Question 1

How does the equilibrium constant relate to standard free energy change?

Accepted Answer

The standard free energy change equals negative RT times the natural logarithm of the equilibrium constant. When ΔG° is negative, the equilibrium constant is greater than 1, favoring product formation. Conversely, when ΔG° is positive, K is less than 1, favoring reactants. This relationship allows you to predict reaction favorability from either thermodynamic property.

Question 2

What does a negative free energy change indicate about a reaction?

Accepted Answer

A negative ΔG represents a driving force for the process in the forward direction, indicating the reaction is spontaneous and product-favored at equilibrium. The more negative the free energy, the larger the equilibrium constant and the greater the tendency for reactants to convert to products. This thermodynamic property predicts whether a reaction will proceed spontaneously under given conditions.

Question 3

How does temperature affect the equilibrium constant?

Accepted Answer

Temperature changes alter the equilibrium constant according to the relationship ln K equals negative ΔH over RT plus ΔS over R. Plotting the natural log of K against inverse temperature yields a straight line with slope negative ΔH over R and y-intercept ΔS over R. This temperature dependence allows calculation of enthalpy changes from equilibrium data measured at two different temperatures.

Question 4

What is the relationship between the reaction quotient and equilibrium?

Accepted Answer

The reaction quotient Q measures the current ratio of products to reactants. When Q is less than the equilibrium constant K, the reaction proceeds forward until equilibrium is reached and Q equals K. When Q exceeds K, the reaction shifts in reverse. At equilibrium, Q equals K and the free energy change is zero, meaning forward and reverse driving forces are equal.

Question 5

How is free energy change calculated for nonstandard conditions?

Accepted Answer

The free energy change under nonstandard conditions is calculated as ΔG equals ΔG° plus RT times the natural log of Q, where Q is the reaction quotient. This equation applies to reactants and products at pressures other than 1 bar or concentrations other than 1 M. It allows prediction of reaction spontaneity under any given set of conditions by comparing actual conditions to standard states.

Question 6

What does it mean when ΔG° equals zero at equilibrium?

Accepted Answer

When ΔG° equals zero, the system is at equilibrium with reactants and products comparably abundant. The equilibrium constant K equals 1, and the forward and reverse reaction rates are equal. At this point, the reaction quotient Q equals the equilibrium constant, and there is no net driving force for the reaction to proceed in either direction.

Question 7

Why is the Van't Hoff equation useful for analyzing equilibrium data?

Accepted Answer

The Van't Hoff equation, expressed as ln K equals negative ΔH over RT plus ΔS over R, creates a linear relationship between ln K and inverse temperature. This straight-line form enables graphical determination of enthalpy and entropy changes from experimental equilibrium constants measured at different temperatures, assuming enthalpy remains constant over the limited temperature range studied.

Свободная энергия и равновесие

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