Midterm Q3B


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Emma Li 2C
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Midterm Q3B

Postby Emma Li 2C » Sun Mar 11, 2018 10:36 pm

Could you explain your thought process for 3b, involving comparing the energy efficiencies of the pots?
I thought that aluminum pots would be more energy efficient because their heat capacity values are the smallest!

Thank you!

Joshua Hughes 1L
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Re: Midterm Q3B

Postby Joshua Hughes 1L » Sun Mar 11, 2018 10:41 pm

It would be more efficient to use a copper pot because the specific heat capacity is the lowest of the three (lower than that of iron and aluminum) meaning that it would take less heat to 'heat' up a copper pot and therefore less heat in total to bring the temperature of the water up

Joshua Hughes 1L
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Re: Midterm Q3B

Postby Joshua Hughes 1L » Sun Mar 11, 2018 10:46 pm

Cooper has a Csp of .3846, Aluminum has .9025 and Iron has .4495
So the Specific heat for the different pots is Cu<Fe<Al


Also, you want to use Csp (specific heat) and not Cm(molar heat capacity) because Sp takes into account the grams or weight of the material and the question states for Identical weight pots. Pots that have the same amount of moles of the different substances wouldn't weigh the same and thus the comparison between the pots wouldn't work, we need to compare identical weight pots which could have different densities and different moles of each substance

CameronJohari1J
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Re: Midterm Q3B

Postby CameronJohari1J » Sun Mar 11, 2018 10:47 pm

Because copper has the lowest specific heat capacity, it is the most efficient metal listed for boiling water. Conceptually speaking, copper requires the least amount of joules to raise its temperature per gram. It is important to look at specific heat capacity and not molar heat capacity because aluminum has the lowest molar heat capacity but is not the correct answer as the molar mass of each metal varies.

Scott Chin_1E
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Re: Midterm Q3B

Postby Scott Chin_1E » Sun Mar 11, 2018 10:51 pm

In the case above, would molar mass be considered an extensive property since it's value is dependent upon the metal in question?

Kevin Ru 1D
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Re: Midterm Q3B

Postby Kevin Ru 1D » Sun Mar 11, 2018 10:55 pm

I believe that molar mass would still be considered an intensive property. Since it is still the mass of one mole of a given substance and thus does not depend on the amount of substance.

Pooja Nair 1C
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Re: Midterm Q3B

Postby Pooja Nair 1C » Fri Mar 16, 2018 1:28 am

If the pots are of the same weight, you must compare the specific heat capacities (mass is not a factor if they are all the same weight). The specific heats of iron, copper, and aluminum are 0.4495 J*C*(g^-1), 0.3846 J*C*(g^-1), and 0.9025 J*C*(g^-1) respectively. Since copper has the lowest specific heat capacity, the amount of heat required to heat up the pot will be less than the amount of heat used to heat an aluminum or iron pot to the boiling point of water. (i.e. for pots of 1g, q copper = 29.99 J, q iron = 35.06 J, and q aluminum = 70.40 J)

Rachel Wang
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Re: Midterm Q3B

Postby Rachel Wang » Fri Mar 16, 2018 6:27 pm

Copper pots would be most energy efficient b/c it has the lowest heat capacity constant and thus would heat up faster for an overall lower value of q.


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