Kp Calculator

In chemistry, Kc and Kp are equilibrium constants expressed in terms of concentration and partial pressure — and the Kp Calculator converts between them for any gas-phase reaction. Select whether you want to convert Kc to Kp or Kp to Kc, then enter your Kc or Kp value, temperature (K), Δn (change in moles of gas), and pressure unit to get the converted equilibrium constant. Secondary outputs include the RT factor and the formula used in the calculation.

Equilibrium constant in terms of concentration

Equilibrium constant in terms of partial pressure

K

Temperature in Kelvin

Difference between moles of gaseous products and reactants

Results

Calculated Value

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RT Factor

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Formula Used

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Frequently Asked Questions

What is Kp, and how is it different from Kc?

Kp is the equilibrium constant expressed in terms of partial pressures of gases, while Kc uses molar concentrations. Kp only considers gaseous species, whereas Kc includes all species in solution. Both constants describe the same equilibrium but use different units and expressions.

How do you calculate Kp from Kc?

Use the formula Kp = Kc(RT)^Δn, where R is the gas constant (0.08314 L·atm/mol·K), T is temperature in Kelvin, and Δn is the difference between moles of gaseous products and reactants. This conversion accounts for the difference between concentration and pressure units.

What is Δn and how do I calculate it?

Δn represents the change in the number of moles of gas during the reaction. Calculate it as (moles of gaseous products) - (moles of gaseous reactants). Only count gases in this calculation; solids and liquids are excluded.

When is Kp equal to Kc?

Kp equals Kc when Δn = 0, meaning there's no change in the number of moles of gas during the reaction. In this case, the RT factor becomes 1, and both equilibrium constants have the same numerical value regardless of temperature.

Can I use different pressure units for Kp calculations?

Yes, you can use various pressure units like atm, kPa, bar, Torr, or mmHg. However, the gas constant R value must match your chosen pressure unit. For atm, use R = 0.08314 L·atm/mol·K.

Why is temperature important in Kp and Kc conversions?

Temperature affects the relationship between pressure and concentration through the ideal gas law. The RT term in the conversion formula accounts for this relationship, making temperature essential for accurate conversions between Kp and Kc.

What happens if Δn is negative?

When Δn is negative, there are fewer moles of gaseous products than reactants. This makes (RT)^Δn less than 1, so Kp will be smaller than Kc. The conversion formula still applies normally with the negative exponent.