What is equilibrium constant?

The equilibrium constant is a numerical value that indicates the extent to which a reversible reaction reaches equilibrium. In simple words, if a reaction can go in both directions (forward and backward), then the equilibrium constant helps to understand whether more products or reactants are formed at the equilibrium state.

The equilibrium constant can be expressed in two common forms:

• Kc — in terms of concentration (mol L⁻¹)
• Kp — in terms of pressure (atm)

Both these values ​​depend on the nature and temperature of the reaction.

How to use the calculator?

• Write the reaction (optional, just for display).
• Add the reactants and products along with their coefficients.
• Enter the concentration (M) or partial pressure (atm) of each species.
• Select from the drop down – Kc, Kp, or Convert.
• Enter the temperature and R (gas constant) values ​​if you want to convert.
• Press the Compute button – and you will get the result immediately.

Relation between K_c and K_p

The equilibrium constants K_c (concentration-based) and K_p (pressure-based) are related by the formula:

K_p = K_c × (RT)^Δn

Where:

• Δn = (moles of gaseous products) − (moles of gaseous reactants)
• R = 0.0821 L·atm·mol⁻¹·K⁻¹ (gas constant)
• T = temperature in Kelvin (K)

If Δn = 0, then (R · T)^Δn = 1 and therefore K_p = K_c.

Frequently Asked Questions (FAQs)

Q1. What does the equilibrium constant mean?
The equilibrium constant tells us in which direction the reaction has proceeded more — toward the products or toward the reactants.

Q2. Does changing temperature affect Kc or Kp?
Yes, the equilibrium constant depends only on temperature. It changes if the temperature of the system changes.

Q3. When are Kc and Kp equal?
Kc and Kp are equal when the change in the number of gaseous moles (Δn) is zero.
K_c = K_p

Q4. What are the units of Kc and Kp?
The units of Kc and Kp depend on the overall reaction. If the total power (Δn) is zero, the equilibrium constant becomes unitless.