# Vapour Pressure at Dew Point

• cruckshank
In summary, the conversation is about using Dalton's/Raoult's Law to determine the vapor pressure of a solution of equimolar benzene and toluene. The vapor pressures of pure toluene and pure benzene at 20 C are 2.933kPa and 9.866kPa, respectively. When only a few droplets of liquid remain, the remaining species is benzene.

#### cruckshank

THERE IS NO TEMPLATE BECAUSE GHIS HOMEWORK WAS PLACED IN AN INCORRECT FORUM

Equimolar benzene and and toluene form essentially ideal solutions. At 20degC the vapour of benzene and toluene are 9.866kPa and 2.933kPa respectively. The solution is boiled by reducing the external pressure below the vapour pressure.

What is the vapour pressure when only a few droplets of liquid remain? Assume still at 20degC.

I know I need to use Dalton's/Raoult's Law, but can't work out how to start really. Help would be appreciated, thanks.

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From your problem statement info, what are the vapor pressures of pure toluene and pure benzene at 20 C?

When most of the liquid has boiled away, which of the two species remains?

## 1. What is vapour pressure at dew point?

Vapour pressure at dew point refers to the amount of pressure exerted by water vapor in the air when it reaches the temperature at which it turns into liquid. This is known as the dew point temperature and is the point at which the air is fully saturated with water vapor.

## 2. How is vapour pressure at dew point calculated?

Vapour pressure at dew point can be calculated using the Magnus formula, which takes into account the air temperature and relative humidity. The formula is: Pd = 6.112 x e^(17.67T / (T + 243.5)), where Pd is the vapour pressure at dew point in kilopascals and T is the air temperature in degrees Celsius.

## 3. What factors affect vapour pressure at dew point?

The main factors that affect vapour pressure at dew point are air temperature, relative humidity, and air pressure. Warmer temperatures can hold more water vapor, while high relative humidity means the air is close to its saturation point. Changes in air pressure can also affect the dew point temperature.

## 4. Why is vapour pressure at dew point important?

Vapour pressure at dew point is important for weather forecasting, as it can indicate the likelihood of precipitation. It is also used in industrial processes, such as in the production of pharmaceuticals and in food processing, to control the humidity levels and prevent moisture-related issues.

## 5. How does vapour pressure at dew point relate to relative humidity?

Vapour pressure at dew point and relative humidity are closely related. At the dew point temperature, the relative humidity is 100%, meaning the air is fully saturated with water vapor. As the air temperature decreases, the relative humidity increases, and when it reaches 100%, the dew point temperature is reached and condensation occurs.