11.4 - HEAT, INTERNAL ENERGY AND WORK
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Understanding Heat and Temperature
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Today, we're discussing the concept of heat – the energy that flows due to a temperature difference. Can anyone tell me how heat flows between two bodies?
I think heat moves from hot to cold objects!
Exactly! Heat flows from a region of higher temperature to one of lower temperature until thermal equilibrium is achieved. This is a fundamental principle in thermodynamics.
What does thermal equilibrium mean?
Great question! Thermal equilibrium is reached when two objects have the same temperature, and there's no net flow of heat between them.
So if I touch a cold metal, it feels cold because heat is flowing from my hand into the metal?
Correct! This interaction illustrates how heat transfer occurs; a good way to remember this is 'Hot flows to Cold.'
Got it! What about internal energy?
Internal energy, represented by U, is the total energy associated with the system's molecules. It's the sum of their kinetic and potential energies. Internal energy is only dependent on the system's current state, not how it got there, which makes it a crucial state variable.
To summarize today, remember that heat moves from hot to cold, achieving thermal equilibrium, and internal energy is about the energy contained within a system.
Internal Energy in Depth
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Let’s explore more about internal energy. Why do we care about it in thermodynamics?
Is it because it helps us understand how energy changes within a system?
Absolutely! Internal energy helps us quantify how energy stores change in a system. Can anyone remind me what state variables are?
They are properties that only depend on the state of the system and not on how it got there.
Correct! Internal energy is a state variable. In contrast, heat and work are modes of energy transfer and not state variables. Now, could someone explain the difference between internal energy and heat?
Internal energy is the energy stored in the system, while heat is energy in transit.
Perfect! Internal energy changes when you add heat or do work on the system. To wrap up, always remember: internal energy depends on the state and is about what energy is stored, while heat is what gets transferred.
Work and The First Law of Thermodynamics
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Today we’re introducing work in thermodynamics. Does anyone know how work relates to a thermodynamic system?
Is it the energy transferred when a force is applied?
Exactly! Work can be done by a gas expanding against a piston. Now, who can tell me how work and heat relate to internal energy?
Isn't there a principle that relates them called the First Law of Thermodynamics?
Yes! The First Law states that ΔQ = ΔU + ΔW. This means the heat added to a system equals the change in internal energy plus the work done by the system.
So if I put heat in a system, it can either increase internal energy or do work on the surroundings?
Exactly right! And that leads to understanding energy conservation in thermodynamics. Always remember the triangle of relationships between heat, work, and internal energy.
In summary, the First Law connects heat, internal energy, and work in a beautifully coherent principle about energy conservation in thermodynamic systems.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The section provides a comprehensive examination of the relationship between heat, internal energy, and work, detailing how these concepts interact in thermodynamic processes. It highlights the non-dependence of internal energy on the path taken to achieve a given state and emphasizes the distinction between heat as energy in transit and internal energy as a state variable.
Detailed
Heat, Internal Energy, and Work
The interrelationship between heat, internal energy, and work is fundamental in understanding thermodynamic processes. Here’s a deeper dive into these concepts:
- Heat Transfer: Heat is typically defined as energy in transit caused by a temperature difference between physical systems. When two bodies at different temperatures are in contact, heat flows from the body at a higher temperature to the one at a lower temperature until thermal equilibrium is achieved.
- Internal Energy (U): Internal energy is the total energy associated with the microscopic constituents of a system, comprising both kinetic and potential energy at the molecular level. Unlike kinetic energy which is associated with the motion of the entire system, internal energy focuses solely on the random microscopic motions of the system's particles. Importantly, internal energy is a state variable, meaning it only depends on the system's current state (specific values of pressure, volume, and temperature) and is independent of how that state was reached.
- Work (W): Work is the energy transferred to or from a system through mechanical means (such as moving parts) rather than through heat. In thermodynamics, work done by a gas expanding in a piston, for example, directly influences its internal energy.
- Energy Change: The internal energy of a system can change through the two modes of energy transfer: heat and work. The First Law of Thermodynamics is articulated as:
ΔQ = ΔU + ΔW
where ΔQ is the heat added to the system, ΔU the change in internal energy, and ΔW the work done by the system. This fundamentally illustrates the conservation of energy principle within thermodynamics.
- Memory Aids: To aid memorization, remember that heat always flows from hot to cold (think of the mnemonic 'Hot flows to Cold') and that internal energy signifies energy within the system (you can think of it as 'the internal bank of energy').
In summary, each key concept plays a crucial role in understanding how energy interacts within thermodynamic systems, leading to processes that drive engines, refrigerators, and various scientific principles.
Youtube Videos
Key Concepts
-
Heat: Energy in transit due to temperature differences.
-
Internal Energy: Total energy associated with a system's molecules.
-
Work: Energy transfer due to mechanical action.
-
Thermal Equilibrium: Condition when two bodies reach equal temperature.
-
First Law: Conservation principle connecting heat, work, and internal energy.
Examples & Applications
An ice cube melting on a hot surface: Heat flows from the surface to the cube, increasing the cube's internal energy until it melts.
Pushing a piston down in a cylinder compressing gas: Work is done on the gas, increasing its internal energy.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
When heat does flow, hot to cold it goes!
Acronyms
H-U-W
Heat flows (H)
Internal energy (U)
Work done (W).
Stories
Imagine a water heater: it heats water (internal energy rises) as long as the heat from the heater flows into the water until both reach the same temperature.
Memory Tools
Use 'H-U-W' to remember: Heat, Internal energy, Work.
Flash Cards
Glossary
- Heat
Energy transferred from one system to another due to a temperature difference.
- Internal Energy (U)
The total energy associated with the microscopic constituents of a system, including kinetic and potential energies.
- Work (W)
Energy transferred to or from a system by mechanical means, influencing the internal energy.
- Thermal Equilibrium
A state reached when two bodies in contact with each other have the same temperature, leading to no net heat flow.
- First Law of Thermodynamics
The principle that states the total energy of a closed system is constant; energy can neither be created nor destroyed, only transformed.
- State Variable
A property that depends only on the state of a system and not on how the state was achieved.
Reference links
Supplementary resources to enhance your learning experience.