Le Chatelier's Principle Examples: 44 Problems with Answers
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 — such as a change in concentration, pressure, or temperature — the equilibrium shifts in the direction that relieves the stress.
Push on equilibrium, and it pushes back. Add something, and the system uses it up.
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
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
2
Stresses include changes in concentration, pressure, or temperature.
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+3H2⇌2NH3+heat, predict the effect of: (a) increasing temperature, (b) removing NH3, (c) increasing pressure.
Example 3
medium
For 2SO2(g)+O2(g)⇌2SO3(g), ΔH<0. Predict the shift for: (a) adding O2, (b) raising T, (c) raising P, (d) removing SO3.
Example 4
medium
For 2NO(g)+O2(g)⇌2NO2(g), ΔH<0. Predict the effect on yield of: (a) raising T, (b) increasing P, (c) removing NO2.
Example 5
hard
For PCl5(g)⇌PCl3(g)+Cl2(g) at equilibrium, the volume is suddenly halved. (a) What does Qc become immediately, in terms of Kc? (b) Predict the shift.Halving container volume raises pressure — Qc = 2Kc so equilibrium shifts left toward PCl₅
Example 6
hard
In a sealed flask, N2O4(g)⇌2NO2(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)⇌2NH3(g), ΔH=−92kJ. 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)⇌CaO(s)+CO2(g) (endothermic), predict the effect of increasing temperature on the amount of CO2 produced.Increasing temperature shifts this endothermic equilibrium right, producing more CO₂
Example 2
hard
The contact process produces sulfur trioxide: 2SO2(g)+O2(g)⇌2SO3(g), ΔH=−198kJ. Explain why the industrial process uses: (a) high pressure, (b) moderate temperature (450°C) rather than low temperature, and (c) a V2O5 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)⇌C(g) (2 mol gas → 1 mol gas), increasing pressure shifts equilibrium which way?Increasing pressure favors the side with fewer moles of gas — equilibrium shifts toward product C
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+3H2⇌2NH3, increasing pressure favors which side?Increasing pressure shifts equilibrium toward NH₃ (fewer moles of gas on product side)
Example 11
medium
For endothermic A⇌B (heat +A⇌B), predict the shift when temperature is raised, and what happens to K.
Example 12
medium
In 2NO2⇌N2O4, the system is compressed (volume halved). Predict the shift and explain.Compressing the container (volume halved) shifts equilibrium toward N₂O₄ (2 mol → 1 mol gas)
Example 13
medium
For A(g)⇌2B(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+3H2⇌2NH3 (exothermic), why is a compromise moderate temperature used instead of low temperature?
Example 15
medium
Adding more O2 to 2SO2+O2⇌2SO3 at equilibrium does what to [SO3]?
Example 16
medium
For exothermic 2SO2+O2⇌2SO3, list how to maximize SO3 yield using concentration, pressure, and temperature.
Example 17
medium
Why does changing concentration shift the equilibrium position but NOT change K, while changing temperature changes K?
Example 18
challenge
For exothermic N2+3H2⇌2NH3, you simultaneously raise temperature and pressure. Predict the competing effects on NH3 yield.
Example 19
challenge
A student claims adding a catalyst to N2+3H2⇌2NH3 will increase the equilibrium amount of NH3. Is this correct? Explain.
Example 20
challenge
For C(s)+CO2(g)⇌2CO(g), increasing pressure shifts which way? Be careful about phases.Increasing pressure shifts toward fewer gas moles — left (CO₂ side), ignoring solid C
Example 21
medium
In 2NO2(brown)⇌N2O4(colorless) (forward exothermic), the gas darkens when heated. Explain using Le Chatelier.Heating shifts the exothermic forward reaction left, producing more brown NO₂ and darkening the gas
Example 22
medium
Endothermic A⇌B has K=2 at 300K. Predict whether K at 350K is larger or smaller than 2, and the direction of shift on heating.
Example 23
easy
For N2(g)+3H2(g)⇌2NH3(g), what happens if H2 is added to the equilibrium mixture?
Example 24
easy
For 2NO2(g)⇌N2O4(g), predict the shift when the volume of the container is decreased (pressure increased).Decreasing container volume increases pressure — equilibrium shifts right toward N₂O₄
Example 25
easy
For an endothermic reaction, A⇌B with ΔH>0, what does increasing temperature do?
Example 26
medium
For the Haber process N2(g)+3H2(g)⇌2NH3(g), ΔH=−92kJ. Why is the process run at high pressure but only moderate temperature (∼450∘C)?
Example 27
medium
For CaCO3(s)⇌CaO(s)+CO2(g), predict the effect of (a) removing CO2, (b) adding more CaCO3.
Example 28
medium
For N2O4(g)⇌2NO2(g), ΔH>0. When the temperature is raised, what happens to (a) Kc and (b) the equilibrium [NO2]?
Example 29
medium
For the equilibrium Fe3+(aq)+SCN−(aq)⇌FeSCN2+(aq) (red), adding Fe3+ causes what visible change?
Example 30
medium
For COCl2(g)⇌CO(g)+Cl2(g), doubling the container volume causes what shift?Doubling the container volume lowers pressure — equilibrium shifts right toward CO + Cl₂ (more gas moles)
Example 31
medium
For CO(g)+H2O(g)⇌CO2(g)+H2(g), does compressing the gas mixture shift the equilibrium?
Example 32
hard
A reaction has Kc=10 at 300 K and Kc=1 at 500 K. Is the reaction endothermic or exothermic?
Example 33
hard
For CH4(g)+H2O(g)⇌CO(g)+3H2(g), ΔH>0. To maximize H2 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)⇌Ag+(aq)+Cl−(aq), adding NaCl(aq) has what effect on the solubility of AgCl?
Example 35
medium
For CH3COOH(aq)⇌H+(aq)+CH3COO−(aq), adding sodium acetate causes what change in pH?
Example 36
medium
For CO2(g)+H2O(l)⇌H2CO3(aq), opening a carbonated drink bottle causes what shift?
Example 37
hard
For 2HI(g)⇌H2(g)+I2(g) (Δn=0), removing some H2 shifts the equilibrium which way? Does K change?