Help with this thermodynamics and entropy question please

In summary: You can't tell that from what I wrote, but that's clearly what I was thinking about.Nope. I mistakenly meant the ratio of the MC's. You can't tell that from what I wrote, but that's clearly what I was thinking about.In summary, the conversation involves someone trying to solve a physics problem but getting one part wrong and not understanding why. The first question asked for the final temperature and the person got 42.06 Celsius. The second question asked for the total change in entropy and the person is using the equation Q=mcT but is getting different results. They are unsure of where they went wrong and ask for clarification on their process.
  • #1
takelight2
12
1
Homework Statement
A 124.4 g insulated aluminum cup at 18.46 ∘C is filled with 130.0 g of water at 46.91∘C. After a few minutes, equilibrium is reached.

a. Determine the final temperature. (completed)

b. Determine the total change in entropy.
Relevant Equations
Q=mcT
So I've answered the first question and I got a final temp of 42.06 Celsius.

Now for this second one, I don't know why I am getting it wrong:

Im doing 0.215*ln(315.06/291.46) + 1*ln(315.06/319.91)

But it says I am wrong. What about my process is faulty?
 
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  • #2
takelight2 said:
Homework Statement:: A 124.4 g insulated aluminum cup at 18.46 ∘C is filled with 130.0 g of water at 46.91∘C. After a few minutes, equilibrium is reached.

a. Determine the final temperature. (completed)

b. Determine the total change in entropy.
Relevant Equations:: Q=mcT

So I've answered the first question and I got a final temp of 42.06 Celsius.

Now for this second one, I don't know why I am getting it wrong:

Im doing 0.215*ln(315.06/291.46) + 1*ln(315.06/319.91)

But it says I am wrong. What about my process is faulty?
Please fill in the details of how you get the factors 0.215 and 1.
 
  • #3
Also, to be pedantic, if you are working to hundredths of a degree, 0°C is 273.15K, not 273.00, though doubtless it makes very little difference to your answer.
 
  • #4
haruspex said:
Please fill in the details of how you get the factors 0.215 and 1.
Yes, I differ from these values (and more importantly, from their ratio). Instead of the 0.215, I get 112 J/K, and, instead of the 1, I get 544 J/K.
 
  • #6
rude man said:
My numbers agree with @Chestermiller.
(But I don't get the 'ratio' part).
Thanks Rudy. I don't either. I was mistaken about that.
 
  • #7
Chestermiller said:
Thanks Rudy. I don't either. I was mistaken about that.
Actually, I thought you meant the limits of integration which turn out to be ratios after the integration, but separately for the water and the cup.
 
  • #8
rude man said:
Actually, I thought you meant the limits of integration which turn out to be ratios after the integration, but separately for the water and the cup.
Nope. I mistakenly meant the ratio of the MC's.
 

1. What is thermodynamics?

Thermodynamics is the branch of physics that deals with the relationships between heat, work, and energy. It studies how these factors affect the behavior of matter and how they can be used to understand and predict the behavior of physical systems.

2. What is entropy?

Entropy is a measure of the disorder or randomness in a system. In thermodynamics, it is often described as the tendency of a system to move towards a state of equilibrium, where all energy is evenly distributed.

3. How is entropy related to thermodynamics?

In thermodynamics, entropy is a fundamental concept that helps us understand the direction and efficiency of energy transfer and transformation. It is closely related to the second law of thermodynamics, which states that the total entropy of an isolated system always increases over time.

4. How can thermodynamics and entropy be applied in real life?

Thermodynamics and entropy have many practical applications, including in the fields of energy production, climate science, and chemical reactions. For example, understanding entropy can help engineers design more efficient engines and power plants, and it is also used to study the Earth's climate and predict changes in weather patterns.

5. What are some common misconceptions about thermodynamics and entropy?

One common misconception is that entropy only applies to closed systems, when in fact it can also be used to analyze open systems. Another misconception is that entropy can only increase, when in reality it can also decrease in certain situations, such as in living organisms that maintain a high level of order and complexity.

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