Enter all but one of the vapor pressures at temperature, enthalpy of vaporization, ideal gas constant, initial temperature, and final temperature into the calculator to determine the missing variable.

## Clausius Clapeyron Equation Formula

The Clausius-Clapeyron equation is used to calculate the vapor pressure of a substance at different temperatures. The equation is as follows:

ln(P2/P1) = (ΔHvap/R) * (1/T1 - 1/T2)

Variables:

- P1 is the vapor pressure at temperature T1
- P2 is the vapor pressure at temperature T2
- ΔHvap is the enthalpy of vaporization
- R is the ideal gas constant (8.314 J/(mol·K))
- T1 is the initial temperature
- T2 is the final temperature

To calculate the vapor pressure at a different temperature, take the natural logarithm of the ratio of the vapor pressures at the two temperatures. Multiply the enthalpy of vaporization by the reciprocal of the ideal gas constant, and then multiply that by the difference in the reciprocals of the initial and final temperatures.

## What is a Clausius Clapeyron Equation?

The Clausius-Clapeyron equation is a mathematical relationship that describes the phase transition between two states of matter, such as the transition from liquid to gas during evaporation. It was developed by physicists Rudolf Clausius and Benoît Paul Émile Clapeyron in the 19th century. The equation provides a quantitative way of understanding how the pressure at which this phase transition occurs depends on the temperature. It is derived from the principles of thermodynamics and assumes that the transition between phases is an equilibrium process. The equation is ln(P2/P1) = -ΔHvap/R(1/T2 – 1/T1), where P1 and P2 are the pressures at temperatures T1 and T2, ΔHvap is the enthalpy of vaporization, and R is the ideal gas constant. This equation is particularly useful in meteorology and physical chemistry for calculating the saturation vapor pressure of water or other liquids.

## How to Calculate Clausius Clapeyron Equation?

The following steps outline how to calculate the Clausius Clapeyron Equation:

- First, determine the vapor pressure of the substance at one temperature (P1) and its corresponding temperature (T1).
- Next, determine the vapor pressure of the substance at a different temperature (P2) and its corresponding temperature (T2).
- Next, calculate the difference in temperature (ΔT = T2 – T1) and the difference in vapor pressure (ΔP = P2 – P1).
- Finally, use the Clausius Clapeyron Equation: ln(P2/P1) = -ΔHvap/R * (1/T2 – 1/T1), where ΔHvap is the enthalpy of vaporization and R is the gas constant.
- After inserting the values and calculating the result, check your answer with the calculator above.

**Example Problem:**

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

Vapor pressure at T1 (P1) = 2.5 atm

Temperature at T1 (T1) = 300 K

Vapor pressure at T2 (P2) = 4.2 atm

Temperature at T2 (T2) = 350 K