What is the effect of pressure on a liquid's boiling point?

Verified step by step guidance

1. Understand that the boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure.
2. Recognize that increasing the external pressure on a liquid requires the liquid to reach a higher temperature for its vapor pressure to match the external pressure, thus increasing the boiling point.
3. Conversely, decreasing the external pressure lowers the temperature at which the vapor pressure equals the external pressure, thus decreasing the boiling point.
4. Consider the practical example of water boiling at a lower temperature at higher altitudes due to decreased atmospheric pressure.
5. Remember that this principle is used in pressure cookers, where increased pressure raises the boiling point of water, allowing food to cook faster.

Key Concepts

Boiling Point

The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure surrounding the liquid. At this temperature, the liquid transitions to a gas. For example, water boils at 100°C at standard atmospheric pressure (1 atm), but this temperature changes with variations in pressure.

Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid form at a given temperature. As temperature increases, the vapor pressure of a liquid also increases, leading to a higher likelihood of molecules escaping into the gas phase. This relationship is crucial for understanding how boiling points change with pressure.

Effect of Pressure on Boiling Point

Increasing the external pressure on a liquid raises its boiling point because the liquid must reach a higher temperature for its vapor pressure to match the increased external pressure. Conversely, reducing the pressure lowers the boiling point, which is why water boils at lower temperatures at high altitudes, where atmospheric pressure is lower.