Work done on/by the system

Definition

Work done on/by the system refers to the energy transfer that occurs when a force is applied to a system, causing it to move or change its state. In thermodynamics, this concept is crucial because it connects mechanical energy to thermal energy, illustrating how energy can be transformed and conserved within a closed system. Understanding this concept allows for a clearer interpretation of how systems interact with their surroundings, particularly in terms of energy changes that occur during processes like expansion and compression.

5 Must Know Facts For Your Next Test

1. Work can be positive or negative: positive work is done on the system when energy is added, while negative work is done by the system when it expends energy on its surroundings.
2. The work done on/by the system can be calculated using the formula $$W = F imes d$$, where $$F$$ is the force applied and $$d$$ is the distance moved in the direction of the force.
3. In a closed system, the first law of thermodynamics states that any change in internal energy is equal to heat added to the system minus work done by the system.
4. Work done on/by the system is significant during phase changes; for instance, when ice melts into water, work is involved in overcoming intermolecular forces.
5. Understanding work in thermodynamic processes helps in analyzing cycles such as those found in engines and refrigerators, which rely on work for efficient energy conversion.

Review Questions

• How does work done on/by the system affect the internal energy of a closed system?
  • The work done on/by the system directly influences its internal energy according to the first law of thermodynamics. When work is done on the system (positive work), it increases the internal energy, leading to potential changes in temperature or phase. Conversely, when work is done by the system (negative work), it decreases internal energy. This relationship highlights how mechanical processes are intertwined with thermal changes.
• Analyze how the concept of work done impacts real-world applications like engines and refrigerators.
  • In engines, work done on/by the system is crucial for converting thermal energy into mechanical work. For instance, in an internal combustion engine, fuel combustion generates heat that increases gas pressure, performing work on moving pistons. Similarly, refrigerators utilize work to transfer heat from a cooler space to a warmer one. Understanding how work is applied and conserved allows engineers to design more efficient machines that optimize energy use.
• Evaluate different scenarios where work done on/by the system results in significant changes in state or energy transformations.
  • Consider a gas contained within a piston-cylinder assembly. When external pressure decreases and allows gas expansion (work done by the system), it can lead to a temperature drop as internal energy decreases. Alternatively, if external pressure increases and compresses the gas (work done on the system), it can raise temperature as internal energy increases. These scenarios illustrate how mechanical work directly influences thermal conditions and phase changes within a system, emphasizing its importance in thermodynamic processes.

Related terms

System: A defined quantity of matter or region in space chosen for analysis in thermodynamics, which can exchange energy and matter with its surroundings.

Heat Transfer: The movement of thermal energy from one body or system to another due to temperature differences, often occurring alongside work done on/by the system.

First Law of Thermodynamics: A principle stating that energy cannot be created or destroyed, only transformed; it establishes the relationship between internal energy, heat added to the system, and work done.