Calculate Δg for The Following Reaction at 298 K Chegg

The Gibbs free energy change (ΔG) is a fundamental concept in thermodynamics that helps predict whether a chemical reaction will occur spontaneously. At 298 K (25°C), this calculation is particularly useful for standard conditions in many chemical and biochemical processes.

What is ΔG?

ΔG represents the change in Gibbs free energy for a chemical reaction. It combines enthalpy (ΔH) and entropy (ΔS) to determine the spontaneity of a process. A negative ΔG indicates a spontaneous reaction, while a positive ΔG means the reaction is non-spontaneous as written.

Gibbs free energy accounts for both energy changes and disorder in a system, making it essential for predicting reaction feasibility.

Gibbs Free Energy Formula

ΔG = ΔH - TΔS

Where:

ΔG = Change in Gibbs free energy (kJ/mol)
ΔH = Change in enthalpy (kJ/mol)
T = Temperature in Kelvin (K)
ΔS = Change in entropy (kJ/mol·K)

At 298 K (25°C), the temperature is a constant value in the equation, so it's often included as part of the entropy term.

How to Calculate ΔG

Determine the change in enthalpy (ΔH) for the reaction.
Calculate the change in entropy (ΔS) for the reaction.
Multiply the temperature (298 K) by ΔS to get TΔS.
Subtract TΔS from ΔH to find ΔG.

For standard conditions, you can use standard enthalpy and entropy values from thermodynamic tables.

Worked Example

Consider the reaction: 2H₂(g) + O₂(g) → 2H₂O(g)

Given:

ΔH = -483.6 kJ/mol
ΔS = -10.1 kJ/mol·K

Calculation:

ΔG = ΔH - TΔS

ΔG = (-483.6) - (298 × -10.1)

ΔG = -483.6 - (-2999.8)

ΔG = -483.6 + 2999.8

ΔG = 2516.2 kJ/mol

This positive ΔG indicates the reaction is non-spontaneous under standard conditions.

Interpreting Results

ΔG Value	Interpretation
ΔG < 0	Spontaneous reaction
ΔG = 0	Reaction at equilibrium
ΔG > 0	Non-spontaneous reaction

Understanding ΔG helps chemists design reactions, predict product formation, and optimize industrial processes.

FAQ

What units are used for ΔG?: ΔG is typically measured in kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).
Can ΔG be negative?: Yes, a negative ΔG indicates a spontaneous reaction that releases free energy.
How does temperature affect ΔG?: The temperature term (TΔS) becomes more significant at higher temperatures, potentially changing the spontaneity of reactions.
What if I don't know ΔH and ΔS?: You can look up standard thermodynamic values for common reactions or use experimental data.
Is ΔG the same as free energy?: Yes, ΔG represents the change in free energy available to do work in a system.