Question

What occurs when the vapor pressure of a liquid is equal to atmospheric pressure? Explain.

Short answer

When the vapor pressure of a liquid is equal to the atmospheric pressure, the liquid reaches its boiling point. At this point, the liquid's molecules have enough energy to escape into the vapor phase at the same rate that the vapor molecules return to the liquid phase, maintaining an equilibrium state called boiling. During boiling, the liquid turns into a vapor, forming bubbles that rise to the surface and release the vapor into the air, leading to a substantial increase in vapor production and a visible transformation of the liquid into steam or vapor.

Step-by-step solution

Define vapor pressure

Vapor pressure is the pressure exerted by the vapor (or gaseous phase) of a substance in equilibrium with its liquid phase at a given temperature. It measures the tendency of the liquid particles to escape into the air as vapor.

Define atmospheric pressure

Atmospheric pressure is the pressure exerted by the weight of the Earth's atmosphere on the surface of the Earth. It is created by the gravitational force acting on the air molecules above us.

Discuss the implications of their equality

When the vapor pressure of a liquid is equal to the atmospheric pressure, the liquid is at a state where its molecules have enough energy to escape into the vapor phase at the same rate that the vapor molecules return to the liquid phase. This equilibrium state is called "boiling."

Explain boiling

Boiling is the process by which a liquid turns into a vapor as it reaches a specific temperature known as the boiling point. At this temperature, the liquid's vapor pressure becomes equal to the atmospheric pressure, and the liquid begins to vaporize at a higher rate than before. As the liquid converts into vapor, it forms bubbles that rise to the surface and release the vapor into the air. The increased vaporization rate results in a rapid exchange of particles between the two phases, leading to a substantial increase in vapor production and a visible transformation of the liquid into steam or vapor.

Key concepts

Vapor Pressure

Vapor pressure is an essential concept in understanding how liquids evaporate. It's the pressure created by the vapor that forms when a liquid evaporates. This vapor is in balance with the liquid at a specific temperature. Imagine a closed container with water inside; some of the water molecules evaporate to form vapor.
Once the evaporation hits a certain point, the rates of evaporation and condensation become equal. That's the equilibrium, and the pressure at this equilibrium is what we call vapor pressure.

• Vapor pressure varies with temperature: Higher temperatures mean higher vapor pressures.
• It measures how quickly a liquid is converting to vapor.

In practical terms, knowing the vapor pressure helps us anticipate how a liquid behaves when heated.

Atmospheric Pressure

Atmospheric pressure is the pressure exerted by the Earth's atmosphere on everything below it. Think of it as the blanket of air covering the planet, exerting force on all surfaces.
It's influenced by factors like altitude and weather conditions.

• At sea level, the atmospheric pressure is about 101.3 kPa (kilopascals), or 1 atm (atmosphere).
• It decreases as you go higher in altitude because there's less air above you.

The balance between atmospheric and vapor pressure is crucial in determining when a liquid will boil. When vapor pressure equals atmospheric pressure, boiling occurs.

Phase Equilibrium

Phase equilibrium refers to the condition where different phases of a substance coexist in balance, with no net change between them. This is a stable state where the rate at which liquid converts to vapor matches the rate at which vapor returns to liquid.
Imagine a pot of water simmering without the lid: water turns to steam, and steam condenses back to water.

• In phase equilibrium, the appearance of the substance remains constant across phases.
• This equilibrium helps maintain a steady temperature and pressure condition.

Understanding phase equilibrium is vital to grasp how and when a liquid boils, as it involves the transition between liquid and gas.

Vaporization Process

The vaporization process is the transformation of a liquid into vapor. There are two types: evaporation and boiling. Evaporation occurs at temperatures below boiling point, where only the surface molecules gain enough energy to escape.
Boiling, on the other hand, involves the entire liquid reaching a temperature where vapor forms throughout.

• When boiling, bubbles of vapor grow within the liquid.
• The difference between evaporation and boiling lies in the location and energy involved.

Boiling happens when the vapor pressure equals atmospheric pressure. Understanding this helps explain how substances get converted from liquid to gas rapidly under specific conditions.