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Equilibrium Lab

Investigate chemical equilibrium for the reaction A + B ⇌ C + D. Set initial concentrations, apply Le Chatelier perturbations, and use ICE tables to predict where the system will settle.

Guided Experiment: Le Chatelier's Principle Investigation

If you add more reactant A to a system at equilibrium, what do you predict will happen to the concentrations of C and D?

Write your hypothesis in the Lab Report panel, then click Next.

A (1.00 M)B (1.00 M)
C (0.00 M)D (0.00 M)

Controls

Initial Concentrations (M)
[A]₀1.00 M
[B]₀1.00 M
[C]₀0.00 M
[D]₀0.00 M
Keq4.000
Temperature298 K
Reaction type

Equilibrium Analysis

Forward Shift
Q = 0.0000Keq = 4.0000
Q=0 (all reactants)KeqQ→∞ (all products)
Keq=[C][D][A][B]K_{eq} = \frac{[C][D]}{[A][B]}
ICE Table
[A][B][C][D]
Initial1.0001.0000.0000.000
Change-0.667-0.667+0.667+0.667
Equilibrium0.3330.3330.6670.667
Reaction Quotient Q
0.0000
Keq
4.0000

Concentration vs Time

A (reactant)B (reactant)C (product)D (product)

Data Table

(0 rows)
#Trial[A](M)[B](M)[C](M)[D](M)QKeqShift
0 / 500
0 / 500
0 / 500

Reference Guide

Chemical Equilibrium

A reversible reaction reaches equilibrium when the forward and reverse rates become equal. Concentrations stop changing but both reactions continue at equal rates.

Keq=[C]c[D]d[A]a[B]bK_{eq} = \frac{[C]^c [D]^d}{[A]^a [B]^b}

Keq depends only on temperature, not on initial concentrations or how equilibrium was reached. A large Keq means products are favored; a small Keq means reactants are favored.

Le Chatelier's Principle

When a system at equilibrium is disturbed, it shifts in the direction that partially counteracts the disturbance.

  • Adding reactant shifts the reaction forward
  • Adding product shifts the reaction reverse
  • Raising temperature favors the endothermic direction
  • Lowering temperature favors the exothermic direction

The value of Keq changes only when temperature changes.

ICE Tables

ICE stands for Initial, Change, Equilibrium. The table organizes concentration calculations for a reaction approaching equilibrium.

SpeciesInitialChangeEq.
A[A]₀-x[A]₀-x
C[C]₀+x[C]₀+x

Substitute equilibrium expressions into the Keq equation and solve for x.

Equilibrium Constant

The reaction quotient Q has the same form as Keq but uses current concentrations, not equilibrium concentrations.

  • Q < Keq: reaction shifts forward (products form)
  • Q > Keq: reaction shifts reverse (reactants form)
  • Q = Keq: system is at equilibrium
Q=[C][D][A][B]Q = \frac{[C][D]}{[A][B]}