Question

What is internal energy?

Short answer

Internal energy is the total energy within a system, including both kinetic and potential energies of all particles.

Step-by-step solution

Define Internal Energy

Internal energy is the total energy contained within a thermodynamic system. It includes all microscopic kinetic and potential energies.

Understand Components

Internal energy consists of various components such as the kinetic energy due to the motion of particles, and potential energy from interactions between particles.

Relate to Thermodynamics

In thermodynamics, internal energy is often denoted by the symbol \(U\), and it changes when heat or work is added to or removed from the system.

Use the First Law of Thermodynamics

According to the First Law of Thermodynamics, the change in internal energy \(\Delta U\) of a system is equal to the heat \(Q\) added to the system minus the work \(W\) done by the system: \(\Delta U = Q - W\).

Connect to Everyday Context

In everyday terms, when you heat a system or compress it, its internal energy changes by affecting particle motion and potential energy.

Key concepts

Thermodynamic System

A thermodynamic system is a specific part of the universe that we are interested in studying. Everything outside this system is known as the surroundings. We often examine how energy moves into or out of this well-defined region to understand the system's behavior better.

Thermodynamic systems can be classified in a few different ways, depending on what energies or substances can pass through its boundaries. Common types include:

• Closed System: Only energy, such as heat or work, can cross the boundary, but not matter. An example is a sealed container of gas.
• Open System: Both energy and matter can leave or enter. A boiling pot of water without a lid is a practical example.
• Isolated System: Neither matter nor energy can penetrate the boundary. Examples are very rare in the real world but could include a perfectly insulated container.

By understanding a system's type, we can predict how it might behave or change under different conditions, especially when applying thermodynamic principles.

First Law of Thermodynamics

The First Law of Thermodynamics is all about energy conservation. It tells us that energy cannot be created or destroyed in an isolated system. Instead, it is transformed from one form to another.

Mathematically, this law is expressed as:\[ \Delta U = Q - W \]Here, \( \Delta U \) represents the change in internal energy of a system, \( Q \) is the heat added to the system, and \( W \) is the work done by the system.

In simpler terms, if you add heat to the system (increasing \( Q \)), or if the system does work on its surroundings (increasing \( W \)), the internal energy of the system will change. This fundamental principle helps us understand how systems exchange energy and gives us a way to predict energy changes under various conditions.

Heat and Work Interaction

Heat and work are two primary forms of energy transfer within a thermodynamic system. Understanding their interaction is essential for grasping how internal energy changes occur.

Heat: This is the energy transferred due to temperature difference between a system and its surroundings. When heat is added to a system, it can increase the system's internal energy as the particles move more vigorously.

Work: This refers to the energy transfer that occurs when an external force acts on the system, often changing its volume. Compressions or expansions that move pistons are classic examples.

In thermodynamics, the balance of heat and work interactions influences the system's internal state. For instance, heating a gas inside a piston can do work by pushing the piston upwards. This reduces the available internal energy because part of it is used to perform the work. Understanding how heat and work contribute to energy transformations is vital in fields ranging from engineering to environmental science.