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CHEMISTRY • EQUILIBRIUM
Chemical Equilibrium
Compare the reaction quotient Q with K, separate the current mixture from the equilibrium composition, and design an equilibrium constant for a requested product fraction.
● LIVE EQUILIBRIUM STATEK versus Q
Species BSpecies AReference K
K—
Q—
Equilibrium B—
Predicted shift—
Reference B—
Target error—
Do not confuse Q with K
K defines the equilibrium composition for this simplified A ⇌ B system; Q describes the current mixture. Their comparison predicts which direction the composition must change to approach equilibrium.
Fast investigations
- Hold K = 1 and move the current B fraction across 0.5.
- Increase K by powers of ten and track the equilibrium B fraction.
- Compare two K values at the same total concentration.
- Use the challenge to derive the K needed for 80% B at equilibrium.
LEARN WITH THE SIMULATION
Understand Chemical Equilibrium by experimenting.
START HERE
Chemical equilibrium is dynamic: forward and reverse reactions continue while macroscopic composition remains stable. Comparing the reaction quotient Q with the equilibrium constant K predicts which direction the system must shift.
BUILD THE IDEA
What you should understand first
- Distinguish Q from K.
- Predict shift direction from Q < K or Q > K.
- Connect equilibrium composition to the value of K in a simple A ⇌ B model.
TRY IT YOURSELF
How does increasing K change the equilibrium fraction of product B?
- Start with K near 1 and note the equilibrium composition.
- Increase K by orders of magnitude.
- Compare the predicted product fraction and shift tendency from the same starting mixture.
Read the visual:
Larger K favors product at equilibrium in this simple 1:1 model.
WHY IT WORKS 01
Distinguish Q from K.
Chemical equilibrium is dynamic rather than static. Reactant and product molecules continue to react in both directions, but the forward and reverse rates become equal, so concentrations stop changing macroscopically. The equilibrium constant K describes the ratio favored at a given temperature; it does not mean equal concentrations and it does not tell how quickly equilibrium is reached.
WHY IT WORKS 02
Predict shift direction from Q < K or Q > K.
The reaction quotient Q uses the same concentration expression as K but evaluates the system before equilibrium. Comparing Q with K predicts the direction of the net shift: Q below K favors the forward direction, while Q above K favors the reverse direction. Changing concentrations changes Q immediately, whereas changing K requires changing temperature for the reaction represented by this model.
DO NOT MIX THESE UP
Common misconception
Equilibrium does not mean reactions stop. K depends on temperature for a given reaction. Changing concentrations changes Q immediately, not K itself.
PRACTICE CHALLENGE
How does increasing K change the equilibrium fraction of product B?
- Start with K near 1 and note the equilibrium composition.
- Increase K by orders of magnitude.
- Compare the predicted product fraction and shift tendency from the same starting mixture.
Reveal the reasoning
Larger K favors product at equilibrium in this simple 1:1 model. Equilibrium does not mean reactions stop. K depends on temperature for a given reaction. Changing concentrations changes Q immediately, not K itself.
MODEL BOUNDARIES
What this simulation assumes
Every simulation simplifies reality or a mathematical system. These are the assumptions and limits to keep in mind while interpreting the results.
Model assumptions
- The reaction is simplified to a reversible A ⇌ B system with a fixed equilibrium constant K.
- Activities are approximated by concentrations.
- Temperature and total concentration remain fixed unless changed directly.
Model limitations
- Stoichiometries more complex than the implemented one-to-one system are not represented.
- Non-ideal activities, coupled equilibria, phase changes and full thermodynamic calculations are outside the model.
CONNECT IT
Where this matters
- Industrial synthesis
- Acid-base equilibria
- Solubility and complex formation
WORDS THAT MATTER
Key vocabulary
- Equilibrium constant
- Ratio describing equilibrium composition at a given temperature.
- Reaction quotient
- Same concentration expression evaluated away from equilibrium.
- Dynamic equilibrium
- State where forward and reverse rates are equal.
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