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Multiple Choice
Calculate the value of ΔG° at 281.0 °C for the formation of calcium chloride from its constituent elements: Ca(s) + Cl2(g) → CaCl2(s), given that at 25.0 °C, ΔH° is -795.8 kJ/mol and ΔG° is -748.1 kJ/mol.
A
-750.0 kJ/mol
B
-740.0 kJ/mol
C
-760.0 kJ/mol
D
-748.1 kJ/mol
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Verified step by step guidance
1
Understand that ΔG° can be calculated using the Gibbs free energy equation: ΔG° = ΔH° - TΔS°, where T is the temperature in Kelvin and ΔS° is the change in entropy.
Convert the given temperature from Celsius to Kelvin by adding 273.15 to the Celsius temperature: T(K) = 281.0 + 273.15.
Recognize that the change in entropy (ΔS°) can be estimated using the relationship between ΔG° and ΔH° at the reference temperature (25.0 °C or 298.15 K): ΔG° = ΔH° - TΔS°. Rearrange to find ΔS°: ΔS° = (ΔH° - ΔG°) / T.
Calculate ΔS° using the values at 25.0 °C: ΔS° = (-795.8 kJ/mol - (-748.1 kJ/mol)) / 298.15 K.
Use the calculated ΔS° and the converted temperature in Kelvin to find ΔG° at 281.0 °C: ΔG° = ΔH° - TΔS°, substituting the values for ΔH°, T, and ΔS°.