Question

Which processes are endothermic? (a) Condensation (b) Melting (c) Evaporation (d) Sublimation (e) Deposition (f) Freezing

Short answer

Endothermic processes are melting, evaporation, and sublimation.

Step-by-step solution

Understanding Endothermic Processes

An endothermic process absorbs heat from the surroundings. In these processes, substances typically move from a lower energy state to a higher energy state, which requires the input of energy.

Analyzing Each Process

Let's analyze each process: (a) Condensation - Change from gas to liquid: Exothermic, as it releases heat. (b) Melting - Change from solid to liquid: Endothermic, as it requires heat absorption. (c) Evaporation - Change from liquid to gas: Endothermic, as it requires heat absorption. (d) Sublimation - Change from solid to gas: Endothermic, as it requires heat absorption. (e) Deposition - Change from gas to solid: Exothermic, as it releases heat. (f) Freezing - Change from liquid to solid: Exothermic, as it releases heat.

Identify Endothermic Processes

From the analysis, the processes that require energy absorption (endothermic) are: - Melting: Solid to liquid - Evaporation: Liquid to gas - Sublimation: Solid to gas

Key concepts

Thermodynamics

Thermodynamics is the branch of physical science that deals with the relations between heat and other forms of energy. It describes how thermal energy is converted to and from other forms of energy and how it affects matter. A key aspect of thermodynamics is understanding how heat can be absorbed or released in various processes.

When we talk about endothermic processes, we're talking about instances where a system absorbs heat from its surroundings. In these scenarios, heat uptake usually results in a change of state or phase of the substance. This heat absorption is essential for the substance to achieve a higher energy state.

The First Law of Thermodynamics, which is essentially the law of energy conservation, states that energy cannot be created or destroyed in an isolated system. This principle helps us understand why certain processes absorb energy and others release it.

Phase Transitions

Phase transitions refer to the changes between different states of matter: solid, liquid, and gas. These changes require either the absorption or release of energy in the form of heat.

• Melting: This is the transformation from a solid to a liquid. Melting is an endothermic process because it requires the addition of heat to break the bonds holding the solid structure together.
• Evaporation: In this phase change, a liquid turns into a gas. It's another endothermic process as it needs heat to allow liquid molecules to overcome intermolecular forces and disperse into the air as vapor.
• Sublimation: Sublimation occurs when a solid changes directly into a gas, skipping the liquid stage. It requires even more energy than melting and evaporation because it directly breaks the bonds of a solid to become a gaseous state.

These processes are crucial to our understanding of how matter behaves and changes under different thermal conditions.

Heat Absorption

Heat absorption is a fundamental concept in understanding how endothermic processes work. In simple terms, it's the uptake of thermal energy by a system from its surroundings. This uptake of energy can cause various chemical or physical changes.

In endothermic reactions, heat absorption results in a positive change in enthalpy. This means the system gains energy.

• Melting requires absorbing heat to transition from a solid to a liquid state.
• Evaporation demands the intake of heat for a liquid to become a gas.
• Sublimation needs substantial heat absorption to allow a solid to directly form a gas.

Without sufficient heat, these transitions would not occur, illustrating the crucial role of energy intake in enabling phase changes. Understanding how heat is absorbed gives insight into why and how substances alter their states of matter.