Multiple Choice
Consider the following reaction: I2(g) + Cl2(g) ⇌ 2ICl(g) with Kp = 81.9 at 25 °C. Calculate ΔG⁰rxn for the reaction at 25 °C under equilibrium conditions. Express your answer in kilojoules.
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19. Chemical Thermodynamics
Gibbs Free Energy Calculations
Multiple Choice
Consider the oxidation of NO to NO2: NO(g) + 1/2 O2(g) → NO2(g). Calculate ΔG°rxn at 25 °C given the following standard Gibbs free energies of formation: ΔG°f(NO) = 86.6 kJ/mol, ΔG°f(O2) = 0 kJ/mol, ΔG°f(NO2) = 51.3 kJ/mol.
A
35.3 kJ/mol
B
137.9 kJ/mol
C
-137.9 kJ/mol
D
-35.3 kJ/mol
Verified step by step guidance1
Understand that the Gibbs free energy change for a reaction, ΔG°rxn, can be calculated using the standard Gibbs free energies of formation (ΔG°f) of the reactants and products. The formula is: ΔG°rxn = ΣΔG°f(products) - ΣΔG°f(reactants).
Identify the reactants and products in the given chemical equation: NO(g) and O2(g) are the reactants, and NO2(g) is the product.
Write the expression for ΔG°rxn using the given values: ΔG°rxn = ΔG°f(NO2) - [ΔG°f(NO) + 1/2 * ΔG°f(O2)].
Substitute the given standard Gibbs free energies of formation into the expression: ΔG°rxn = 51.3 kJ/mol - [86.6 kJ/mol + 1/2 * 0 kJ/mol].
Perform the arithmetic operations to find ΔG°rxn. Remember that the Gibbs free energy of formation for O2 is zero, so it does not contribute to the calculation.
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