K Value Calculator

Calculate a vapor–liquid composition ratio, spring constant, slab thermal conductivity, chemical concentration quotient or first-order decay constant. These different uses of k have different units and assumptions.

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K Value Formula

The following formula is used to calculate a k value.

• Where K is the K value, or vapor-liquid equilibrium ratio.
• y is the mole fraction in the vapor
• x is the mole fraction in the liquid

To calculate this vapor–liquid K value, divide the component’s vapor mole fraction by its positive liquid mole fraction, using equilibrium compositions at the same temperature and pressure. Fractions must lie between 0 and 1. The other calculator modes use F = kx, q = kAΔT/L, the equilibrium concentration quotient, or first-order decay; they do not share this phase-ratio formula.

K Value Definition

In the vapor–liquid context used in the formula above, a component’s K value is its equilibrium vapor mole fraction divided by its equilibrium liquid mole fraction at the same temperature and pressure. This dimensionless composition ratio is not generally identical to a dimensioned Henry-law constant. The same letter also labels unrelated spring, thermal and kinetic quantities. See Penn State’s formulation of the vapor–liquid equilibrium problem.

Can K values be negative?

A vapor–liquid composition ratio cannot be negative because mole fractions cannot be negative; a zero liquid fraction makes y/x undefined. The spring and thermal modes use positive material parameters and magnitudes. The rate mode models nonnegative first-order decay; increasing concentration is outside that model.

K Value Example

FAQ