What happens to K when the equation changes?
You will be able to: Transform K and Q when reversing or scaling a balanced equation.
What happens to K when the equation changes?
Reading a ratio backward changes 4-to-1 into 1-to-4. Writing a chemical equation backward also reverses the numerator and denominator in its equilibrium expression.
A useful starting point: Does a large K mean a fast reaction? →
Words and symbols before equations
- Reciprocal
- One divided by a number, such as 1/4.
- Scale factor
- Multiplier applied to every coefficient.
- Power rule
- Raising the whole expression to the coefficient scale factor.
- Reaction convention
- The exact balanced equation to which K refers.
What this picture assumes
Original A ⇌ B has K=4 at fixed T. Scale all coefficients and optionally reverse. K changes because the written equation changes, not because the physical equilibrium changes.
Read the picture in three steps
- Read the species and labels first. Identify what each symbol and line represents. Read the units and fixed conditions before comparing quantities.
- The transformed constant is 16 at the same temperature. Identical power/reciprocal rules apply to a current Q.
- Check what the picture assumes below. Use the Explore task to predict one change before moving a control.
Connect the picture to the chemistry
For A ⇌ B, K=[B]/[A]. Reversing to B ⇌ A makes K′=[A]/[B]=1/K.
Doubling to 2A ⇌ 2B squares every concentration term, so K′=K². Halving coefficients takes the square root.
Reversing does not make K negative. Do not confuse these operations with reaction enthalpy, which changes sign on reversal and scales linearly.
Q has the same algebraic form, so the identical reciprocal and power operations apply to Q for a fixed composition. These transformations keep the temperature fixed.
A worked example, step by step
A ⇌ B has K=4. Find K for 2A ⇌ 2B and then for 2B ⇌ 2A.
- Doubling coefficients squares the original expression.
- Kdouble=4²=16.
- Reversing that doubled equation takes the reciprocal.
- Kreverse,double=1/16=0.0625; it remains positive.
Multiplying coefficients by two does not multiply K by two.
If K=9, what is K for the half-scaled forward equation?
Compare with an explanation
√9=3, because every exponent is halved.
Predict. Change one thing. Explain.
Change the coefficient scale and direction. Compare K′ to the displayed transformed equation; test a half-scale reversal.
On narrow screens, swipe or scroll diagrams sideways to read all labels.
The transformed constant is 16 at the same temperature. Identical power/reciprocal rules apply to a current Q.
Original A ⇌ B has K=4 at fixed T. Scale all coefficients and optionally reverse. K changes because the written equation changes, not because the physical equilibrium changes.
Explain what you noticed: Answer the investigation prompt above. State one observation and explain it using relative rates, particle conservation, the Q/K comparison or the stated dissolution equilibrium. Identify what the representation cannot tell you.
Apply the idea to a fresh problem Practice →Show what you understand.
Two original questions are a starting check, not proof of mastery. Explain your choice before revealing the answer.
Original written challenge
4 points · self-check · not an official AP questionA ⇌ B has K=16 and a current Q=4. Write K′ and Q′ for ½B ⇌ ½A and explain why both operations match.
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Compare with the answer and four-point rubric
- 1 point: Reverse the equation and halve all coefficients.
- 1 point: K′=(1/16)^(1/2)=0.25.
- 1 point: Q′=(1/4)^(1/2)=0.50.
- 1 point: Q and K share the same expression, so both transform by inverse square root.
Accept equivalent correct methods and explanations. This is a Refresh Kid teaching rubric, not an official AP scoring guideline.
Retrieve it before you reveal it.
RECALL 1Does reversing make K negative?
No; it gives 1/K.
RECALL 2Why does doubling square K?
Every concentration or pressure exponent doubles.
RECALL 3Do the rules apply to Q?
Yes, because Q has the same algebraic form.
Revisit these tomorrow and a week later. Try a fresh problem and explain why the method applies.
What happens to K when the equation changes?
- Reverse: K′=1/K.
- Scale coefficients by n: K′=Kⁿ; identical rules apply to Q.
Remember: Multiplying coefficients by two does not multiply K by two.
Conditions: Original A ⇌ B has K=4 at fixed T. Scale all coefficients and optionally reverse. K changes because the written equation changes, not because the physical equilibrium changes.
Refresh Kid · AP Chemistry Unit 7 · Objectives 7.6.A · Review edition
Framework, scope and review status
Mapped to College Board CED, Topic 7.6, objective 7.6.A. CED effective Fall 2024 and June 2026 clarifications checked September 17, 2026. Unit 7: Equilibrium, Topics 7.1–7.12. Focused lesson names, examples, models and assessments are original Refresh Kid teaching materials, not additional official topics or official AP questions. Official corrections.
The model states its assumptions beside the diagram. Converting between Kc and Kp and calculations for a dissolved species in equilibrium with its gas phase are excluded from assessed Unit 7 scope. Concentrations use mol/L and gas partial pressures use the stated pressure convention. Supplied constants are teaching data at fixed temperature unless otherwise specified. Ideal dilute-solution and ideal-gas approximations are stated. 3D views show inventories, not molecular trajectories, measured structures or proof of equilibrium from a single snapshot. Approximation checks are explicit; a small K alone does not justify neglecting every change.
Teaching resources: The Organic Chemistry Tutor video titles/descriptions and topic coverage were checked for optional links; no claim is made to have watched every video. No creator scripts, examples, worksheets or artwork were copied. GitHub’s 3D website collection and its Three.js camera-control example informed the idea of controllable spatial inspection. Scientific diagrams, geometry and interactions here are original. The self-hosted Three.js runtime retains its MIT license. Camera rotation changes the view, not the chemistry.
Independent teacher review and observation of students remain pending. Implementation checks do not certify scientific accuracy, accessibility or learning effectiveness. This is a review edition.
Optional official resource: Released AP Chemistry questions and scoring guides. This archive contains questions across units; it is not an assignment of every question to this lesson.
The teaching sequence is informed by the IES learning guide; this exact implementation has not been evaluated with learners.
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