Le Chatelier's Principle Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Le Chatelier's Principle.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

When a system at chemical equilibrium is subjected to an external stress β€” such as a change in concentration, pressure, or temperature β€” the equilibrium.

Push on equilibrium, and it pushes back. Add something, and the system uses it up.

Read the full concept explanation β†’

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Le Chatelier's Principle starts by naming the reversible reaction, the stress, and which side is favored.

Common stuck point: Students often know a formula related to le chatelier's principle but skip the recognition step: Am I reasoning about a reversible reaction where forward and reverse processes continue and a stress shifts the composition? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I reasoning about a reversible reaction where forward and reverse processes continue and a stress shifts the composition?

Worked Examples

Example 1

easy
State Le Chatelier's principle and explain what it predicts about equilibrium systems.

Answer

AΒ systemΒ atΒ equilibriumΒ shiftsΒ toΒ opposeΒ anyΒ appliedΒ stress.\text{A system at equilibrium shifts to oppose any applied stress.}

First step

1
Le Chatelier's principle states: if a system at equilibrium is subjected to a change (stress), the system will shift to partially counteract that change and establish a new equilibrium.

Full solution

  1. 2
    Stresses include changes in concentration, pressure, or temperature.
  2. 3
    The system responds by shifting the equilibrium position (favoring either the forward or reverse reaction) to reduce the effect of the disturbance.
Le Chatelier's principle is a qualitative tool for predicting how an equilibrium system responds to changes. It does not tell us the exact new concentrations, but it tells us the direction of the shift.

Example 2

medium
For the exothermic reaction N2+3H2β‡Œ2NH3+heat\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3 + \text{heat}, predict the effect of: (a) increasing temperature, (b) removing NH3\text{NH}_3, (c) increasing pressure.

Example 3

medium
For 2SO2(g)+O2(g)β‡Œ2SO3(g)2\text{SO}_2(g)+\text{O}_2(g)\rightleftharpoons 2\text{SO}_3(g), Ξ”H<0\Delta H<0. Predict the shift for: (a) adding O2\text{O}_2, (b) raising T, (c) raising P, (d) removing SO3\text{SO}_3.

Example 4

medium
For 2NO(g)+O2(g)β‡Œ2NO2(g)2\text{NO}(g)+\text{O}_2(g)\rightleftharpoons 2\text{NO}_2(g), Ξ”H<0\Delta H<0. Predict the effect on yield of: (a) raising T, (b) increasing P, (c) removing NO2\text{NO}_2.

Example 5

hard
For PCl5(g)β‡ŒPCl3(g)+Cl2(g)\text{PCl}_5(g)\rightleftharpoons \text{PCl}_3(g)+\text{Cl}_2(g) at equilibrium, the volume is suddenly halved. (a) What does QcQ_c become immediately, in terms of KcK_c? (b) Predict the shift.

Example 6

hard
In a sealed flask, N2O4(g)β‡Œ2NO2(g)\text{N}_2\text{O}_4(g)\rightleftharpoons 2\text{NO}_2(g) is at equilibrium and brown. The flask is plunged into an ice bath and the gas becomes paler. Is the forward reaction exothermic or endothermic?

Example 7

challenge
For the synthesis N2(g)+3H2(g)β‡Œ2NH3(g)\text{N}_2(g)+3\text{H}_2(g)\rightleftharpoons 2\text{NH}_3(g), Ξ”H=βˆ’92 kJ\Delta H=-92\,\text{kJ}. The Haber process uses a catalyst. Explain why a catalyst is necessary even though it doesn't shift equilibrium.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
For the equilibrium CaCO3(s)β‡ŒCaO(s)+CO2(g)\text{CaCO}_3\text{(s)} \rightleftharpoons \text{CaO(s)} + \text{CO}_2\text{(g)} (endothermic), predict the effect of increasing temperature on the amount of CO2\text{CO}_2 produced.

Example 2

hard
The contact process produces sulfur trioxide: 2SO2(g)+O2(g)β‡Œ2SO3(g)2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{SO}_3\text{(g)}, Ξ”H=βˆ’198 kJ\Delta H = -198\,\text{kJ}. Explain why the industrial process uses: (a) high pressure, (b) moderate temperature (450Β°C450Β°\text{C}) rather than low temperature, and (c) a V2O5\text{V}_2\text{O}_5 catalyst.

