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In a reaction, if the enthalpy change (ΔH) is -100 kJ and the entropy change (ΔS

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Question: In a reaction, if the enthalpy change (ΔH) is -100 kJ and the entropy change (ΔS) is 200 J/K, what is the Gibbs free energy change (ΔG) at 298 K?

Options:

  1. -100 kJ
  2. -50 kJ
  3. 0 kJ
  4. 50 kJ

Correct Answer: -100 kJ

Solution: 

ΔG = ΔH - TΔS = -100 kJ - (298 K * 0.2 kJ/K) = -100 kJ - 59.6 kJ = -159.6 kJ.

In a reaction, if the enthalpy change (ΔH) is -100 kJ and the entropy change (ΔS

Practice Questions

Q1
In a reaction, if the enthalpy change (ΔH) is -100 kJ and the entropy change (ΔS) is 200 J/K, what is the Gibbs free energy change (ΔG) at 298 K?
  1. -100 kJ
  2. -50 kJ
  3. 0 kJ
  4. 50 kJ

Questions & Step-by-Step Solutions

In a reaction, if the enthalpy change (ΔH) is -100 kJ and the entropy change (ΔS) is 200 J/K, what is the Gibbs free energy change (ΔG) at 298 K?
  • Step 1: Identify the values given in the problem. We have ΔH = -100 kJ and ΔS = 200 J/K.
  • Step 2: Convert ΔS from J/K to kJ/K because ΔH is in kJ. Since 1 kJ = 1000 J, we convert 200 J/K to kJ/K: 200 J/K = 0.2 kJ/K.
  • Step 3: Identify the temperature (T) given in the problem, which is 298 K.
  • Step 4: Use the Gibbs free energy formula: ΔG = ΔH - TΔS.
  • Step 5: Substitute the values into the formula: ΔG = -100 kJ - (298 K * 0.2 kJ/K).
  • Step 6: Calculate TΔS: 298 K * 0.2 kJ/K = 59.6 kJ.
  • Step 7: Substitute this value back into the equation: ΔG = -100 kJ - 59.6 kJ.
  • Step 8: Perform the final calculation: ΔG = -100 kJ - 59.6 kJ = -159.6 kJ.
  • Gibbs Free Energy – The Gibbs free energy change (ΔG) is calculated using the formula ΔG = ΔH - TΔS, where ΔH is the enthalpy change, T is the temperature in Kelvin, and ΔS is the entropy change.
  • Units Conversion – Understanding the need to convert units, specifically converting ΔS from J/K to kJ/K to match the units of ΔH.
  • Thermodynamic Principles – Application of thermodynamic principles to determine spontaneity of a reaction based on ΔG.
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