Re: heat of solution

In article <8W%Je.3021$Wi6.2624@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>, John Doe III <john_doeIII@xxxxxxxxx> wrote:
: ExamCrackers pg 82, problem 97

: 20 grams of NaCl is poured into a coffee cup calorimeter containing 250 ml
: of water. If the temperature inside the calorimeter drops 1 C by the time
: NaCl is totally dissolved, what is the heat of solution for NaCl and water?
: (specific heat of water is 4.18 J/gC)
: A. -3 KJ/mol
: B. -1 KJ/mol
: C. +1 KJ/mol
: D. +3 KJ/mol
: I'll post their solution but I don't want to do it now because I don't like
: biased explanations. Thank you so much in advance.

(0) What is the definition of heat of solution?
(1) What are the correct units of the final answer?
(2) How many moles of NaCl were added to the solution?
(3) How much energy does it take to raise or lower 1/4 L of water 1 degree?
(4) Is the reaction exothermic or endothermic?
(5) How can you arrange the answers to (2), (3), and (4) to give a number
with the correct units (according to (1)) and the correct sign (according
to (0))?

-----
Richard Schultz schultr@xxxxxxxxxxxxxx
Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel
Opinions expressed are mine alone, and not those of Bar-Ilan University
-----
"an optimist is a guy/ that has never had/ much experience"
.

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