In Part A, we saw that G =242.1 kJ for the hydrogenation of acetylene under stan
ID: 961394 • Letter: I
Question
In Part A, we saw that G=242.1 kJ for the hydrogenation of acetylene under standard conditions (all pressures equal to 1 atm and the common reference temperature 298 K). In Part B, you will determine the G for the reaction under a given set of nonstandard conditions.
Part B
At 25 C the reaction from Part A has a composition as shown in the table below.
What is the free energy change, G, in kilojoules for the reaction under these conditions?
Substance Pressure(atm) C2H2(g) 3.95 H2(g) 5.65 C2H6(g) 5.25×102
Explanation / Answer
The reaction:
C2H2(g) + 2H2(g) = C2H6(g)
Information:
1) Calculate Kp using the formula:
Kp = (P products) / (P reagents)
Use the balanced chemical equation and transform the equation into:
Kp = (P C2H6) / (P H2)2(P C2H2)
Note: the superscript 2 in H2 is there because in the balanced chemical equation, the coefficient of H2 is 2.
Substitute the values:
Kp = (0.0525 atm) / (5.65 atm)2(3.95 atm)
Kp = 0.0004163 atm-2
Calculate G using the formula:
G = -RTlnKp
Substitute the values:
G = -(8.314 J/molK)(298K)ln(0.0004163)
G = 19285.34 J/mol
G = 19.3 kJ/mol (3 significant figures)
Answer: the reaction's G is 19.3 kJ/mol.
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