Winter 2013 Midterm Q2A

Moderators: Chem_Mod, Chem_Admin

Chin_Alyssa_3I
Posts: 34
Joined: Fri Jul 22, 2016 3:00 am

Winter 2013 Midterm Q2A

Postby Chin_Alyssa_3I » Tue Feb 07, 2017 9:15 pm

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
Posts: 18400
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 435 times

Re: Winter 2013 Midterm Q2A

Postby Chem_Mod » Tue Feb 07, 2017 11:31 pm

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
Posts: 12
Joined: Wed Sep 21, 2016 2:58 pm

Re: Winter 2013 Midterm Q2A

Postby Patrick_Mac_3D » Wed Feb 08, 2017 7:57 pm

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
Posts: 12
Joined: Wed Sep 21, 2016 2:58 pm

Re: Winter 2013 Midterm Q2A

Postby Patrick_Mac_3D » Wed Feb 08, 2017 8:04 pm

Nevermind.

Coco Hailey 2E
Posts: 32
Joined: Fri Sep 25, 2015 3:00 am

Re: Winter 2013 Midterm Q2A

Postby Coco Hailey 2E » Sun Feb 12, 2017 7:04 pm

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
Posts: 23
Joined: Wed Sep 21, 2016 2:58 pm

Re: Winter 2013 Midterm Q2A

Postby Hector_Gutierrez 1J » Sun Feb 12, 2017 9:41 pm

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

ntruong2H
Posts: 50
Joined: Sat Jul 09, 2016 3:00 am
Been upvoted: 1 time

Re: Winter 2013 Midterm Q2A

Postby ntruong2H » Sun Feb 12, 2017 10:39 pm

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!

Madeline_Foo_3J
Posts: 26
Joined: Wed Sep 21, 2016 3:00 pm

Re: Winter 2013 Midterm Q2A

Postby Madeline_Foo_3J » Mon Feb 13, 2017 8:56 pm

For part C why should we add less ice ?

Minu Reddy
Posts: 31
Joined: Sat Jul 09, 2016 3:00 am

Re: Winter 2013 Midterm Q2A

Postby Minu Reddy » Mon Feb 13, 2017 9:03 pm

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
Posts: 15
Joined: Wed Sep 21, 2016 2:57 pm

Re: Winter 2013 Midterm Q2A

Postby Eman_Burney_1D » Tue Feb 14, 2017 12:16 am

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
Posts: 22
Joined: Fri Jul 15, 2016 3:00 am

Re: Winter 2013 Midterm Q2A

Postby emilyharland » Tue Feb 14, 2017 4:26 pm

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


Return to “Heat Capacities, Calorimeters & Calorimetry Calculations”

Who is online

Users browsing this forum: No registered users and 1 guest