Chapter 21, Chemical reactions Video Solutions, Thermodynamics: A complete undergraduate course

Problem 1

A reaction $A+B \rightarrow C+D$ is exothermic and produces a positive entropy change. Is such a reaction (i) possible at high temperature, (ii) possible only at low temperature, (iii) not possible at any temperature, or (iv) possible at any temperature?

Ajay Singhal

Numerade Educator

03:10

Problem 2

By what factor does the reaction rate given by equation (21.7) increase when the temperature changes from $300 \mathrm{~K}$ to $310 \mathrm{~K}$, for a reaction whose activation energy is $0.5 \mathrm{eV}$ ?

Crystal Wang

Numerade Educator

03:27

Problem 3

Show that the law of mass action applied to the process of ionization of hydrogen reads
$$
\frac{n_e n_{\mathrm{p}}}{n_{\mathrm{H}}}=n^{\ominus} e^{-\Delta \mu^{\ominus} / k_{\mathrm{B}} T} \text {, }
$$
where $\Delta \mu^{\ominus}=\mu_{\mathrm{p}}^{\ominus}+\mu_{\mathrm{e}}^{\ominus}-\mu_{\mathrm{H}}^{\ominus}$ and $n^{\ominus}$ is the standard density introduced in equation (21.11). Obtain this combination by using equation (12.8) for a gas at the standard density $n^{\ominus}$, and allowing for the binding energy. Hence obtain the Saha equation.

Khoobchandra Agrawal

Numerade Educator

01:35

Problem 4

The equilibrium constant for the gaseous reaction
$$
\mathrm{H}_2+\mathrm{I}_2 \leftrightharpoons 2 \mathrm{HI}
$$
at a temperature of 720 kelvin is $K=46.8$. A flask initially containing only $\mathrm{HI}$ is prepared and maintained at 720 kelvin. What is the concentration of $\mathrm{HI}$ in the flask when chemical equilibrium is attained? [Ans. $77 \%$ by volume]

Anthony Han

Numerade Educator

06:01

Problem 5

An important step in the commercial production of sulphuric acid involves synthesis of sulphur trioxide, in the reaction
$$
2 \mathrm{SO}_2+\mathrm{O}_2 \leftrightharpoons 2 \mathrm{SO}_3
$$
At $298 \mathrm{kelvin}$, one finds $\Delta H=-1.9824 \times 10^5 \mathrm{~J}$ and $\Delta S=-189.79 \mathrm{~J} / \mathrm{K}$ per mole of oxygen molecules in this reaction. Assuming these values are independent of temperature, find the reaction quotient at $T=300 \mathrm{~K}$ and at $T=1200 \mathrm{~K}$. Hence establish whether the reaction favours production or dissociation of $\mathrm{SO}_3$ at these two temperatures.

Henry He

Numerade Educator

Problem 6

Prove (21.26), for example by substituting from (21.27) and (21.25).

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