Worksheet: Gibbs Free Energy

In this worksheet, we will practice calculating changes in molar Gibbs free energy from standard molar entropy and enthalpy change data.

Q1:

Ethane gas can be produced by the hydrogenation of gaseous ethene. The standard entropies and enthalpies of formation for ethene and other materials are shown in the table.

Material Standard Molar Entropy 𝑆 ( J / K · m o l ) Standard Enthalpy of Formation Δ 𝐻 ( k J / m o l )
C 2 H 2 ( g ) 200.9 227.4
C 2 H 4 ( g ) 219.3 52.4
C 2 H 6 ( g ) 229.2 8 4 . 0
H ( g ) 114.7 218.0
H 2 ( g ) 130.7 0

The standard change in Gibbs free energy, Δ 𝐺 , for the hydrogenation of ethene at 298 K is expressed per mole of ethene reacted. Calculate, to 3 significant figures, the value of Δ 𝐺 at 298 K.

Q2:

Consider the reaction and the table of free energies of formation below:

Substance B C l ( ) 3 g H O ( ) 2 l B ( O H ) ( ) 3 s H C l ( ) g
Δ 𝐺 f ( k i l o j o u l e s p e r m o l e ) 3 8 8 . 7 2 3 7 . 1 9 6 8 . 9 2 9 5 . 2 9 9

What is the standard free energy change for the reaction?

Q3:

Consider the reaction and the table of free energies of formation below:

Substance B F ( ) 3 g H O ( ) 2 l B ( O H ) ( ) 3 s H F ( ) g
Δ 𝐺 f ( k J / m o l ) 1 1 1 9 . 4 2 3 7 . 1 9 6 8 . 9 2 2 7 5 . 4

What is the standard free energy change for the reaction?

Q4:

Consider the reaction and the table of free energies of formation below:

Substance B H ( ) 2 6 g H O ( ) 2 l B ( O H ) ( ) 3 s H ( ) 2 g
Δ 𝐺 f ( k J / m o l ) 87.6 2 3 7 . 1 9 6 8 . 9 2 0

What is the standard free energy change for the reaction, to the nearest kJ/mol?

Q5:

Consider the reaction C u ( ) + 4 N H ( ) C u ( N H ) ( ) 2 + 3 3 4 2 + a q a q a q , for which Δ 𝐺 = 7 0 . 5 4 r k J at 298 K. If the activities of C u 2 + , N H 3 and C u ( N H ) 3 4 2 + in a reaction mixture at 298 K are all equal to 0.01, what is the value of Δ 𝐺 r ?

Q6:

Fill in the blank to complete the following analogy. Thermodynamics is to free energy as kinetics is to .

  • AElectron transfer
  • BThermal energy
  • CEntropy
  • DActivation energy
  • EEnthalpy

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