Question

When is the energy crossing the boundaries of a closed system heat and when is it work?

Short answer

In the context of energy crossing the boundaries of a closed system, heat refers to the transfer of thermal energy between the system and its surroundings due to a temperature difference, while work refers to the transfer of energy as a result of a force acting over a distance. Heat transfer occurs when there is a temperature difference between the system and its surroundings and can occur through conduction, convection, or radiation. Work transfer occurs when a force is applied to the system, resulting in displacement or the transfer of energy by other means, such as electricity.

Step-by-step solution

Define Closed System

A closed system is a physical system that does not exchange matter with its surroundings, but can exchange energy in the form of heat and work. In other words, no mass enters or leaves the system, but energy can be transferred across its boundary.

Define Heat

Heat is the transfer of thermal energy between a system and its surroundings due to a temperature difference. It can flow from the system to its surroundings or vice versa as a result of a temperature difference. Heat is often denoted by \(Q\), and is measured in units of joules (J).

Define Work

Work is the transfer of energy between a system and its surroundings as a result of a force acting over a distance. Like heat, work is also measured in joules (J) and is often denoted by \(W\).

Heat Transfer in a Closed System

The energy crosses the boundaries of a closed system as heat when there is a temperature difference between the system and its surroundings. In this case, heat will flow from the higher temperature region to the lower temperature region. Examples of heat transfer in a closed system include: 1. Conduction: Heat transfer through a solid material, such as a metal rod, due to a temperature difference along the material. 2. Convection: Heat transfer between a fluid (like air or water) and a solid boundary, driven by temperature differences and the movement of the fluid. 3. Radiation: Heat transfer through electromagnetic waves, such as the heat from the Sun reaching Earth's surface.

Work Transfer in a Closed System

The energy crosses the boundaries of a closed system as work when a force is applied to the system and results in a displacement. Examples of work transfer in a closed system include: 1. Mechanical work: When a piston moves within a closed chamber (like in an engine), the change in the volume of the chamber causes work to be done. 2. Electrical work: When electrical energy is transferred between a system and its surroundings, like a charged capacitor discharging through a resistor, this is also considered work. In summary, energy crosses the boundaries of a closed system as heat when there is a temperature difference between the system and its surroundings, and as work when a force is applied to the system resulting in the displacement of a boundary or the transfer of energy by other means, such as electricity.