Reaction Quotient Calculator
The reaction quotient Q from current concentrations, compared against K to tell you which direction the reaction will run.
Q has the same form as the equilibrium constant — products over reactants, each raized to its coefficient — but uses whatever concentrations you have right now rather than the equilibrium ones.
How the reaction quotient calculator works
Q has the same form as the equilibrium constant — products over reactants, each raized to its coefficient — but uses whatever concentrations you have right now rather than the equilibrium ones.
Comparing them gives the direction: Q < K means the reaction runs forward to make more product; Q > K means it runs backward; Q = K means it is already at equilibrium and nothing net happens.
Formula: Q = [C]^c [D]^d / ([A]^a [B]^b)
Worked examples
| Inputs | Reaction quotient Q | Note |
|---|---|---|
| Q below K | 0.8 | runs forward |
| At equilibrium | 1.5 | Q = K exactly |
| Q above K | 12.5 | runs backward |
FAQFrequently asked questions
What is the reaction quotient?
The same expression as the equilibrium constant, but evaluated at the current concentrations rather than the equilibrium ones.
How does comparing Q and K help?
It tells you the direction. Q < K means the system makes more product; Q > K means it consumes it; Q = K means equilibrium.
Is Q the same as K?
Only at equilibrium. That is what equilibrium means.
What does the free-energy figure mean?
RT ln(Q/K) — how far the current state sits from equilibrium in energy terms. Negative means the forward reaction is spontaneous from here.
Do solids and pure liquids count?
No. They are omitted from both Q and K, because their activity is fixed at 1.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- National Institute of Standards and Technology — the US measurement and reference-data authority
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.