Topic 17. Equilibrium HL
17.1 The equilibrium law
The equilibrium law quantifies the position of equilibrium.
There are 3 ways to calculate Kc: 1) mathematical manipulation 2) ICE method 3) the ∆G equation
To solve equilibrium HL problems, use the ICE table
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I: initial concentration
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C: change concentration
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E: equilibrium concentration
Leave large answers in SCIENTIFIC NOTATION
Pearson textbook pg. 332
Calculating the equilibrium concentrations when Kc is very small
When the given Kc value is less than 10⁻³, we make the assumption that: [reactant]initial ≈ [reactant]equilibrium
Pearson textbook pg. 334
Free energy and equilibrium
∆G⁰ is the free energy change. It can be calculated for a reaction by the equation: ∆G⁰ = ∆G⁰products - ∆G⁰reactants
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(The symbol is supposed to be θ not 0, but I can't make θ a superscript)
∆G⁰ = negative → reaction proceeds in the forward direction
∆G⁰ = positive → reaction proceeds in the backward direction
∆G⁰ = 0 → reaction is at equilibrium
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at equilibrium, ∆G⁰products = ∆G⁰reactants
Kc can be calculated from thermodynamic data with the equation ∆G⁰ = - R T lnK
∆G⁰ : standard free energy change of the reaction
R : gas constant 8.31 J/K mol
T : temperature in KELVIN
lnK : natural log of Kc
Pearson textbook pg. 337
Pearson textbook pg. 337
Linking kinetics and equilibrium
rate of forward reaction = k [A] [B]
rate of backward reaction = k' [C] [D]
At equilibrium, the rate of the forward reaction = rate of the background reaction
k [A] [B] = k' [C] [D]
Therefore,
If k > k', then Kc is large -> reaction progresses towards completion
If k < k', then Kc is small -> reaction barely takes place
