Topic 8.15 min read
Thermal Equilibrium and Thermodynamic Systems
Two systems are in thermal equilibrium when they have the same temperature and no net heat flows between them. Thermodynamics describes a chosen system, its surroundings and the boundary separating them.
Choose Your Level
Beginner Level
A hot body and a cold body exchange heat until both reach the same temperature. At that point they are in thermal equilibrium and there is no net heat flow.
Recommended for Class 11
Thermal Equilibrium and Thermodynamic Systems
Overview
Two systems are in thermal equilibrium when they have the same temperature and no net heat flows between them. Thermodynamics describes a chosen system, its surroundings and the boundary separating them.
Learning Outcomes
- Heat flows spontaneously from higher to lower temperature.
- Equal temperature gives thermal equilibrium and zero net heat flow.
- A diathermic boundary allows heat transfer.
- Open systems exchange mass and energy.
- Closed systems exchange energy but not mass.
- Isolated systems exchange neither mass nor heat.
Intermediate Level
Heat and Temperature
| Quantity | Meaning | SI unit |
|---|---|---|
| Heat | energy transferred because of temperature difference | J |
| Temperature | degree of hotness and measure related to average molecular kinetic energy | K |
Thermal Contact
When bodies at different temperatures are connected through a diathermic substance, heat flows from the hotter body to the colder body until their temperatures become equal.
System, Surroundings and Boundary
| Term | Meaning |
|---|---|
| System | matter or region being studied |
| Surroundings | everything outside the system |
| Boundary | surface separating system and surroundings |
Types of System
| System | Mass exchange | Energy exchange | Example |
|---|---|---|---|
| Open | yes | yes | open beaker |
| Closed | no | yes | sealed container that can be heated |
| Isolated | no | no | ideal thermos flask |
Everyday Example
A hot metal block in cooler water transfers heat to the water. Equilibrium is reached when both have the same temperature, although their internal energies need not be equal.
Common Mistakes
- Use kelvin in gas and molecular-energy equations.
- Distinguish heat, temperature and internal energy.
- Convert all quantities to SI units before calculation.
Short-Question Preparation
Q. Define thermal equilibrium.
A. The state in which systems have the same temperature and no net heat transfer occurs.
Q. What is a diathermic substance?
A. A substance or boundary that allows heat to pass through.
Q. Differentiate open, closed and isolated systems.
A. Open exchanges mass and energy; closed exchanges energy only; isolated exchanges neither.
Sticky Notes
- Heat flows spontaneously from higher to lower temperature.
- Equal temperature gives thermal equilibrium and zero net heat flow.
- A diathermic boundary allows heat transfer.
- Open systems exchange mass and energy.
- Closed systems exchange energy but not mass.
- Isolated systems exchange neither mass nor heat.
60-Second Revision
Two systems are in thermal equilibrium when they have the same temperature and no net heat flows between them. Thermodynamics describes a chosen system, its surroundings and the boundary separating them.
Summary
Two systems are in thermal equilibrium when they have the same temperature and no net heat flows between them. Thermodynamics describes a chosen system, its surroundings and the boundary separating them.
Ask-the-Tutor Modes
- Explain it simply.
- Compare the key terms.
- Solve a numerical.
- Prepare a board-style answer.
- Test me with an MCQ.
Exam Focus
Exam Focus
Important points
- Heat flows spontaneously from higher to lower temperature.
- Equal temperature gives thermal equilibrium and zero net heat flow.
- A diathermic boundary allows heat transfer.
- Open systems exchange mass and energy.
- Closed systems exchange energy but not mass.
- Isolated systems exchange neither mass nor heat.
Common exam traps
- Wrong temperature scale
Long question structure
Definition → explanation → equations → examples.
Common Mistakes
Common Mistakes
- Mistake
Keep heat, temperature and internal energy distinct.
Revision Zone
60-Second Revision
Quick cues from this topic — use them for last-minute revision.
Heat flows spontaneously from higher to lower temperature.
Equal temperature gives thermal equilibrium and zero net heat flow.
A diathermic boundary allows heat transfer.
Open systems exchange mass and energy.
Two systems are in thermal equilibrium when they have the same temperature and no net heat flows between them. Thermodynamics describes a chosen system, its surroundings and the boundary separating them.
- Definition
- Two systems are in thermal equilibrium when they have the same temperature and no net heat flows between them. Thermodynamics describes a chosen system, its surroundings and the boundary separating them.
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Exam Practice
Important Question
Q1. Define thermal equilibrium.
Important Question
Q2. What is a diathermic substance?
Important Question
Q3. Differentiate open, closed and isolated systems.