Enthalpy Practice Problems

Name ______Date ______Period _____

1. How much heat will be released when 6.44 g of sulfur reacts with excess O2 according to the following equation? 2S + 3O2 à 2SO3 ΔH = -791.4 kJ

2. How much heat will be released when 4.72 g of carbon reacts with excess oxygen according to the following equation? C + O2 à CO2 ΔH = -393.5 kJ

3. How much heat will be absorbed when 38.2 g of bromine reacts with excess hydrogen to form hydrobromic acid? ΔH= 72.80 kJ (hint – write the balanced equation for the reaction)

4. If 1.48 g of chlorine reacts with excess phosphorous to form phosphorous pentachloride, how much heat will be associated with the reaction? Will it be endothermic or exothermic? ΔH = -886 kJ

5. How much heat is released when 477 g of ethanol (C2H5OH) reacts with excess oxygen to produce carbon dioxide and water? ΔH = -1366.7 kJ

6. From the following enthalpy changes,

Xe(g) + F2(g) à XeF2(s) ∆H = -123 kJ

Xe(g) + 2F2(g) à XeF4(s) ∆H = -262 kJ

calculate the value of ∆H for the reaction

Xe F2(s) + F2 (g) à XeF4(s).

7. From the following enthalpy changes,

4NH3 (g)+ 5O2 (g) à 4NO(g) + 6H20(l) ∆H = -1170 kJ

4NH3 (g)+ 3O2 (g) à 2N2(g) + 6H20(l) ∆H = -1530 kJ

calculate the value of ∆H for the reaction

N2(g) + O2(g) à 2NO(g).

8. From the following enthalpy changes,

2Al(s) + 3/2O2(g) à Al2O3(s) ∆H = -1601 kJ

2Fe(s) + 3/2 O2(g) à Fe2O3(s) ∆H = -821 kJ

calculate the ∆H for the reaction

2Al(s) + Fe2O3(s) à 2Fe(s) + Al2O3(s).

9. From the following enthalpy changes,

H2O2(l) à H2O(l) + ½ O2(g) ∆H = -94.6 kJ

H2(g) + ½ O2 (g) à H2O(l) ∆H = -286.0 kJ

calculate the value of ∆H for the reaction

H2(g) + H2O2(l) à 2H2O(l).

10. From the following enthalpy changes,

C(s) + O2(g) à CO2(g) ∆H = -393.5 kJ

H2(g) + ½ O2(g) à H2O(l) ∆H = -285.8 kJ

2C2H2(g) + 5O2(g) à 4CO2(g) + 2H2O(l)

∆H = -2598.8 kJ

calculate the value of ∆H for the reaction

2C(s) + H2(g) à C2H2(g)