BR Themodynamics question

[capostat]

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What is the highest Temperature reached after 40 grams of CaCl2 are added to 200ml of water at 20C?

Information in passage: "Ten grams of calcium chloride can raise the temperature of 100ml of water approximately 18 degrees."

This question really frustrated me, because in the entire chapter, there was not one example of a solute dissolved in a solvent--all the sample problems used water added to water. And then on top of that, the answer given was basically,--"since the passage said this, this means the answer is that".

Please help with the actual solution to the problem. The answer is 56C*.

(*edited).

 

[kentavr]

1. Heat produced by 10g: Q1 = c*m*deltaT = c * 100 * 18 = 1800*c
where c - specific heat capacity of solution
2. 40g produce 4times more heat Q2 = 4*Q1 = 4*1800*c
3. Change in T for 200 ml :
DeltaT = Q2/(c*m2) = 4*1800*c/(200*c) = 4*9=36C

The answer is estimation, since it does not include the heat needed to heat the CaCl2 itself.
HTH

 

[Dr Gerrard]

I would think it would be 36 + 20, or 56.

The question asked for highest temperature, not temperature change.

 

[matth87]

I would think it would be 36 + 20, or 56.

The question asked for highest temperature, not temperature change.

lol I think the BR book just got owned...

sometimes I really wonder about these prep books...

 

[capostat]

1. Heat produced by 10g: Q1 = c*m*deltaT = c * 100 * 18 = 1800*c
where c - specific heat capacity of solution
2. 40g produce 4times more heat Q2 = 4*Q1 = 4*1800*c
3. Change in T for 200 ml :
DeltaT = Q2/(c*m2) = 4*1800*c/(200*c) = 4*9=36C

The answer is estimation, since it does not include the heat needed to heat the CaCl2 itself.
HTH

Thanks.


Yes the answer is 56 actually. I was so worked up about how the heck did they get 36 for delta T, that it slipped into my post.