W3.2_Thermodynamics

Question 1

What is thermodynamics and how are rate constants driven?

Answer 1

• ∵ Energetic changes in components of eqm
• ∴ Different eqm have different rates/Kc
• Rate constant: driven by magnitude of activation energy (Ea)

Question 2

Explain the relationship between Arrhenius equation and its Kc value.

Answer 2

• Relationship described by Arrhenius equation: k=Ae^(-Ea/(R*T))
• Ea directly relates to the rate of reaction (negatively)
• Ea in reverse reaction is different
• Kc: determined by difference in Ea between forward/reverse reaction, both passes the same stage of transition states

Question 3

Explain the relationship between ∆G and Kc with the aid of an equation. Draw an energy profile of equilbrium.

Answer 3

• Relationship between ∆G&Kc: Van’t Hoff equation ∆G=-RT(lnKc)
• ∵ Difference in energy (G) between both sides, form at different rates due to Ea difference
• ∴ Different eqm have different Kc
• Refer to the notes

Question 4

Explain what Gibb’s energy is and the characters of its equation. How does it relate to the feasibility of an equation and its Kc value?

Answer 4

• ∆G=∆H-T∆S
• ∴ Enthalpic and entropic energy contribute to magnitude of Kc
• ∆H: heat-related, bonding environment changes energy level (-ve: exo/+ve: endo)
• T: temperature (K)
• ∆S: level of disorder
• ∵ Reactions are only feasible when ∆G≼0
• +ve ∆H, +ve ∆S: Feasible at high temperature
• -ve ∆H, +ve ∆S: Always feasible
• +ve ∆H, -ve ∆S: Never feasible
• -ve ∆H, -ve ∆S: Feasible at low temperature
• All equations above have a temperature constant (T) -> temperature affects Kc

Question 5

Explain what would happen when an equilibrium equation is mediated by enzymes (biological/protein catalysts) in biological processes.

Answer 5

• Ea reduced -> rate of forward and backward reactions increased (refer to Arrhenius equation)
• ∆G remains unchanged -> Kc does not change (refer to Van’t Hoff equation)