Thermal equilibrium is when two substances in physical contact with one another are at the same temperature. Now we're going to say that at the same temperature, these two substances will 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. Now, eventually, 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 q's or heats are equal to one another, q equals mcat, that means that their mcat values are also equal to each other. So cube object negative cube object equals positive q water, and by extension, negative mcat of the object equals the positive mcat 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 two. 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.
7. Energy, Rate and Equilibrium
Thermal Equilibrium (Simplified)
7. Energy, Rate and Equilibrium
Thermal Equilibrium (Simplified) - Video Tutorials & Practice Problems
Thermal Equilibrium involves two substances that are in physical contact reaching the same final temperature over time.
Thermal Equilibrium Reactions
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concept
Thermal Equilibrium (Simplified) Concept 1
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Video transcript
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example
Thermal Equilibrium (Simplified) Example 1
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Problem
ProblemIf 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
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