Example 3

easy
Le Chatelier's principle: if you add more reactant to a system at equilibrium, which way does it shift?

Example 4

easy
If you remove a product from a system at equilibrium, which way does it shift?

Example 5

easy
For A(g)+B(g)β‡ŒC(g)\text{A(g)}+\text{B(g)}\rightleftharpoons\text{C(g)} (2 mol gas β†’\rightarrow 1 mol gas), increasing pressure shifts equilibrium which way?

Example 6

easy
Adding an inert gas at constant volume changes the total pressure. Does it shift the equilibrium position?

Example 7

easy
Does adding a catalyst shift the equilibrium position?

Example 8

easy
For an exothermic reaction at equilibrium, does cooling shift it toward reactants or products?

Example 9

easy
Does the system fully cancel an applied stress, or only partly?

Example 10

easy
For N2+3H2β‡Œ2NH3\text{N}_2+3\text{H}_2\rightleftharpoons2\text{NH}_3, increasing pressure favors which side?

Example 11

medium
For endothermic Aβ‡ŒB\text{A}\rightleftharpoons\text{B} (heat +Aβ‡ŒB+\text{A}\rightleftharpoons\text{B}), predict the shift when temperature is raised, and what happens to KK.

Example 12

medium
In 2NO2β‡ŒN2O42\text{NO}_2\rightleftharpoons\text{N}_2\text{O}_4, the system is compressed (volume halved). Predict the shift and explain.

Example 13

medium
For A(g)β‡Œ2B(g)\text{A(g)}\rightleftharpoons2\text{B(g)}, the number of gas moles increases left to right. Does decreasing pressure favor reactant or product?

Example 14

medium
In the Haber process N2+3H2β‡Œ2NH3\text{N}_2+3\text{H}_2\rightleftharpoons2\text{NH}_3 (exothermic), why is a compromise moderate temperature used instead of low temperature?

Example 15

medium
Adding more O2\text{O}_2 to 2SO2+O2β‡Œ2SO32\text{SO}_2+\text{O}_2\rightleftharpoons2\text{SO}_3 at equilibrium does what to [SO3][\text{SO}_3]?

Example 16

medium
For exothermic 2SO2+O2β‡Œ2SO32\text{SO}_2+\text{O}_2\rightleftharpoons2\text{SO}_3, list how to maximize SO3\text{SO}_3 yield using concentration, pressure, and temperature.

Example 17

medium
Why does changing concentration shift the equilibrium position but NOT change KK, while changing temperature changes KK?

Example 18

challenge
For exothermic N2+3H2β‡Œ2NH3\text{N}_2+3\text{H}_2\rightleftharpoons2\text{NH}_3, you simultaneously raise temperature and pressure. Predict the competing effects on NH3\text{NH}_3 yield.

Example 19

challenge
A student claims adding a catalyst to N2+3H2β‡Œ2NH3\text{N}_2+3\text{H}_2\rightleftharpoons2\text{NH}_3 will increase the equilibrium amount of NH3\text{NH}_3. Is this correct? Explain.

Example 20

challenge
For C(s)+CO2(g)β‡Œ2CO(g)\text{C(s)}+\text{CO}_2\text{(g)}\rightleftharpoons2\text{CO(g)}, increasing pressure shifts which way? Be careful about phases.

Example 21

medium
In 2NO2(brown)β‡ŒN2O4(colorless)2\text{NO}_2\text{(brown)}\rightleftharpoons\text{N}_2\text{O}_4\text{(colorless)} (forward exothermic), the gas darkens when heated. Explain using Le Chatelier.

Example 22

medium
Endothermic Aβ‡ŒB\text{A}\rightleftharpoons\text{B} has K=2K=2 at 300 K300\,\text{K}. Predict whether KK at 350 K350\,\text{K} is larger or smaller than 2, and the direction of shift on heating.

Example 23

easy
For N2(g)+3H2(g)β‡Œ2NH3(g)\text{N}_2(g)+3\text{H}_2(g)\rightleftharpoons 2\text{NH}_3(g), what happens if H2\text{H}_2 is added to the equilibrium mixture?

