Question

What is evaporation? What is condensation? Which of these processes is endothermic and which is exothermic?

Short answer

Evaporation is the process in which a liquid changes into a gas or vapor, occurring on the surface of a liquid. Condensation is the process by which a gas or vapor changes into a liquid, often when in contact with a cooler surface or when the temperature drops. Evaporation is an endothermic process, as the liquid molecules absorb energy from their surroundings to change into the gas phase. Conversely, condensation is an exothermic process, as gas molecules release energy to their surroundings when changing into the liquid phase.

Step-by-step solution

Definition of Evaporation

Evaporation is the process in which a liquid changes into a gas or vapor, typically due to the liquid molecules gaining enough thermal energy to overcome their intermolecular forces and escape the liquid phase. This usually occurs on the surface of a liquid, such as a puddle of water evaporating into the air.

Definition of Condensation

Condensation is the process by which a gas or vapor changes into a liquid, typically due to the gas molecules losing thermal energy and their intermolecular forces becoming strong enough to hold them in the liquid phase. This often happens when a gas comes into contact with a cooler surface or when the temperature of the gas drops, such as water vapor in the air condensing on a cold window.

Endothermic Process

An endothermic process is a process in which energy (usually in the form of heat) is absorbed from the surroundings. This means the system (in this case, the liquid undergoing evaporation) gains energy, while the surroundings lose energy.

Exothermic Process

An exothermic process is a process in which energy (usually in the form of heat) is released to the surroundings. This means the system (in this case, the gas undergoing condensation) loses energy, while the surroundings gain energy.

Evaporation and Endothermic Process

Evaporation is an endothermic process because the liquid molecules must absorb energy from their surroundings to gain the thermal energy required to overcome their intermolecular forces and change into the gas phase. As a result, energy is taken in by the liquid undergoing evaporation, making it endothermic.

Condensation and Exothermic Process

Condensation is an exothermic process because the gas molecules release energy to their surroundings when they lose thermal energy and change into the liquid phase. As a result, energy is released by the gas undergoing condensation, making it exothermic.

Key concepts

Endothermic Processes

An endothermic process is one in which a system absorbs energy from its surroundings. This energy is typically in the form of heat. Think of it like a sponge soaking up water; the system gains something, while its environment loses it. During these processes:

• Energy is taken in to initiate the process.
• A temperature decrease is often noticed in the surroundings.

Evaporation is a classic example. For a liquid to transform into vapor, it needs to absorb energy. This energy helps the liquid molecules overcome the forces holding them in the liquid state. Ever wondered why you feel cool when getting out of a swimming pool? That's evaporation at work, drawing heat from your skin and leaving you feeling chilly. This endothermic nature makes evaporation crucial for systems like sweating, regulating body temperature.

Exothermic Processes

Exothermic processes are the opposite of endothermic ones. Here, energy is released from a system to its surroundings. Imagine a fireplace; as the wood burns, it releases energy in the form of heat, warming up the room. Characteristics include:

• Energy released, often as heat or light.
• A temperature increase in the surroundings is common.

Condensation is an example. When a gas transforms into a liquid, it releases energy. This is because the molecules release some of their stored energy, allowing them to bind together more closely. Have you ever noticed how your bathroom becomes warm from the steam after a hot shower? That warmth is due to condensation, warming the room as the steam turns back into water. This exothermic release of energy helps in processes like the warming effect of fog on a cold night.

Phase Changes

Phase changes involve the transformation of a substance from one state of matter to another, such as solid to liquid, liquid to gas, or vice versa. Each type of phase change involves energy changes, which can be either endothermic or exothermic.

• Endothermic phase changes: Absorb energy, common in melting and evaporation.
• Exothermic phase changes: Release energy, seen in freezing and condensation.

Understanding these processes helps explain why things behave the way they do under different temperatures and pressures. For instance, when ice melts, it absorbs heat from the surroundings, which is an endothermic process. Conversely, when water vapor condenses on a cold window, it releases heat, which is exothermic. This release or absorption of energy dictates not only everyday experiences, like sweating or seeing dew on grass, but also critical scientific processes and industrial applications.