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SCIENCE · INVESTIGATE AND EXPLAIN

Transform equilibrium constants with exact reaction statements

A constant is not a property of a chemical name alone; the complete written equation matters.

Learning outcome: Derive each transformation by multiplying or inverting activity quotients. Compare formal coefficient scaling with a real concentration perturbation.

Starting recap

Refresh dimensionless activities, component balances, admissible roots, normalized partial pressures and independent versus shared measurement errors.

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Try

For A⇌B with K1=4 and B⇌C with K2=3, A⇌C has K=12, B⇌A has .25, and 2A⇌2B has 16.

Open the experiment

Predict

Does doubling a written reaction make the physical sample twice as product-rich?

Experiment

Derive each transformation by multiplying or inverting activity quotients. Compare formal coefficient scaling with a real concentration perturbation.

Transform a constant together with its reaction

Worked teaching model · synthetic values · Fictional isomer reactions at one temperature and compatible activity standard states. Reverse inverts K, multiply coefficients by two squares K, add reactions multiplies constants. Changing notation does not create a new physical mixture.

Reset keeps your prediction, captures and practice history.

transformed Kreaction coefficient multiplier02160
  • K for coefficients multiplied by lambda: solid

Axes rescale. A quotient comparison, inventory intersection and relaxation trajectory have different horizontal meanings; inspect labels rather than treating every curve as elapsed time.

All calculated plot coordinates
K for coefficients multiplied by lambda
reaction coefficient multipliertransformed K
01
0.033333331.047294
0.066666671.096825
0.11.148698
0.13333331.203025
0.16666671.259921
0.21.319508
0.23333331.381913
0.26666671.447269
0.31.515717
0.33333331.587401
0.36666671.662476
0.41.741101
0.43333331.823445
0.46666671.909683
0.52
0.53333332.094588
0.56666672.19365
0.62.297397
0.63333332.40605
0.66666672.519842
0.72.639016
0.73333332.763826
0.76666672.894538
0.83.031433
0.83333333.174802
0.86666673.324952
0.93.482202
0.93333333.64689
0.96666673.819366
14
1.0333334.189176
1.0666674.3873
1.14.594793
1.1333334.8121
1.1666675.039684
1.25.278032
1.2333335.527652
1.2666675.789077
1.36.062866
1.3333336.349604
1.3666676.649903
1.46.964405
1.4333337.29378
1.4666677.638733
1.58
1.5333338.378353
1.5666678.7746
1.69.189587
1.6333339.6242
1.66666710.07937
1.710.55606
1.73333311.0553
1.76666711.57815
1.812.12573
1.83333312.69921
1.86666713.29981
1.913.92881
1.93333314.58756
1.96666715.27747
216
Calculated under the declared model
QuantityValueUnit
A to B constant4dimensionless
B to A constant0.25dimensionless
2A to 2B constant16dimensionless
A to C coupled constant12dimensionless
C to A coupled reverse constant0.08333333dimensionless

A constant belongs to an exact written reaction and its standard-state convention.

Multiply activity quotients when adding reactions so intermediate activities cancel. Do not add K values, and do not compare the magnitude of K for differently scaled reactions as evidence that one physical mixture is more complete. Fractional scaling is a formal thermodynamic transformation, not a fractional molecule event.

These calculated packets are not performed chemical measurements. Keep feasible inventories, activity conventions, fitting observations and independent checks distinct.

A constant belongs to an exact written reaction and its standard-state convention.

Multiply activity quotients when adding reactions so intermediate activities cancel. Do not add K values, and do not compare the magnitude of K for differently scaled reactions as evidence that one physical mixture is more complete. Fractional scaling is a formal thermodynamic transformation, not a fractional molecule event.

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Attach K to an equation

Suppose ideal isomers satisfy a_B/a_A=4 at equilibrium. Reversing the written equation gives a_A/a_B=1/4. Doubling it gives a_B²/a_A²=16. The same physical mixture satisfies all three expressions. No molecule needs to react twice merely because we rescaled the bookkeeping.

Eliminate a shared intermediate

For A⇌B with K1 and B⇌C with K2, multiply the quotients: (a_B/a_A)(a_C/a_B)=a_C/a_A. Thus the summed reaction A⇌C has K1K2. This requires the same temperature and compatible standard states so that the intermediate activity really is the same quantity in both expressions.

At K1=4 and K2=3, the coupled constant is 12, not 7. Reversing the combined equation gives 1/12. Multiplying the entire combined equation by one half gives the square root of 12 as a formal thermodynamic transformation, not an elementary half-molecule collision.

Check interpretation rather than magnitude alone

A large number after coefficient scaling does not demonstrate a larger conversion in a previously unchanged sample. Conversion still requires a specified initial inventory and feasible equilibrium composition. A constant also does not identify a kinetic pathway.

Transfer and check

Let X⇌Y have K=5 and Y⇌Z have K=2. Predict the constant for 2Z⇌2X, explaining each algebraic operation. The coupled forward constant is 10; reverse and square to obtain .0100. Write the corresponding activity quotient and verify that the intermediate Y cancels.

Source and evidence boundary

Conceptual reference checked 30 October 2026: OpenStax Chemistry 2e. These original hypothetical packets use explicitly defined activities, inventories and response assumptions. No material is mixed, heated, pressurized or measured. Numerical compatibility does not certify practical technique or uniquely establish a real chemical mechanism. Retain your prediction, feasible inventory, quotient check and changed-case interpretation.

Apply

If A⇌B has K=4, the constant for 2B⇌2A is:

Public practice checks a specific claim. It does not establish independent mastery.

Why is comparing K magnitudes across differently scaled reaction equations misleading?

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