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Equilibrium Constant Calculator

Enter the coefficients and concentrations in their designated fields. The calculator will instantly calculate the equilibrium constant by using its respective chemical equation.

By Using:

pressure [A]:

M ▾

Pressure a:

pressure [B]:

M ▾

Pressure b:

pressure [C]:

M ▾

Pressure c:

pressure [D]:

M ▾

Pressure d:

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Equilibrium Constant Calculator

The equilibrium constant calculator helps understand reversible chemical reactions. Depending on the molar concentrations of reactants and products, the reaction can proceed forward or backward. This calculator also determines how much of each substance remains at equilibrium and estimates the time required to reach it.

Definition of the Equilibrium Constant

“The equilibrium constant (Kc) is the ratio that describes how a reaction progresses in the forward and reverse directions, indicating the relative concentrations of reactants and products at equilibrium.”

At equilibrium, the forward reaction rate (Kf) equals the reverse reaction rate (Kr). Using the equilibrium constant calculator helps determine both the direction and extent of a chemical reaction.

Equilibrium Constant Equation

For a general reaction:

a[A] + b[B] ⇌ c[C] + d[D]

Equilibrium constant (Kc):

Kc = ([C]^c × [D]^d) / ([A]^a × [B]^b)

Also, Kc = Kf / Kr

Graphical Representation of Kc

Example: the production of nitrogen dioxide (NO₂) from dinitrogen tetroxide (N₂O₄):

(N₂O₄)_g ⇌ (NO₂)_g

Graphical representation of Kc

The concentrations of NO₂ and N₂O₄ reach equilibrium over time. Using a calculator, we can find Kc and predict when the equilibrium stage is achieved.

Effect of Kc Value on Reaction

Example: CO₂ + H₂ ⇌ CO + H₂O in a 3 L vessel:

CO₂ = 0.1908 mol
H₂ = 0.0908 mol
CO = 0.009 mol
H₂O = 0.0092 mol

Convert to molar concentrations:

[CO₂] = 0.1908 / 3 = 0.0636 M
[H₂] = 0.0908 / 3 = 0.0303 M
[CO] = 0.009 / 3 = 0.003 M
[H₂O] = 0.0092 / 3 = 0.0031 M

Kc = ([CO][H₂O]) / ([CO₂][H₂]) = (0.003 × 0.0031) / (0.0636 × 0.0303) = 4.825 × 10^-4

Calculating Kc Using ICE Table

Example: I₂(aq) + I^-(aq) ⇌ I₃^-(aq)

Initial concentrations: [I₂] = [I^-] = 1.00 × 10^-3 M, [I₃^-] = 0. Equilibrium [I₂] = 6.61 × 10^-4 M.

	I₂ (aq)	I^- (aq)	I₃^- (aq)
Initial (M)	1 × 10^-3	1 × 10^-3	0
Change (M)	-x	-x	+x
Equilibrium (M)	1 × 10^-3 - x	1 × 10^-3 - x	x

x = 1 × 10^-3 - 6.61 × 10^-4 = 3.39 × 10^-4 M

Kc = [I₃^-] / ([I₂][I^-]) = 3.39 × 10^-4 / (6.61 × 10^-4 × 6.61 × 10^-4) ≈ 766

Uses of Kc

Kc = 0: System is at equilibrium; no net reaction.
Kc > 0: Reaction favors products (forward direction).
Kc < 0: Reaction favors reactants (reverse direction).

Types of Chemical Reactions

Homogeneous Reactions – reactants in the same phase (e.g., CO(g) + H₂(g) ⇌ CH₃OH(g))
Heterogeneous Reactions – reactants in different phases (e.g., C(s) + O₂(g) ⇌ CO₂(g))

Extent of Reaction (Kc)

High Kc → reaction favors products, essentially complete at equilibrium.
Low Kc → reaction favors reactants, little product formed.
Moderate Kc → significant amounts of both reactants and products at equilibrium.

How the Equilibrium Constant Calculator Works

Input: Molar concentration for solids/liquids, atmospheric pressure for gases.
Output: Kc for solids/liquids, Kp for gases.

FAQs

What is molarity and its unit?

Molarity is the number of moles of solute per liter of solution. Unit: M (mol/L). Use the molarity calculator.

What is Le Chatelier's principle?

When a reaction is disturbed (temperature, pressure, or concentration), the equilibrium shifts to counteract the change.

What factors affect equilibrium?

Temperature, pressure, and concentration can shift the equilibrium position.

What is the equilibrium state?

Equilibrium occurs when energy and concentrations remain constant over time.

Conclusion

The equilibrium constant calculator quickly computes Kc and Kp, enabling accurate predictions of reaction direction and product formation at equilibrium.

References

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