# Vapor pressure of a liquid homework

• glasshut137
In summary, the conversation discusses the relationship between vapor pressure, pressure, and temperature in determining the state of a liquid. The question is whether a liquid will evaporate, boil, or freeze when the pressure over it is lowered to 190 torr at 25 degrees Celsius, given that its vapor pressure at that temperature is 200 torr. The conclusion is that the liquid will evaporate due to the decrease in vapor pressure and subsequent decrease in pressure holding the liquid together. However, it is noted that this assumes isobaric conditions and does not take into account other factors such as intermolecular forces and boiling point.
glasshut137
[SOLVED] vapor pressure

## Homework Statement

the vapor pressure of a liquid at 25 degrees celcius is 200 torr. If the pressure over the liquid is lowered to 190 torr at 25 degrees celsius the liquid will...

a)evaporate
b)boil
c)freeze

## The Attempt at a Solution

ok, so i think it would evaporate since the vapor pressure would decrease and therefore the decrease in pressure holding the liquid together would allow evaporation to take place. Can someone tell me if my reasoning is correct?

You are close but consider that evaporation is usually applied to liquids under isobaric conditions. What happens to a liquid when you subject it to a slight vacuum (or slightly lower)?

Your reasoning is correct. The vapor pressure of a liquid is the pressure at which its vapor is in equilibrium with its liquid phase at a given temperature. When the external pressure is lowered to 190 torr, it is lower than the vapor pressure of the liquid (200 torr), which means that the vapor molecules have a higher energy and can escape from the liquid surface more easily. This leads to evaporation of the liquid. If the external pressure is further lowered, the liquid may eventually reach its boiling point and start boiling, but in this case, it would simply evaporate. Freezing would not occur as it requires a decrease in temperature, not pressure.

## 1. What is vapor pressure and why is it important?

Vapor pressure is the measure of the tendency of a liquid to escape into the gas phase. It is important because it helps determine the volatility and evaporation rate of a liquid, which can have practical applications in industries such as chemistry, medicine, and food production.

## 2. How is vapor pressure calculated?

Vapor pressure can be calculated using the Clausius-Clapeyron equation, which takes into account the temperature and heat of vaporization of a liquid. However, there are also tables and charts available that provide the vapor pressure of common liquids at different temperatures.

## 3. What factors affect the vapor pressure of a liquid?

The vapor pressure of a liquid is affected by temperature, pressure, and the intermolecular forces between the liquid molecules. Generally, as temperature increases, so does vapor pressure, and as pressure increases, vapor pressure decreases. Stronger intermolecular forces can also lead to lower vapor pressure.

## 4. How does vapor pressure change with altitude?

Vapor pressure decreases with increasing altitude, as atmospheric pressure decreases. This is because there is less pressure pushing down on the liquid, allowing more molecules to escape into the gas phase. This is why liquids tend to evaporate faster at higher altitudes.

## 5. What is the relationship between boiling point and vapor pressure?

Vapor pressure and boiling point are inversely related. As vapor pressure increases, the boiling point decreases and vice versa. This is because at higher vapor pressures, the liquid molecules have a greater tendency to escape into the gas phase, making it easier for the liquid to boil at a lower temperature.

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