Thermal Equilibrium (Simplified) - Online Tutor, Practice Problems & Exam Prep

Thermal equilibrium occurs when two substances at the same temperature no longer exchange thermal energy. Heat transfers from a hotter object to a colder one, resulting in the hotter object losing heat (negative q) and the colder object gaining heat (positive q). The heat lost by the hot object equals the heat gained by the cold object, expressed as $q=mc\Delta T$. Understanding this principle is crucial for thermodynamics and calorimetry applications.

Thermal Equilibrium (Simplified) Concept 1

Thermal equilibrium is when 2 substances in physical contact with one another are at the same temperature. Now we're going to say at the same temperature, these two substances would no longer exchange thermal energy. Now, if we take a look here, we're going to say we're going to initially start out with an object that's at a temperature of 110 degrees Celsius, and I'm going to place it into water at 40 degrees Celsius. So when I do this, there's going to be a heat transfer involved. Always remember that heat moves from a hotter object to a colder object. So by placing the hot cube within the water, we're going to expect the cube to cool off. It's cooling off because it's giving its excess heat to the water. So remember, an object that loses heat has a negative sign for q, and an object that gains heat has a positive sign for q. Water here is gaining the heat of the cube, so it's going to have a positive q.

Eventually, the thermal equilibrium will be reached. At this point, both of them will have the same final temperature. And because of that, we can say that the heat lost by the object is equal to the heat gained by the water. And remember, if your qs or heats are equal to one another, q = mcaT, that means that their mcΔT values are also equal to each other. So cube object negative q object equals the positive q water, and by extension, negative mcΔT of the object equals the positive mcΔT of the water.

Now just realize here that under ideal thermal equilibrium, heat transfers only occur between the solvent and the immersed heated object. We don't have to worry about heat being lost between these 2. Heat is always moving from the hotter object to the colder object. The hotter object is going to have a negative sign for q since it's going to lose its heat. The colder object initially will gain heat, so it's going to have a positive sign for q. So keep this in mind when giving signs for the q of the object versus the q of water or another object.

If 53.2 g Al at 120.0 ºC is placed in 110.0 g H2O at 90 ºC within an insulated container that absorbs a negligible amount of heat, what is the final temperature of the aluminum? The specific heat capacities of water and aluminum are 4.184 J/g ∙ ºC and 0.897 J/g ∙ ºC, respectively.

• A. 75.579 °C
• B. 92.775 °C
• C. 72.975 °C
• D. 57.972 °C

Here’s what students ask on this topic:

What is thermal equilibrium in chemistry?

Thermal equilibrium in chemistry occurs when two substances in physical contact reach the same temperature and no longer exchange thermal energy. This means that the heat lost by the hotter object is equal to the heat gained by the colder object. The principle is crucial for understanding thermodynamics and calorimetry. The equation used to describe this is $q=mc\mathrm{\Delta T}$, where $q$ is the heat transferred, $m$ is the mass, $c$ is the specific heat capacity, and $\mathrm{\Delta T}$ is the change in temperature.

How does heat transfer occur between two objects?

Heat transfer between two objects occurs when they are at different temperatures. Heat always moves from the hotter object to the colder one. This process continues until both objects reach the same temperature, achieving thermal equilibrium. The heat lost by the hotter object (negative $q$) is equal to the heat gained by the colder object (positive $q$). The equation $q=mc\mathrm{\Delta T}$ helps quantify this heat transfer.

What is the significance of the equation q=mcΔT in thermal equilibrium?

The equation $q=mc\mathrm{\Delta T}$ is significant in thermal equilibrium because it quantifies the amount of heat transferred between substances. Here, $q$ represents the heat transferred, $m$ is the mass, $c$ is the specific heat capacity, and $\mathrm{\Delta T}$ is the change in temperature. In thermal equilibrium, the heat lost by the hotter object is equal to the heat gained by the colder object, making this equation essential for calculations in thermodynamics and calorimetry.

Why does heat always move from a hotter object to a colder object?

Heat always moves from a hotter object to a colder object due to the second law of thermodynamics, which states that energy spontaneously spreads from regions of higher temperature to regions of lower temperature. This process continues until thermal equilibrium is reached, meaning both objects are at the same temperature. The heat transfer occurs because the molecules in the hotter object have higher kinetic energy and transfer this energy to the molecules in the colder object through collisions.

What happens to the temperature of two objects when they reach thermal equilibrium?

When two objects reach thermal equilibrium, their temperatures become equal. At this point, no net heat transfer occurs between them because they are at the same temperature. The heat lost by the hotter object is exactly equal to the heat gained by the colder object. This state of balance is crucial for understanding energy transfer in thermodynamics and is described by the equation $q=mc\mathrm{\Delta T}$.