Finding the final temperature of a final solution. putting ice in soda/water

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Discussion Overview

The discussion revolves around a homework problem involving the calculation of the final temperature of a solution after adding ice to soda (treated as water). Participants explore the thermal interactions between the ice and the soda, considering heat transfer, specific heat capacities, and phase changes.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant calculates the heat gained by the ice and sets it equal to the heat lost by the soda, but arrives at a final temperature of 39 C, which they suspect is incorrect.
  • Another participant suggests that the issue may lie in the signs used in the calculations, implying a potential error in the heat transfer direction.
  • A different participant recommends converting all units to calories and grams, providing specific values for the specific heat of water and ice, as well as the latent heat of fusion for ice.
  • One participant argues against the necessity of converting to calories, stating that while it may simplify calculations for water, it complicates matters when phase changes are involved.
  • The original poster later indicates they have resolved the issue independently.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of using calories versus joules for the calculations, and there is no consensus on the correctness of the original calculations. The discussion remains unresolved regarding the final temperature calculation.

Contextual Notes

Participants highlight potential issues with unit conversions and the treatment of heat transfer signs, but do not resolve these concerns. The calculations involve assumptions about no heat transfer with the surroundings and the specific heat capacities of the materials involved.

Who May Find This Useful

Students working on thermodynamics problems, particularly those involving heat transfer and phase changes in mixtures of substances.

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Homework Statement


Suppose you have a 24 ounce mug of soda (treat as water) at room temperature, which is 22 C. Warm soda tastes bad, so you add 125 g of ice at -25 C to the soda. What is the temperature (in C) of the soda once all the ice melts and the solution reaches a uniform temperature? The heat of fusion is 6.01 kJ/mol and the heat of vaporization is 40.7 kJ/mol. The specific heat capacity of ice and water are 2.09 and 4.18 J/g-K, respectively. Assume no heat is transferred to the soda from the surroundings.


Homework Equations


q= (mass)(Specific heat)(change in temp); q=(moles)(delta-enthalpy)


The Attempt at a Solution


So I did q(soda lost)= q(ice gained). I found the q of the ice by (125g)(0--25)(2.09) + (125g)(1mol/18g)(6.01 KJ/mol)(1000J/KJ)= 48087.35 J. So now I set it equal to the q(soda). I had 24 oz of soda which is 681 grams: 48087.35= (681g)(4.18)(TempFinal-22). But then I get 39 C which is wrong I'd assume! Please help me by showing all the steps. Thanks!
 
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In general you are on the right track. Pay attention to signs, my bet is that that's where you got lost.
 
You should convert all units to calories and grams here;
specific heat of water = 1 cal/gram deg C
specific heat ice = .5 cal/gram deg C
latent heat of fusion ice = 80 cal/gram
Now take the 681 grams of soda from 22 deg C to 0 deg C and obtain 14982
calories
The 125 grams of ice will absorb 1562 calories going from -25 C to
0 C and will absorb 10000 cal melting
So now you have 806 grams of water at 0 deg C and 3420 calories.
Therefore 3420 calories = (Temp) ( 806 grams)
 
Last edited:
morrobay said:
You should convert all units to calories and grams here

There is no need for that. cal is a nice unit when working with water, but it loses its simplicity when you have a system in which water changes state of matter.
 
Yeah, thanks guys. I ended up figuring it out :)
 

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