Multiple Choice
Calculate the standard free-energy change (ΔG°) at 25 °C for the reaction: Mg(s) + Fe²⁺(aq) → Mg²⁺(aq) + Fe(s). Given: E°(Mg²⁺/Mg) = -2.37 V and E°(Fe²⁺/Fe) = -0.44 V.
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19. Chemical Thermodynamics
Gibbs Free Energy Calculations
Multiple Choice
Consider the following reaction: CO2(g) + CCl4(g) ⇌ 2COCl2(g). Calculate ΔG for this reaction at 25 °C under these conditions: PCO2 = 0.140 atm, PCCl4 = 0.185 atm, PCOCl2 = 0.755 atm. Given that ΔG°f for CO2(g) is −394.4 kJ/mol, what is the value of ΔG?
A
5.2 kJ/mol
B
0.0 kJ/mol
C
−10.5 kJ/mol
D
−5.2 kJ/mol
Verified step by step guidance1
Identify the reaction: CO2(g) + CCl4(g) ⇌ 2COCl2(g). We need to calculate the Gibbs free energy change (ΔG) for this reaction under non-standard conditions.
Use the equation ΔG = ΔG° + RT ln(Q), where ΔG° is the standard Gibbs free energy change, R is the universal gas constant (8.314 J/mol·K), T is the temperature in Kelvin, and Q is the reaction quotient.
Convert the temperature from Celsius to Kelvin: T = 25 °C + 273.15 = 298.15 K.
Calculate the reaction quotient Q using the partial pressures: Q = (P_COCl2^2) / (P_CO2 * P_CCl4). Substitute the given pressures: P_CO2 = 0.140 atm, P_CCl4 = 0.185 atm, P_COCl2 = 0.755 atm.
Calculate ΔG° for the reaction using the standard Gibbs free energy of formation: ΔG° = 2ΔG°f(COCl2) - (ΔG°f(CO2) + ΔG°f(CCl4)). Since ΔG°f for CCl4 and COCl2 are not provided, assume they are needed to find ΔG° and proceed with the calculation of ΔG using the equation from step 2.
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