Following reaction occurs at 25^∘ C 2 NO(g, 1 ×10^-5 atm)+Cl2( g, 1 ×10^-2 arm) ⇌2 NOCl(g, 1 ×1

step 1 Given reaction in the question is 2NO, 2NO, which is in gaseous form and the partial pressure is

Following reaction occurs at 25^∘ C 2 NO(g, 1 ×10^-5...

Following reaction occurs at $25^{\circ} \mathrm{C}$ $2 \mathrm{NO}\left(\mathrm{g}, 1 \times 10^{-5} \mathrm{~atm}\right)+\mathrm{Cl}_2\left(\mathrm{~g}, 1 \times 10^{-2} \mathrm{arm}\right) \rightleftharpoons$ $2 \mathrm{NOCl}\left(\mathrm{g}, 1 \times 10^{-2} \mathrm{~atm}\right) \Delta \mathrm{G}^{\circ}$ is (a) -45.65 kJ (b) -66.53 kJ (c) -22.82 kJ (d) -35.65 kJ

Following reaction occurs at $25^{\circ} \mathrm{C}$ $2 \mathrm{NO}\left(\mathrm{g}, 1 \times 10^{-5} \mathrm{~atm}\right)+\mathrm{Cl}_2\left(\mathrm{~g}, 1 \times 10^{-2} \mathrm{arm}\right) \rightleftharpoons$ $2 \mathrm{NOCl}\left(\mathrm{g}, 1 \times 10^{-2} \mathrm{~atm}\right) \Delta \mathrm{G}^{\circ}$ is
(a) -45.65 kJ
(b) -66.53 kJ
(c) -22.82 kJ
(d) -35.65 kJ

Key Concepts

Standard Gibbs Free Energy Change (?G°)

This concept refers to the change in Gibbs free energy when a reaction occurs under standard conditions (usually 1 atm for gases, 1 M for solutes, and a specified temperature, typically 25°C). ?G° indicates the thermodynamic favorability of a reaction under these defined conditions and is a critical parameter in determining whether a reaction is spontaneous or requires input of energy.

Equilibrium Constant (K) and Reaction Quotient (Q)

The equilibrium constant (K) is a dimensionless value that expresses the ratio of the concentrations (or activities, which for gases can be represented by partial pressures) of products to reactants at equilibrium, each raised to the power of their stoichiometric coefficients. The reaction quotient (Q) is calculated similarly but for a system that is not necessarily at equilibrium. Both K and Q provide insight into the position of equilibrium and the direction in which a reaction will proceed to reach equilibrium.

Relationship Between ?G° and Equilibrium Constant

There is a fundamental relationship between the standard Gibbs free energy change and the equilibrium constant, given by the equation ?G° = -RT lnK. This equation connects the thermodynamic favorability of a reaction (through ?G°) with its equilibrium position (through K), where R is the universal gas constant and T is the temperature in Kelvin. It allows one to predict the extent to which a reaction will proceed under standard conditions.

Partial Pressures as a Measure of Activity for Gases

In the context of gaseous reactions, partial pressures are used as a practical measure for the activities of the gases involved. Under ideal conditions, the activity of a gas is proportional to its partial pressure divided by a standard pressure (usually 1 atm). This concept simplifies the calculations of equilibrium constants and Gibbs free energy changes for reactions involving gases, as it allows the use of measurable quantities like pressure in thermodynamic equations.

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