Shifting Equilibrium (Le Chatelier)
Aligned to HS-PS1-6 — Next Generation Science Standards.
What this lesson teaches
At equilibrium the forward and reverse reactions run at the same rate, so amounts stop changing. Le Chatelier's principle says that if you stress a system at equilibrium — changing concentration, pressure, or temperature — it shifts in the direction that relieves the stress.
Worked example
For N2 + 3 H2 <-> 2 NH3 (exothermic), adding more N2 stresses the left side, so the equilibrium shifts right to make more ammonia. Increasing pressure also shifts it right, because the right side has fewer gas molecules (2 versus 4) and squeezing favors the smaller-volume side.
Practice questions
- What does it mean for a reaction to be at equilibrium?
- For N2 + 3 H2 <-> 2 NH3, name one condition change that would produce more NH3 and explain why.
- Removing product from an equilibrium mixture: predict which way the equilibrium shifts and justify it with Le Chatelier's principle.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Desplazar el equilibrio (Le Chatelier)
En el equilibrio la reacción directa y la inversa ocurren a la misma velocidad, así que las cantidades dejan de cambiar. El principio de Le Chatelier dice que si perturbas un sistema en equilibrio —cambiando la concentración, la presión o la temperatura— este se desplaza en la dirección que alivia la perturbación.
Ejemplo: Para N2 + 3 H2 <-> 2 NH3 (exotérmica), agregar más N2 perturba el lado izquierdo, así que el equilibrio se desplaza a la derecha para producir más amoníaco. Aumentar la presión también lo desplaza a la derecha, porque el lado derecho tiene menos moléculas de gas (2 frente a 4) y comprimir favorece el lado de menor volumen.
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