First law of thermodynamics

Definition

The first law of thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. This fundamental principle underlines the concept that the total energy of an isolated system is constant, emphasizing the relationship between heat transfer, work, and internal energy in physical processes.

5 Must Know Facts For Your Next Test

1. The first law can be mathematically expressed as \( \Delta U = Q - W \), where \( \Delta U \) is the change in internal energy, \( Q \) is the heat added to the system, and \( W \) is the work done by the system.
2. This law implies that if a system absorbs heat and does work on its surroundings, its internal energy will decrease.
3. The first law of thermodynamics is often referred to as the principle of conservation of energy, highlighting that all energy transformations must account for energy entering and leaving the system.
4. In closed systems, any increase in internal energy results from heat added to the system minus work done by the system on its environment.
5. Real-world applications of this law can be seen in engines, refrigerators, and heat pumps, where energy conversions occur regularly.

Review Questions

• How does the first law of thermodynamics apply to real-world systems like engines?
  • In engines, the first law of thermodynamics explains how fuel energy is converted into work and heat. When fuel combusts, it releases heat, which increases the internal energy of the gas inside the engine cylinders. This increase in internal energy does work on the pistons to generate motion. Therefore, energy is transformed rather than created or destroyed, illustrating the first law in action.
• Evaluate how heat transfer affects internal energy in a closed system according to the first law of thermodynamics.
  • In a closed system, any heat transfer into the system will increase its internal energy, while heat transfer out will decrease it. According to the first law, this change in internal energy can be quantified by accounting for work done by or on the system. For example, if a closed container of gas absorbs heat while expanding against a piston, it must do work on that piston. The balance of these factors shows how crucial heat transfer is for determining changes in internal energy.
• Assess the implications of the first law of thermodynamics on designing more efficient thermal systems.
  • Understanding the first law helps engineers design thermal systems with higher efficiency by minimizing energy losses during transformations. By analyzing where energy is converted to waste heat or where work can be maximized from input energy, designers can implement insulation and optimize processes. This knowledge not only leads to better performance but also supports sustainability efforts by reducing overall energy consumption in applications such as heating and cooling systems.

Related terms

Internal Energy: The total energy contained within a system, encompassing both kinetic and potential energy of the particles making up the system.

Heat Transfer: The movement of thermal energy from one object or system to another due to a temperature difference.

Work: The process of energy transfer that occurs when a force is applied over a distance, resulting in the displacement of an object.