Tutorial 5: Chapter 5 Chemical Energetics / Thermochemistry
1. A 9.36 g of platinum is heated to 98.6 °C and dropped onto ice. When the metal’s temperature has dropped to 0.0 °C, it is found that 0.37 g of ice has melted. Determine the specific heat capacity of platinum. (Given the latent heat of fusion for ice is 333 J g
-1
.)
2. A 72.8 g of copper at 143.2 °C is added to an insulated vessel containing 165 mL of glycerol (density = 1.26 g mL-1
), at 24.8 °C. The final temperature is 31.1 °C. The specific heat capacity of copper is 0.385 J g-1
°C-1
.
(a) Determine the mass of glycerol.
(b) Determine the heat released from the copper.
(c) Determine the specific heat capacity of glycerol in J g-1
°C-1
. (Ans: 2.4 J g-1
°C-1
)
[Dec 2014]
3. (a) Acetic acid, CH3COOH, is made industrially by the reaction of methanol and carbon monoxide as shown by the following equation:
CH3OH(l) + CO(g) → CH3COOH(l) ΔHrxn = 355.9 kJ
Determine the amount of heat evolved when 0.5 L of acetic acid is produced.
(Given the density of CH3COOH is 1.044 g mL-1
)
(b) The molecule N2O4 is a dimer of the molecule NO2. The enthalpy of formation of
N2O4 and NO2 are +9.67 kJ mol-1 and +33.86 kJ mol-1 respectively. Calculate the standard enthalpy of reaction, in kJ mol-1 for the formation of N2O4 from NO2.
4. The combustion of one mole of ethylene (C2H2) gas to form carbon dioxide and water releases 1299.4 kJ of heat energy.
(a) Write a balanced thermochemical equation for this reaction.
(b) State whether the reaction is exothermic or endothermic.

5. Enthalpy changes for the following reactions can be determined experimentally.
4Al(s) + 3O2(g) → 2Al2O3(s) ΔH = −2332.8 kJ H2(g) +
2
1
O2(g) → H2O(g) ΔH = −420.8 kJ
Al2H6(g) + 3O2(g) → Al2O3(s) + 3H2O(g) ΔH = −2002.9 kJ
(a) Determine the molar enthalpy of formation of aluminium hydride, Al2H6 as shown below: