Hess's Law Problems
Hess's Law Problems
Hess's Law Problems
3A + 6B → 3D ΔH = -403 kJ/mol
E + 2F → A ΔH = -105.2 kJ/mol
C → E + 3D ΔH = +64.8 kJ/mol
Suppose the first equation is reversed and multiplied by 1/6, the second and third equations are divided by 2, and the three
adjusted equations are added. What is the net reaction and what is the overall heat of this reaction?
½D → ½A + B ΔH = +67.2 kJ/mol
½E + F → ½A ΔH = -52.6 kJ/mol
½ C → ½ E + 1½ D ΔH = +32.4 kJ/mol
F + ½C → A + B + D ΔH = +47.0 kJ/mol
2. Calculate ΔH for the reaction: C2H4 (g) + H2 (g) → C2H6 (g), from the following data.
Solution:
a. C2H4 (g) + 3 O2 (g) → 2 CO2 (g) + 2 H2O (l) ΔH = -1411. kJ (Intact)
3. Calculate ΔH for the reaction 4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g), from the following data.
Solution:
a. 2 N2 (g) + 2 O2 (g) → 4 NO (g) ΔH = 2 (-180.5 kJ) (x2)
Reyes
4. Calculate ΔH for the reaction CH4 (g) + NH3 (g) → HCN (g) + 3 H2 (g), given:
Solution:
a. NH3 (g) → 1/2 N2 (g) + 3/2 H2 (g) ΔH = ½(+91.8 kJ) (Reverse and x½)
5. Calculate ΔH for the reaction 2 Al (s) + 3 Cl2 (g) → 2 AlCl3 (s), given:
Solution:
a. 2 Al (s) + 6 HCl (aq) → 2 AlCl3 (aq) + 3 H2 (g) ΔH = -1049. kJ (Intact)
Reyes