# Variation of vapor pressure with temperature

• utkarshakash
In summary, the conversation discusses the correct way to plot data for a variation of vapor pressure with temperature, with one person suggesting an exponential function and the other mentioning the Clausius-Clapeyron equation. The correct method is determined to be plotting lnP vs 1/T.
utkarshakash
Gold Member

## Homework Statement

The following link shows the variation of vapor pressure with temperature. In which way the data should be plotted to obtain a straight line?

http://www.chem.purdue.edu/gchelp/liquids/vpress.html

## The Attempt at a Solution

For this, I need to know exactly the mathematical relationship which I can't seem to find anywhere. Anyways, my immediate guess would be that the graph is an exponential function. So plotting the graph of lnP vs T would give me a straight line but the correct answer is lnP vs 1/T. I'm sure I'm missing something here.

Are you familiar with the Clausius Clapeyron equation?

Chet

This is the one component, two phase (solid-gas, liquid-gas) "version" of the Clausius-Clayperon equation.

Thanks to both of you.

Can you help?

As a scientist, it is important to understand the underlying principles and equations governing the relationship between vapor pressure and temperature. In this case, the Clausius-Clapeyron equation is the fundamental equation that relates vapor pressure to temperature. This equation is based on the thermodynamic principles of phase equilibrium and can be written as ln(P) = -ΔHvap/R(1/T) + C, where P is vapor pressure, T is temperature, ΔHvap is the enthalpy of vaporization, R is the gas constant, and C is a constant.

Based on this equation, the correct way to plot the data is ln(P) versus 1/T, which would result in a linear relationship. This is because the Clausius-Clapeyron equation is an exponential function, and taking the natural logarithm of both sides results in a linear relationship between ln(P) and 1/T.

Therefore, to obtain a straight line when plotting vapor pressure versus temperature, it is important to use the correct mathematical relationship based on the underlying principles and equations. This ensures accurate and meaningful interpretation of the data.

## 1. How does vapor pressure change with temperature?

The vapor pressure of a substance generally increases with temperature. This is because at higher temperatures, the particles of a substance have more kinetic energy and are more likely to escape into the gas phase, resulting in an increase in vapor pressure.

## 2. Is there a relationship between vapor pressure and temperature?

Yes, there is a direct relationship between vapor pressure and temperature. As temperature increases, so does vapor pressure.

## 3. Why does vapor pressure increase with temperature?

As temperature increases, the average kinetic energy of the particles in a substance increases. This leads to more frequent collisions between particles and an increased likelihood of particles escaping into the gas phase, resulting in an increase in vapor pressure.

## 4. How does the type of substance affect the variation of vapor pressure with temperature?

The type of substance can greatly affect the variation of vapor pressure with temperature. Substances with weaker intermolecular forces, such as gases, will have a larger increase in vapor pressure with temperature compared to substances with stronger intermolecular forces, such as liquids.

## 5. Can vapor pressure decrease with temperature?

In some cases, yes, vapor pressure can decrease with temperature. This is usually observed in substances with very strong intermolecular forces, such as water, where at higher temperatures, more particles can escape into the gas phase resulting in a decrease in vapor pressure.

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