Example 24

easy
For 2NO2(g)β‡ŒN2O4(g)2\text{NO}_2(g)\rightleftharpoons \text{N}_2\text{O}_4(g), predict the shift when the volume of the container is decreased (pressure increased).

Example 25

easy
For an endothermic reaction, Aβ‡ŒB\text{A}\rightleftharpoons \text{B} with Ξ”H>0\Delta H>0, what does increasing temperature do?

Example 26

medium
For the Haber process N2(g)+3H2(g)β‡Œ2NH3(g)\text{N}_2(g)+3\text{H}_2(g)\rightleftharpoons 2\text{NH}_3(g), Ξ”H=βˆ’92 kJ\Delta H=-92\,\text{kJ}. Why is the process run at high pressure but only moderate temperature (∼450∘C\sim 450^\circ\text{C})?

Example 27

medium
For CaCO3(s)β‡ŒCaO(s)+CO2(g)\text{CaCO}_3(s)\rightleftharpoons \text{CaO}(s)+\text{CO}_2(g), predict the effect of (a) removing CO2\text{CO}_2, (b) adding more CaCO3\text{CaCO}_3.

Example 28

medium
For N2O4(g)β‡Œ2NO2(g)\text{N}_2\text{O}_4(g)\rightleftharpoons 2\text{NO}_2(g), Ξ”H>0\Delta H>0. When the temperature is raised, what happens to (a) KcK_c and (b) the equilibrium [NO2][\text{NO}_2]?

Example 29

medium
For the equilibrium Fe3+(aq)+SCNβˆ’(aq)β‡ŒFeSCN2+(aq)\text{Fe}^{3+}(aq)+\text{SCN}^-(aq)\rightleftharpoons \text{FeSCN}^{2+}(aq) (red), adding Fe3+\text{Fe}^{3+} causes what visible change?

Example 30

medium
For COCl2(g)β‡ŒCO(g)+Cl2(g)\text{COCl}_2(g)\rightleftharpoons \text{CO}(g)+\text{Cl}_2(g), doubling the container volume causes what shift?

Example 31

medium
For CO(g)+H2O(g)β‡ŒCO2(g)+H2(g)\text{CO}(g)+\text{H}_2\text{O}(g)\rightleftharpoons \text{CO}_2(g)+\text{H}_2(g), does compressing the gas mixture shift the equilibrium?

Example 32

hard
A reaction has Kc=10K_c=10 at 300 K and Kc=1K_c=1 at 500 K. Is the reaction endothermic or exothermic?

Example 33

hard
For CH4(g)+H2O(g)β‡ŒCO(g)+3H2(g)\text{CH}_4(g)+\text{H}_2\text{O}(g)\rightleftharpoons \text{CO}(g)+3\text{H}_2(g), Ξ”H>0\Delta H>0. To maximize H2\text{H}_2 yield, should the industrial process run (a) at high or low T and (b) at high or low P?

Example 34

medium
For AgCl(s)β‡ŒAg+(aq)+Clβˆ’(aq)\text{AgCl}(s)\rightleftharpoons \text{Ag}^+(aq)+\text{Cl}^-(aq), adding NaCl(aq)\text{NaCl}(aq) has what effect on the solubility of AgCl?

Example 35

medium
For CH3COOH(aq)β‡ŒH+(aq)+CH3COOβˆ’(aq)\text{CH}_3\text{COOH}(aq)\rightleftharpoons \text{H}^+(aq)+\text{CH}_3\text{COO}^-(aq), adding sodium acetate causes what change in pH?

Example 36

medium
For CO2(g)+H2O(l)β‡ŒH2CO3(aq)\text{CO}_2(g)+\text{H}_2\text{O}(l)\rightleftharpoons \text{H}_2\text{CO}_3(aq), opening a carbonated drink bottle causes what shift?

Example 37

hard
For 2HI(g)β‡ŒH2(g)+I2(g)2\text{HI}(g)\rightleftharpoons \text{H}_2(g)+\text{I}_2(g) (Ξ”n=0\Delta n=0), removing some H2\text{H}_2 shifts the equilibrium which way? Does KK change?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

equilibrium