Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

7.3Equilibrium

Le Châtelier’s Principle — AP CHEMISTRY Revision Notes & Topical Questions

5 min read 9 parts Lesson 10 of 19 1 quiz

📚 AP CHEMISTRY Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
0%read
Lesson summary

7.3 Le Châtelier's Principle — AP CHEMISTRY notes: Predict equilibrium shifts for concentration, volume, pressure and temperature changes and relate them to Q and K.Statement — a system at equilibrium shifts to partially counteract an applied stressStresses — addition or removal …

  • Temperature rise
  • Temperature fall
  • After a stress
  • Pressure doubled
  • Equilibrium position
  • Reaction quotient

Part 1 of 7Principle

Statement
  • Statement a system at equilibrium shifts to partially counteract an applied stress
Stresses
  • Stresses addition or removal of a species, dilution, volume or pressure change in gas systems, and temperature change

Part 2 of 7Effect of adding or removing a species

StressShiftEffect
Add reactantForwardReactants converted to products
Add productReverseProducts converted to reactants
Remove reactantReverseProducts converted to reactants
Remove productForwardReactants converted to products

Part 3 of 7Gases and dilution

StressShift
Higher pressure (smaller volume)Fewer moles of gas
Lower pressure (larger volume)More moles of gas
Dilution of aqueous systemMore moles of aqueous particles
Pure solid or liquid added or removedNone

Part 4 of 7Temperature

Temperature rise
  • Temperature rise endothermic direction favoured
Temperature fall
  • Temperature fall exothermic direction favoured
K changes
  • K changes only a temperature change alters K

Part 5 of 7Using Q

After a stress
  • Q is compared with KQ < K shifts forward and Q > K shifts in reverse
Catalyst
  • Catalyst no shift and no change in K because both rates increase equally

Part 6 of 7Example: PCl₃ + Cl₂ ⇌ PCl₅

Pressure doubled
  • Pressure doubled shift toward the fewer moles of gas (PCl5), so P(PCl5) increases
Kp
  • Kp unchanged at constant temperature

Part 7 of 7More from the specification

More from the specification
Ionic dissociation in electrolyte solution
  • Ionic dissociation in electrolyte solution polar water molecules surround dissociated ions, forming a conducting aqueous electrolyte solution.
Reaction quotient
  • The ratio of product to reactant concentrations at any moment.
pH
-log[H+]
What the symbols mean: pH has no unit · [H+] = concentration of hydrogen ions (mol dm−3); each 1 pH unit is a ten-fold change in [H+]

Key terms

TermMeaning
Le Châtelier's principleSystems at equilibrium oppose applied stresses.
Equilibrium positionRelative amounts of products and reactants.
StressChange applied to a system at equilibrium.
Reaction quotientQ, compared with K to find the direction of shift.

Avoid these mistakes

Avoid these mistakes
Believing a shift undoes the stress completely — it only partly counteracts it.
Saying volume changes affect aqueous systems.
Saying adding a catalyst increases the yield.

Last updated:

\n