Chemical Equilibrium Calculator: Kc, Reaction Quotient Q and ICE Table Solver

Find the equilibrium constant, the direction a reaction will go, or the equilibrium concentrations from an ICE table.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose Kc, Q or an ICE table.

For Kc or Q enter the coefficients from the balanced equation and the concentrations.

For an ICE table enter K and the starting concentrations. The calculator sets up the quadratic, solves it for x and checks the answer by putting it back into K.

Formulas used

  • K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}
  • K_p = K_c(RT)^{\Delta n}
  • Q\ \text{below}\ K:\ \text{shifts right}
  • K = \frac{x^2}{(A_0 - x)(B_0 - x)}

Worked example

With the default numbers in the calculator above:

  1. Expression: products over reactants, each raised to its coefficient: Numerator 0.00081796, denominator 0.0357
  2. Equilibrium constant Kc: 0.022912
  3. Kp at 25 C (pressures in bar), using Kp = Kc (RT) to the change in moles of gas: 0.56798

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: What do you want? Reaction quotient Q and the direction it will go; Equilibrium constant K (Q and ICE cases) 0.5.

  1. Expression: products over reactants, each raised to its coefficient: Numerator 0.00081796, denominator 0.0357
  2. Reaction quotient Q (the same expression with the present concentrations): 0.022912
  3. Compare Q with K: Q is less than K: the reaction shifts to the right, making more products, until Q reaches K.

Common questions

What is an ICE table?

A table of the Initial amounts, the Change and the Equilibrium amounts. It helps you find the equilibrium concentrations when you know K and the starting amounts.

What does the reaction quotient tell me?

Q has the same form as K but uses the concentrations now. If Q is less than K the reaction goes forward. If it is more, it goes back.

Are solids included in K?

No. Pure solids and pure liquids are left out. Only gases and dissolved species appear.

Does changing the concentration change K?

No. K depends only on the temperature.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any first-year chemistry text (chemical equilibrium).

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