## Winter 2013 Midterm Q2A

Chin_Alyssa_3I
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### Winter 2013 Midterm Q2A

Q: Your very particular friend Sheldon asks for a glass of exactly 400g of water at 16 C. You can get liquid water at room temperature from the faucet and ice at 0C from the freezer. How many grams of ice and how many grams of water must you combine to make Sheldon's very specific water?

The only part I don't understand is why we need to multiple the moles with the enthalpy of fusion and add it to mCsp(delta)T to find q(ice). And why for q(water) it's only mCsp(delta)T.

Chem_Mod
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### Re: Winter 2013 Midterm Q2A

The only reason I can think of that would explain why you need to multiply the Csp of ice by the number of moles of ice is if the Csp of ice does NOT contain inverse moles in its units. Whenever you're working with these types of problems, just double check the units of your specific heat(s) so you know what you have to/don't have to multiply

Patrick_Mac_3D
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### Re: Winter 2013 Midterm Q2A

Q2C
I can do this problem mathematically, but I'm sure there is a much simpler way to do the problem. Any thoughts?

Patrick_Mac_3D
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### Re: Winter 2013 Midterm Q2A

Nevermind.

Coco Hailey 2E
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### Re: Winter 2013 Midterm Q2A

I still don't understand where the equation q(ice) = n*∆H + m*C_sp * ∆T comes from?? Also what is C_sp?

Hector_Gutierrez 1J
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### Re: Winter 2013 Midterm Q2A

I am also having a difficult time trying to figure out how one would derive the equation to solve the problem?

ntruong2H
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### Re: Winter 2013 Midterm Q2A

Coco Hailey 2E wrote:I still don't understand where the equation q(ice) = n*∆H + m*C_sp * ∆T comes from?? Also what is C_sp?

The equation for ice breaks down as follows:

The n*∆H part is where we first have to melt the ice. n is the amount of moles of ice times ∆H, the molar heat of fusion (fusion is the process of going from a solid to a liquid, i.e. melting).

The m*C_sp * ∆T part accounts for the heating of the ice from its melting point of 0 degrees Celsius to the desired temperature of 16 degrees C. m is the mass in grams, C_sp is the specific heat capacity, and delta T is the temperature difference.

The reason we must add these two equations is because to get to liquid water at 16 degrees Celsius, the ice must be melted first and then heated. Hope this helps!

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### Re: Winter 2013 Midterm Q2A

For part C why should we add less ice ?

Minu Reddy
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### Re: Winter 2013 Midterm Q2A

The reason you add less ice is because the orange juice has a lower heat capacity and therefore does not need as much heat to be cooled.

Eman_Burney_1D
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### Re: Winter 2013 Midterm Q2A

Correct me if I am wrong, but I think if an object has a lower heat capacity, that means it cools and heats up faster, versus an object that has a higher heat capacity would heat and cool slower. So water, with the higher heat capacity, would require more ice because it cools slower than orange juice would. (This is a response to Q2 Part C.)

emilyharland
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### Re: Winter 2013 Midterm Q2A

On part A, how would we determine that the q of the water is the one that is negative in the equation qice=-qwater?