Chemistry 2720 Fall 2000 Assignment 5

Due: Tuesday, Oct. 17, 9:25a.m.

1.

Industrially, methanol ( CH₃OH) is made by reaction of carbon monoxide with hydrogen. The reaction is carried out at high temperatures in the presence of a catalyst. Suppose however that you wanted to carry out the reaction at $25^\circ\mathrm{C}$, the pressures of CO and of H₂ both being held constant at 0.5bar. Is there any thermodynamic reason why this could not be done? [10 marks]

Note: Methanol boils at $65^\circ\mathrm{C}$.

2.

(a)

In a fuel cell, a fuel is fully oxidized in an isothermal reaction which occurs in aqueous solution. The oxygen is taken from the air (partial pressure of oxygen 0.2atm) so that only the fuel itself need be carried. What is the maximum electrical work which can be obtained per kilogram of the fuel hydrogen in a fuel cell operating at $25^\circ\mathrm{C}$ if a pressure regulator supplies the hydrogen at a pressure of 1atm and pure water is produced? [10 marks]

(b)

How much electrical work is produced per kilogram of hydrogen at $0^\circ\mathrm{C}$? At $-20^\circ\mathrm{C}$? Fuel cells are currently being developed for use as power sources in automobiles. Would you advise using an electrical heater to warm fuel cells installed in cars to be sold in Canada? [10 marks]

3.

The equation

$$\Delta\bar{G} = \Delta\bar{G}^\circ + RT\ln Q$$

is used to compute the Gibbs free energy of reaction under particular conditions. The enthalpy change depends extremely weakly on the reaction conditions. Use this fact to derive an equation relating the entropy change to the standard entropy change and to $\ln Q$. [10 marks]