## test question 7 [ENDORSED]

$\Delta U=q+w$

Melissa Per 2J
Posts: 32
Joined: Fri Sep 29, 2017 7:04 am

### test question 7

The question from the test is: In order to make iced tea a 50.0 g ice cube at 0.0 degrees Celcius is added to 250 mL of tea at 20.0 degrees Celcius. What is the final temp. of the iced tea once it has reached themal equilibrium? Assume no heat is transferred to or from the surroundings. Density of [iced tea] is 1.00g/mL over the range 0-25 degrees Celcius.

Please help. How do I find the initial delta H?

Thu Uyen Tran 1B
Posts: 31
Joined: Fri Sep 29, 2017 7:05 am

### Re: test question 7

What do you mean initial deltah? All of them were given on the equations sheet. Unless you were talking about the calculation of the phase change?

Kyung_Jin_Kim_1H
Posts: 53
Joined: Thu Jul 27, 2017 3:00 am

### Re: test question 7

I don't think we need to know initial deltaH...?

What I did was reason that the heat exudes by the ice cube will be the same amount of heat absorbed (so same number just different signs) by the iced tea.

That means that the q from phase change of ice (solid--> liquid) + mC(Tfinal - Tinitial) = -mC(Tfinal- Tinitial).

Clarisse Wikstrom 1H
Posts: 63
Joined: Fri Sep 29, 2017 7:05 am

### Re: test question 7

I think the "inital deltaH" that you are thinking of is the deltaH(fus) of water, which is needed for the phase change of the ice cube to liquid water. The other steps only require q=mCdeltaT

Lily Guo 1D
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Joined: Fri Sep 29, 2017 7:03 am

### Re: test question 7

delta H (fusion) of ice would have been given

Anne 2L
Posts: 35
Joined: Fri Sep 29, 2017 7:05 am

### Re: test question 7

Yes, Delta H (fusion) for water was given. We were supposed to treat the tea as if it was just water.

Nehal Banik
Posts: 64
Joined: Thu Jul 13, 2017 3:00 am

### Re: test question 7  [ENDORSED]

First you have to set both equations equal to one another, so you are trying to find the final temperature right? So you multiply the enthalpy of fusion of ice times the moles of ice plus the energy needed to cause the melted ice, now water to reach the final temperature. You take that equation and set it equal to the energy required to change the temperature of the water, because since the ice is added to the water, it will cause a decrease in temperature for the water as it cools.

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