Equilibrium constants Kc and Kp – ICE tables
ChemistryKinetics & EquilibriumAges 16–17
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Sign in to playEnter starting amounts for several runs, watch the system reach equilibrium on a concentration–time graph while the ICE table fills in, and see that Kc comes out the same every time at a fixed temperature. Calculate Kp from mole fractions and partial pressures, predict the direction of reaction by comparing Q with K, practise ICE-table problems that are marked, and explore how K changes when a reaction is reversed, multiplied or added, together with ΔG° = −RT ln K.
Lesson: Equilibrium constants Kc and Kp – ICE tables, the reaction quotient Q and the effect of temperature on K
What it shows
At equilibrium the forward and reverse reactions run at the same rate, so concentrations stop changing. The equilibrium constant Kc = [products]^coefficients / [reactants]^coefficients has the same value whatever the starting amounts, as long as the temperature is fixed. For gases, Kp uses partial pressures (mole fraction × total pressure), and Kp = Kc(RT)^Δn. Comparing the reaction quotient Q with K tells you which way a mixture will react. Only temperature changes K: raising T lowers K for an exothermic reaction and raises it for an endothermic one.
How to use
On the Experiments tab choose the System, set Temperature and Volume, type the starting amounts and press Run to equilibrium (or Jump to equilibrium). Each run is added to the results table, so compare Kc across runs. Choose a Pressure unit for Kp to see mole fractions and partial pressures. On the ICE problems tab press New problem, enter your answer and press Check, or use Next step. On the Manipulating K tab reverse, multiply or add reactions and move the size-of-K slider.
Parameters you can change
- Screen Experiments: runs to equilibrium, ICE-table problems, Manipulating K and the size of K
- Equilibrium system H₂ + I₂ ⇌ 2HI, N₂O₄ ⇌ 2NO₂, N₂ + 3H₂ ⇌ 2NH₃, Esterification: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
- Temperature (limited to each system's range) 0–600 °C
- Volume of the vessel 0.5–20 L
- Starting amount of the first reactant 0–10 mol
- Starting amount of the second reactant 0–10 mol
- Starting amount of the first product 0–10 mol
- Starting amount of the second product 0–10 mol
- Pressure unit for Kp bar, atm, kPa
- Starting log K on the Manipulating K screen -10–10
Questions to explore
- Does Kc change when you start with twice as much hydrogen? Why or why not?
- If Q is greater than K, in which direction does the reaction go to reach equilibrium?
- Why does raising the temperature increase K for N₂O₄ ⇌ 2NO₂ but decrease it for ammonia synthesis?
