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Chemistry · University

Gibbs energy with consistent units

Convert entropy to the same energy unit as enthalpy. Temperature is in kelvin.

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Method and conditions

Convert entropy to the same energy unit as enthalpy. Temperature is in kelvin.

ΔG = ΔH − TΔS

Worked examples

For a model reaction, ΔH=5 kJ/mol, ΔS=-9 J/(mol·K), and T=430 K. Find ΔG in kJ/mol. Round the final result to 4 decimal places if needed. Answer in kJ/mol.

ΔS=-0.009 kJ/(mol·K). Use ΔG=5−430(-0.009).

8.87 kJ/mol

For a model reaction, ΔH=-88 kJ/mol, ΔS=88 J/(mol·K), and T=360 K. Find ΔG in kJ/mol. Round the final result to 4 decimal places if needed. Answer in kJ/mol.

ΔS=0.088 kJ/(mol·K). Use ΔG=-88−360(0.088).

-119.68 kJ/mol

Try it

  1. For a model reaction, ΔH=94 kJ/mol, ΔS=-155 J/(mol·K), and T=340 K. Find ΔG in kJ/mol. Round the final result to 4 decimal places if needed. Answer in kJ/mol.

  2. For a model reaction, ΔH=26 kJ/mol, ΔS=-94 J/(mol·K), and T=320 K. Find ΔG in kJ/mol. Round the final result to 4 decimal places if needed. Answer in kJ/mol.

Check your work

Answers and marking notes
  1. 146.7 kJ/mol

    ΔS=-0.155 kJ/(mol·K). Use ΔG=94−340(-0.155).

  2. 56.08 kJ/mol

    ΔS=-0.094 kJ/(mol·K). Use ΔG=26−320(-0.094).

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