A large flask is evacuated and weighed, filled with argon gas, and then reweighed. When reweighed, the flask is found to have ga
1 answer:
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Answer:
The answer is 80,1 °C
Explanation:
Let´s start from the mass of the sample and the heat capacities:
First of all, we must calculate an average heat capacity. That's because we have a mixture and it is unknown the heat capacity of the whole sample.
The way we should do this calculation is as follows:
(1)
For example, the mass fraction of Fe is simply:
(2)
If you combine the equations (1) and (2) you have:
(3)
Once calculated the average heat capacity we can solve the problem taking into account the corresponding equation:
(4)
Remember that:
<em>Q:</em> Heat gained or lost
<em>m</em>: Mass of the sample you want to analize
: The value obtained in equation (3)
: Final temperature of the sample
: Initial temperature of the sample
Now we must replace the problem data in equation (4)
Take into account:
- Heat gained in a system have a positive value
- Heat lost in a system have a negative value
- In this problem the sample loses 200 J, for this reason
- The mass of the whole sample is: 10g of Fe + 10g of Ti = 20g of sample
- The temperatures must be in absolute units of temperature (these are: rankine or kelvin)
- The initial temperature of the system is 100°C or 373K
Now we are ready to use equation (4):
(5)
It is clear that the unknown in equation (5) is
The next step is to calculate . Don't forget the signs; these are important.
Key concept: <u>Since the system is loosing heat, the final temperature of the system ( ) should be lower than the initial temperature (
)</u>