91Ó°ÊÓ

The heat capacity of air at room temperature \(\left(20^{\circ} \mathrm{C}\right)\) is approximately \(21 \mathrm{JK}^{-1} \mathrm{mol}^{-1}\). (Section 13.1 ) (a) How much heat is required to raise the temporature of a \(5 m \times 5 m \times 3 m\) room by \(10^{\circ} \mathrm{C} ?\) (b) How long will it take a \(1 \mathrm{kW}\) heater to achieve this? (Assume that the volume of 1 mol of air is \(24 \mathrm{dm}^{3}\) at \(20^{\circ} \mathrm{C} .\)

Calculate the onthalpy change when \(100 \mathrm{g}\) of water froezes at \(0^{\circ} \mathrm{C}\). (The standard enthalpy change of fusion of water is \(+6.01 \mathrm{kJmol}^{-1}\), ) (Section 13.2)

Calcite and aragonite are two forms of calcium carbonate. Calculate the enthalpy change for the transition from calcite to aragonite. (AH(calcite) \(=-1206.9 \mathrm{kJ} \mathrm{mol}^{-1}\) and \(\Delta \mathrm{H}\) (aragonite) \(=\) \(-1207.1 \mathrm{kJ} \mathrm{mol}^{-1}\), j (Section 13.3)

A chemist is trying to measure the enthalpy change for the hydration reaction: \\[ \mathrm{Na}_{2} \mathrm{CO}_{3}(\mathrm{s}) \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}(\mathrm{s}) \\] Calibration of a solution calorimeter shows that 357.9 J of heat raises the temperature by \(1.00 \mathrm{K}\). When \(2.500 \mathrm{g}\) of anhydrous sodium carbonate, \(\mathrm{Na}_{2} \mathrm{CO}_{3}\), was dissolved in \(100.00 \mathrm{cm}^{3}\) of water, the temperature increased by \(1.550 \mathrm{K}\). On dissolving \(3.500 \mathrm{g}\) of sodium carbonate decahydrate, \(\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}\) in \(100.00 \mathrm{cm}^{3}\) of water, the temperature decreased by \(2.310 \mathrm{K}\) Calculate enthalpy change of hydration of sodium carbonate. (Section 13.5 )