What is the relationship between the free-energy change under nonstandard-state conditions, ∆G, the free-energy change under standard-state conditions, ∆G°, and the reaction quotient, Q?
Verified step by step guidance
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Step 1: Understand the concept of free energy change (∆G) in a chemical reaction, which indicates the spontaneity of the reaction. A negative ∆G means the reaction is spontaneous, while a positive ∆G means it is non-spontaneous.
Step 2: Recognize that ∆G° is the free energy change under standard-state conditions, which are typically 1 atm pressure for gases, 1 M concentration for solutions, and pure solids or liquids for other phases at a specified temperature (usually 298 K).
Step 3: Learn about the reaction quotient, Q, which is a measure of the relative amounts of products and reactants present during a reaction at a given point in time. It is calculated using the same expression as the equilibrium constant, K, but for non-equilibrium conditions.
Step 4: Use the relationship between ∆G, ∆G°, and Q, which is given by the equation: ∆G = ∆G° + RT ln(Q), where R is the universal gas constant (8.314 J/mol·K) and T is the temperature in Kelvin.
Step 5: Analyze how this equation shows that the free energy change under nonstandard conditions (∆G) depends on both the standard free energy change (∆G°) and the reaction quotient (Q). When Q = 1, ∆G = ∆G°. When Q < K, ∆G is negative, indicating the reaction will proceed forward. When Q > K, ∆G is positive, indicating the reaction will proceed in reverse.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Gibbs Free Energy
Gibbs free energy (G) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. The change in Gibbs free energy (∆G) indicates the spontaneity of a reaction; a negative ∆G suggests that a reaction can occur spontaneously, while a positive ∆G indicates non-spontaneity.
The standard free energy change (∆G°) refers to the change in Gibbs free energy when a reaction occurs under standard conditions, typically defined as 1 bar pressure and 1 M concentration for all reactants and products. It provides a reference point for predicting the direction of a reaction and is crucial for understanding how actual conditions deviate from these standards.
The reaction quotient (Q) is a dimensionless number that reflects the ratio of the concentrations of products to reactants at any point in a reaction, not necessarily at equilibrium. It is used to determine the direction in which a reaction will proceed to reach equilibrium, as it compares the current state of the reaction to the equilibrium state defined by the equilibrium constant (K).
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