Calculate Kp for Each of The Following Equilibria

Equilibrium constants (Kp) are fundamental in chemical equilibrium, quantifying the ratio of product to reactant concentrations at equilibrium. This calculator helps you determine Kp values for given equilibria, essential for understanding reaction favorability and predicting product yields.

What is Kp?

The equilibrium constant Kp (for pressure) expresses the ratio of partial pressures of products to reactants at equilibrium. It's particularly useful for gas-phase reactions where concentrations are expressed in terms of partial pressures.

Kp is calculated using the formula:

Kp = (P_C)^c (P_D)^d / (P_A)^a (P_B)^b

Where P represents partial pressures and a, b, c, d are stoichiometric coefficients.

Kp values indicate reaction direction:

Kp > 1: Products favored
Kp = 1: Equal concentrations
Kp < 1: Reactants favored

How to Calculate Kp

To calculate Kp:

Write the balanced chemical equation
Identify the stoichiometric coefficients
Measure or determine the partial pressures of all gases at equilibrium
Apply the Kp formula using these values

Example Reaction

2NO(g) + O2(g) ⇌ 2NO2(g)

At equilibrium, [NO] = 0.1 M, [O2] = 0.2 M, [NO2] = 0.3 M

Kp = (P_NO2)^2 / (P_NO)^2 (P_O2)

Example Calculations

Let's calculate Kp for the reaction:

N2(g) + 3H2(g) ⇌ 2NH3(g)

Partial Pressure (atm)	N2	H2	NH3
Initial	1.0	3.0	0.0
Change	-0.5	-1.5	+1.0
Equilibrium	0.5	1.5	1.0

Calculation:

Kp = (P_NH3)^2 / (P_N2)(P_H2)^3 Kp = (1.0)^2 / (0.5)(1.5)^3 Kp = 1.0 / (0.5 × 3.375) Kp ≈ 0.592

Interpretation of Kp Values

Kp values provide insight into reaction behavior:

Large Kp (>100): Strong product favorability
Small Kp (<0.01): Strong reactant favorability
Kp ≈ 1: Near equilibrium

Temperature affects Kp through the van't Hoff equation:

ln(Kp2/Kp1) = (ΔH°/R)(1/T1 - 1/T2)

FAQ

What units are used for Kp?: Kp is unitless since it's a ratio of pressures.
How does Kp relate to Kc?: Kp and Kc are related through the ideal gas law: Kp = Kc(RT)^Δn
Can Kp be negative?: No, Kp is always positive as it represents a ratio of squares of pressures.
What if a reactant is a solid or liquid?: Solids and liquids have constant activities, so their pressures are not included in Kp calculations.