Thermal Equilibrium - Video Tutorials & Practice Problems
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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
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2m
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Thermal equilibrium is when 2 substances in physical contact with one another are at the same temperature. Now at the same temperature, these two substances would no longer exchange thermal energy by way of the first law of thermodynamics. So if we take a look here, let's say we have this heated metal cube here, and it's initially at a temperature of a 110 degrees Celsius, And we're gonna place it into water at 40 degrees Celsius. Remember, heat transfers. When it comes to heat, it always moves from hotter to colder object. So the cube will be losing some heat. So some of the heat from the cube will be lost and it's gonna go in to the water. So we'd say here that the cube is losing heat, so it would have a negative q, and the water is absorbing that heat, so it'd be a positive q for the water. Eventually though, the q will no longer be able to release any more heat because it'll get to the same temperature as the water. So it's at that moment we've reached thermal equilibrium. Now at thermal equilibrium we can say here that they're both gonna have the same heat. So the negative q of the object, hotter object, object, would be equal to the positive q of water in this case. And if their q's or heats are equal to one another then their m cap formulas are equal to each other, because remember q equals m cap, so negative m cap equals positive m cap. Now under ideal thermal equilibrium heat transfers only occur between the solvent and the immersed heated object. If the situation is not ideal then, then we can say that that additional heat could be absorbed by the calorimeter. So the calorimeter, or the container in this case, same thing, would absorb some of that heat of the object. So here this equation would expand out under non ideal conditions to be negative q of the object equals positive q of the water plus q of the container also known as the calorimeter. So just remember, if your professor is mentioning that this is a pure thermal equilibrium type of question, then you could just say q, negative q hotter object equals positive q of colder object. But if the calorimeter is involved, you have to take into account that it too would absorb some of this heat that's coming off of the hotter object.
Under non-ideal conditions, calorimeter absorbs some of the heat from the object.
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example
Thermal Equilibrium Example 1
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1m
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Here in this example question it says, if 50 gram block of lead at 250 degrees Celsius is submerged in a solution at 90 degrees Celsius, the final temperature of the solution will be so let's just think about it. We have a container, we have a hot piece of lead here being submerged in some colder water. So try to use everyday real experiences here. What happens? I take a hot pan and I dunk it into the sink filled with water. We'll hear the pan sizzle. That's because the pan is releasing its extra heat into the water. The water is becoming vaporized. Remember, at thermal equilibrium they're both gonna reach a a temperature that's the same for both of them. The temperature that they reach should be a temperature somewhere between a 150 degrees Celsius and 90 degrees Celsius because we'd expect the hotter object to release enough heat so that it and the the solvent that it's in can reach the same temperature. So the hotter object cools down some, the colder object warms up some. Their new final temperature will exist somewhere between their two initial temperatures. So we'd expect that the temperature of the solution to be greater than 90 degrees Celsius. It'll be a number between 15090 degrees Celsius.
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Problem
Problem
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.