Enter the composition of phase A, composition of phase B, and the overall system composition into the calculator to determine the mole fraction of each phase.

Lever Rule Formula

The following formula is used to calculate the mole fraction of each phase in a binary equilibrium phase diagram using the Lever Rule.

Xa = (B – T) / (B – A)Xb = (T – A) / (B – A)Variables:

  • Xa is the mole fraction of phase A
  • Xb is the mole fraction of phase B
  • A is the composition of phase A (in mole fraction or mass fraction)
  • B is the composition of phase B (in mole fraction or mass fraction)
  • T is the overall system composition (in mole fraction or mass fraction)

To calculate the mole fraction of each phase, subtract the overall system composition from the composition of the other phase and divide by the difference in composition between the two phases. This is done for both phases. The sum of the mole fractions of both phases should equal 1, as per the principle of conservation of mass.

What is a Lever Rule?

The Lever Rule is a tool used in thermodynamics to determine the mole fraction (or mass fraction) of each phase of a binary equilibrium phase diagram. It is based on the principle of conservation of mass and is called the “Lever Rule” because it can be visually represented as a lever on a fulcrum, where the lengths of the lever arms are inversely proportional to the amounts of the phases present.

How to Calculate Lever Rule?

The following steps outline how to calculate the Lever Rule:

  1. First, determine the composition of phase A (A) and phase B (B) in mole fraction or mass fraction.
  2. Next, determine the overall system composition (T) in mole fraction or mass fraction.
  3. Next, use the formula Xa = (B – T) / (B – A) to calculate the mole fraction of phase A.
  4. Finally, use the formula Xb = (T – A) / (B – A) to calculate the mole fraction of phase B.

Example Problem:

Use the following variables as an example problem to test your knowledge:

Composition of phase A (A) = 0.4

Composition of phase B (B) = 0.6

Overall system composition (T) = 0.5