What is the effect of atmospheric pressure on boiling point?

Atmospheric pressure directly affects the boiling point of a liquid; higher pressure increases the boiling point.

Atmospheric pressure is the force exerted by the weight of the air above us. It's important to understand that this pressure has a direct impact on the boiling point of a liquid. In simple terms, the higher the atmospheric pressure, the higher the boiling point of a liquid. Conversely, the lower the atmospheric pressure, the lower the boiling point.

This is because boiling occurs when the vapour pressure of a liquid equals the atmospheric pressure. Vapour pressure is the pressure exerted by a vapour in equilibrium with its liquid or solid phase. When a liquid is heated, its vapour pressure increases until it equals the atmospheric pressure. At this point, the liquid starts to boil and turns into a gas.

For instance, water boils at 100 degrees Celsius at sea level, where the atmospheric pressure is about 1 atmosphere. However, at higher altitudes, like on a mountain, the atmospheric pressure is lower. This means water will boil at a temperature lower than 100 degrees Celsius. This is why it can take longer to cook food at high altitudes.

On the other hand, if the atmospheric pressure is increased, such as in a pressure cooker, water can remain liquid at temperatures higher than 100 degrees Celsius and food cooks faster. This principle is used in industrial processes and in the kitchen to control the boiling point of liquids.

In conclusion, understanding the relationship between atmospheric pressure and boiling point is crucial in various fields, from cooking to industrial processes. It's a fundamental concept in IGCSE Chemistry and helps us understand how changes in pressure can affect the state of matter.