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Reaction Quotient and Le Chatelier's Principle

Le Chatelier shifts can be explained precisely with Q and K. A stress (adding a species, changing volume) moves Q away from K; the system then shifts to bring Q back to K. For concentration and volume changes, K stays constant — the shift restores Q to the unchanged K. A temperature change is different: it changes K itself.

UNIT 7 TOPIC 7.10 • REACTION QUOTIENT AND LE CHATELIER'S PRINCIPLE SHIFT EXPLAINER CONCENTRATION STRESS K stays constant STRESS add A INSTANTLY Q < K SHIFT right NEW EQ. Q = K A + B ⇌ C Q = [C] [A] [B] ← add A raises the denominator Adding A raises the denominator of Q, so Q drops below K. The reaction shifts right, forming products until Q = K again. K is UNCHANGED — a concentration stress never changes the value of K. TEMPERATURE STRESS K itself changes K temperature (T) K rises as T rises → endothermic A concentration or pressure stress changes Q first, and Q settles back to the same K. A temperature change is different — it changes the value of K itself. Here K rises with T, so heat acts like a reactant: an endothermic case. CED ANCHOR Le Chatelier shifts are explained with Q and K: most stresses change Q (K is unchanged); a temperature change moves K itself. AP Chemistry · Unit 7 · Equilibrium
A Le Chatelier shift is really a Q-versus-K story. A stress moves Q away from K; the system then shifts to bring Q back to K. K itself stays constant when the stress is a concentration or volume change — only a temperature change alters K.
Shift Explainer · Open the sandbox →

The trap assumes temperature leaves K fixed. Temperature is the one stress that does change K (shifting the target), whereas concentration and volume stresses move Q toward an unchanged K. Distinguish which stress moves Q and which moves K.

The work

3 ways in · any order
Lesson
Q and Le Chatelier ›

A stress moves Q from K, and the system shifts Q back — with K fixed for concentration/volume but changed by temperature. The lesson reasons via Q and K, then closes with a ten-scenario check.

Skill check · 10 scenarios
Open lesson →
Diagnostic
10-item topic check ›

Ten items spanning the Topic 7.10 misconception: temperature assumed to leave K fixed, when temperature is the stress that changes K.

Not started · 10 items · ~15 min
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Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

Take the diagnostic to identify your misconceptions
Diagnostic first