Edexcel A-Level Chemistry 9CH0
Atomic Structure and the Periodic Table
Bonding and Structure
Inorganic Chemistry and the Periodic Table
Formulae, Equations and Amounts of Substance
Organic Chemistry I
Modern Analytical Techniques I
Energetics I
Kinetics I
Equilibrium I
Acid-Base Equilibria
Energetics II
Redox II
Transition Metals
Kinetics II
Organic Chemistry II
Organic Chemistry III
Energetics II
Gibbs free energy and thermodynamic feasibility
- 3 things to know
- Papers 1 and 3
Overview
Recall questions on the Gibbs equation, on what makes a reaction feasible, on finding the temperature at which it becomes so, and on why a feasible reaction may still be slow.
What you need to know
Answer each one before you reveal it.
State the equation for Gibbs free energy change.
What two factors together determine whether a reaction is thermodynamically feasible?
Questions from this subtopic
Each one with the model answer underneath.
- 1
What two factors together determine whether a reaction is thermodynamically feasible?
Model answer
Whether the enthalpy term or the entropy term wins out.
- 2
State the equation for Gibbs free energy change.
Model answer
ΔG = ΔH − TΔS_system
- 3
In the Gibbs free energy equation, what does T represent?
Model answer
The absolute temperature in kelvin.
- 4
Calculate the Gibbs free energy change when enthalpy change = 421 kJ mol⁻¹, temperature = 209 K, entropy change of system = 196 J K⁻¹ mol⁻¹.
Model answer
Gibbs free energy change = 421 - (209 × 196 ÷ 1000) = 380 kJ mol⁻¹.
- 5
What condition for Gibbs free energy indicates that a reaction is thermodynamically feasible?
Model answer
The Gibbs free energy change must be negative (ΔG < 0).
- 6
Given ΔH and ΔS, how do you find the temperature above which a reaction becomes feasible?
Model answer
By setting ΔG = 0 and rearranging to give T = ΔH / ΔS_system.
Other ways to work this
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