The value of Ka for nitrous acid (HNO2) at 25^∘ C is given in Appendix D. (a) Write the chemical

step 1 Straightaway jumping to the answers. So starting with option A, we have nitrous acid, that is HN

The value of Ka for nitrous acid (HNO2) at 25^∘ C is given...

The value of $K_{a}$ for nitrous acid $\left(\mathrm{HNO}_{2}\right)$ at $25^{\circ} \mathrm{C}$ is given in Appendix D. (a) Write the chemical equation for the equilibrium that corresponds to $K_{a}$. (b) By using the value of $K_{a}$, calculate $\Delta G^{\circ}$ for the dissociation of nitrous acid in aqueous solution. (c) What is the value of $\Delta G$ at equilibrium? (d) What is the value of $\Delta G$ when $\left[\mathrm{H}^{+}\right]=5.0 \times 10^{-2} \mathrm{M}$ $\left[\mathrm{NO}_{2}^{-}\right]=6.0 \times 10^{-4} \mathrm{M},$ and $\left[\mathrm{HNO}_{2}\right]=0.20 \mathrm{M} ?$

The value of $K_{a}$ for nitrous acid $\left(\mathrm{HNO}_{2}\right)$ at $25^{\circ} \mathrm{C}$ is given in Appendix D.
(a) Write the chemical equation for the equilibrium that corresponds to $K_{a}$. (b) By using the value of $K_{a}$, calculate $\Delta G^{\circ}$ for the dissociation of nitrous acid in aqueous solution. (c) What is the value of $\Delta G$ at equilibrium? (d) What is the value of $\Delta G$ when $\left[\mathrm{H}^{+}\right]=5.0 \times 10^{-2} \mathrm{M}$ $\left[\mathrm{NO}_{2}^{-}\right]=6.0 \times 10^{-4} \mathrm{M},$ and $\left[\mathrm{HNO}_{2}\right]=0.20 \mathrm{M} ?$

Key Concepts

Reaction Quotient (Q) and Gibbs Free Energy (?G)

The reaction quotient, Q, is calculated using the concentrations of reactants and products at any point during a reaction. The Gibbs free energy change, ?G, under non-standard conditions can be determined using the equation ?G = ?G° + RT ln Q. This expression allows one to assess the spontaneity of a reaction at any moment by comparing Q to the equilibrium constant, revealing how deviations from equilibrium affect the free energy.

Standard Gibbs Free Energy Change (?G°)

The standard Gibbs free energy change, ?G°, is the change in free energy when a reaction occurs under standard conditions. It is related to the equilibrium constant through the equation ?G° = -RT ln K, where R is the gas constant and T is the temperature in Kelvin. This relationship bridges the concept of thermodynamics with chemical equilibrium, indicating whether a reaction is spontaneous under standard conditions.

Chemical Equilibrium

Chemical equilibrium refers to the state of a reversible reaction where the rate of the forward reaction equals the rate of the reverse reaction, leading to constant concentrations of all reactants and products. This concept is fundamental in understanding how reactions establish a balance and how changes in conditions can shift this balance according to Le Chatelier's Principle.

Acid Dissociation Constant (Ka)

The acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is defined as the equilibrium constant for the dissociation of an acid into its conjugate base and a proton. It provides insight into the extent of ionization and is directly related to the pH of the solution.

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