Question

Item 5

The equilibrium constant of a system, K, can be related to the standard free energy change, ΔG, using the following equation:

ΔG∘=−RTlnK

where T is standard temperature in kelvins and R is the gas constant.

Under conditions other than standard state, the following equation applies:

ΔG=ΔG∘+RTlnQ

In this equation, Q is the reaction quotient and is defined the same manner as K except that the concentrations or pressures used are not necessarily the equilibrium values.

Part A

Acetylene, C2H2, can be converted to ethane, C2H6, by a process known as hydrogenation. The reaction is C2H2(g)+2H2(g)⇌C2H6(g)Use tabulated values of ΔfGo to calculate  ΔrGo ,and obtain the value of  Keq   for this reaction.

Express your answer using two significant figures.

Hints

Keq =

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Standard versus Nonstandard Conditions

In Part A, we calculatedΔG∘ for the hydrogenation of acetylene under standard conditions. In Part B, you will determine the ΔG 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.

Substance	Pressure ( bar)
C2H2(g)	4.85
H2(g)	5.15
C2H6(g)	4.25×10−2

What is the free energy change, ΔG, in kilojoules for the reaction under these conditions?

Express your answer numerically in kilojoules.

Hints

ΔG =

kJ

Answer 1