Thermal Equilibrium

Definition and Key Concepts

Thermal equilibrium occurs when two substances in physical contact reach the same temperature and no longer exchange thermal energy. This is a fundamental concept in thermodynamics and is essential for understanding heat transfer in chemical and biological systems.

• Thermal energy is transferred from the hotter object to the cooler object until both reach the same temperature.

• At thermal equilibrium, the net heat flow between the substances is zero.

Process of Reaching Thermal Equilibrium

The process can be visualized in three stages:

• Initial States: Two objects at different temperatures (e.g., T1 = 110°C, T2 = 40°C).

• Heat Transfer: Heat moves from the hotter object to the cooler object.

• Final States: Both objects reach the same temperature, and thermal equilibrium is established.

Ideal Thermal Equilibrium

Under ideal thermal equilibrium, heat transfers only occur between the solvent and the immersed heated object, with no loss to the surroundings.

Example Problem

Example: If a 50 g block of lead at 250°C is submerged in a solution at 90°C, the final temperature of the solution will be:

• a) Equal to 90°C

• b) Greater than 90°C

• c) Less than 90°C

Explanation: The final temperature will be greater than 90°C because the hot lead block will transfer heat to the solution, raising its temperature above the initial 90°C.

Application: Calculating Final Temperature

To determine the final temperature when two substances are mixed, use the principle of conservation of energy:

• Heat lost by the hot object = Heat gained by the cold object

The formula for heat transfer is:

• q: heat energy (J)

• m: mass (g)

• c: specific heat capacity (J/g·°C)

• ΔT: change in temperature (°C)

For two substances:

Where:

• Tfinal: final equilibrium temperature

• T1: initial temperature of substance 1

• T2: initial temperature of substance 2

Practice Problem

If 53.2 g of Al at 120.0°C is placed in 110.0 g H2O at 90°C within an insulated container, what is the final temperature? Use the following specific heat capacities:

• Aluminum: 0.897 J/g·°C

• Water: 4.184 J/g·°C

Set up the equation:

Solve for Tfinal to find the equilibrium temperature.

Additional info: The notes focus on the concept of thermal equilibrium, heat transfer, and practical calculation methods, which are central topics in GOB Chemistry.