Equilibrium Constant Calculator
Equilibrium Constant Calculator computes Kc, Kp, and Q using stoichiometry, activities, and ICE tables, with units, and examples.
Equation Preview
Helping Notes
- Formula (Kc): \(K=\dfrac{[C]^c [D]^d}{[A]^a [B]^b}\). Use equilibrium molarities; omit pure solids/liquids (activity = 1).
- If a coefficient is 0, its concentration term is \([X]^0=1\) and ignored.
- \(K>1\) favors products; \(K<1\) favors reactants; \(K\approx1\) means comparable amounts at equilibrium.
- We use concentrations (Kc) only—like the example page. Temperature affects K but is not an input here.
Results
Equilibrium Constant (K)
Substitutions
Error
Steps
What is Equilibrium Constant Calculator?
An Equilibrium Constant (K) Calculator evaluates the extent of a reversible reaction at a given temperature. For a balanced reaction \(\sum_i \,\nu_i A_i = 0\) (products positive, reactants negative), the thermodynamically correct expression uses activities \(a_i\):
In ideal mixtures, activities are approximated by concentrations or partial pressures, giving \(K_c\) and \(K_p\):
Pure solids and liquids have \(a=1\) and are omitted from \(K\). Comparing \(Q\) with \(K\) predicts direction: if \(Q
About the Equilibrium Constant Calculator
This tool computes \(K_c\), \(K_p\), and \(Q\) from concentrations or partial pressures, checks consistency with stoichiometry, and solves equilibrium compositions with ICE tables. It supports homogeneous and heterogeneous equilibria, lets you toggle ideal/approximate treatments (activities \(\approx\) concentrations/pressures), and converts between \(K_c\) and \(K_p\) using \(\Delta n\). It also reports thermodynamic links (\(\Delta G^{\circ}\)) and flags impossible inputs (negative concentrations, nonphysical pressures, or inconsistent ICE solutions). All formulas are presented in responsive blocks for easy reading on any screen.
How to Use this Equilibrium Constant Calculator
- Enter the balanced reaction with correct stoichiometric coefficients.
- Choose a task: compute \(K_c\) or \(K_p\), compute \(Q\), convert \(K_c\)↔\(K_p\), or solve an ICE table.
- Provide inputs (concentrations in mol/L or partial pressures in bar/atm) and temperature \(T\).
- Click calculate to view the symbolic \(K\)/\(Q\) expression, substitutions, and the numerical result.
- For ICE problems, the tool sets up unknowns, solves for \(x\), and returns equilibrium amounts with validation.
Examples
Example 1: Compute \(K_c\) from equilibrium concentrations
\(\mathrm{H_2(g)+I_2(g)\rightleftharpoons 2HI(g)}\), with \([\mathrm{H_2}]=0.20\,\mathrm{M},\;[\mathrm{I_2}]=0.10\,\mathrm{M},\;[\mathrm{HI}]=0.60\,\mathrm{M}\).
Example 2: Convert \(K_c\) to \(K_p\)
\(\mathrm{N_2(g)+3H_2(g)\rightleftharpoons 2NH_3(g)}\) at \(T=700\,\mathrm{K}\); suppose \(K_c=0.50\). Here \(\Delta n=2-(1+3)=-2\).
Example 3: Heterogeneous equilibrium
\(\mathrm{CaCO_3(s)\rightleftharpoons CaO(s)+CO_2(g)}\).
Example 4: ICE table
\(\mathrm{A\rightleftharpoons 2B}\) with \(K_c=4.00\), initial \([\mathrm{A}]_0=1.00\,\mathrm{M}\), \([\mathrm{B}]_0=0\).
FAQs
What is the difference between \(K_c\) and \(K_p\)?
\(K_c\) uses molar concentrations; \(K_p\) uses partial pressures. For ideal gases, \(K_p=K_c(RT)^{\Delta n}\).
Do solids and pure liquids appear in \(K\)?
No. Their activities are defined as 1, so they are omitted from the expression.
Does a catalyst change \(K\)?
No. It speeds approach to equilibrium but does not alter the equilibrium position or \(K\).
What are the “units” of \(K\)?
Thermodynamically, \(K\) is dimensionless (activities). Apparent units arise when concentrations/pressures are used without normalization.
How do I decide reaction direction?
Compute \(Q\) with current conditions; if \(Q
How does temperature affect \(K\)?
\(K\) is temperature dependent. The van ’t Hoff relation gives \(\ln(K_2/K_1)=-(\Delta H^{\circ}/R)(1/T_2-1/T_1)\).
Can I convert between \(K_c\) and \(K_p\)?
Yes, for ideal gases via \(K_p=K_c(RT)^{\Delta n}\), where \(\Delta n\) is the change in moles of gas.
What if my ICE solution gives negative concentrations?
Inputs are inconsistent with \(K\) or the chosen stoichiometry; recheck initial values and solve the correct root.
Do non‑ideal solutions or gases change \(K\)?
\(K\) is defined with activities. Use activity coefficients or fugacity corrections when deviations from ideality are significant.
Can I get \(K\) from \(\Delta G^{\circ}\)?
Yes: \(\Delta G^{\circ}=-RT\ln K\Rightarrow K=\exp(-\Delta G^{\circ}/RT)\).
How do stoichiometric coefficients affect \(K\)?
They become exponents in the expression; halving a reaction raises \(K\) to the one‑half power, and so on.
Does changing volume affect \(K\)?
\(K\) itself is constant at fixed \(T\); changing volume alters \(Q\) and shifts equilibrium toward restoring \(Q=K\).
Can I use mole fractions instead of pressures?
For ideal gases, \(P_i=y_i P_{\text{tot}}\); inserting into \(K_p\) yields an equivalent expression in mole fractions.