7 kJ → endothermic (absorbs heat)

2) NaOH(s) → Na+(aq) + OH–(aq), ΔH = −44.5 kJ → exothermic (releases heat)

3) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g), ΔH < 0 → exothermic (combustion releases heat)

4) CH3COOH(aq) + NaHCO3(s) → CO2(g) + H2O(l) + Na+(aq) + CH3COO–(aq), ΔH > 0 → endothermic (absorbs heat)