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darmabiala
Nov 24, 2009, 10:33 PM
The calorimeter is prepared with 44.96 g of water, both at 22.6 Celsius. 2.42 g of salt are

dissolved in the water ( note the total solution mass) and the temperature falls to 19.9

Celsius . Calculate the heat of the solution for the salt. If the salt is potassium chloride,

calculate the molar heat of solution.

1. Finding the heat of solution for the salt:

water:
m = 44.96 g
T initial= 22.6 Celsius
T final= 19.9 Celsius

Salt:
m= 2.42 g
T initial= 22.6
T final= 19.9 Celsius

delta T = 2.7 Celsius
C = 4.184 J/ g Celsius

delta Q = mC delta T
= (44.96 g) ( 4.184 J/g celcius) ( 2.7 celcius)
= 507. 90 J

2. Finding the molar heat of the solution: ( really not sure about this)

m = 44.96 g
MW = 74.55 g/mol

mol = m/MW
= 44.96 g / 74.55 g/mol
= 0.603 mol

Molar heat: heat/mol
507. 90 J /0.603 mol
= 842.3 J/mol
=842.3 x 10 -3 KJ/mol

Unknown008
Nov 25, 2009, 10:25 AM
For the second part:

You're right to be not sure.

You have found that 2.42 g of KCl absorb 507.9 J.
How many moles if 2.42 g of KCl? Because you have to find the energy absorbed by 1 mole of KCl.

So, using the MW, 2.42 g is 0.0325 mol
Therefore, 0.0325 mol of KCl absorb 507.9 J.

How much heat is absorbed by 1 mol of KCl?

I hope it helped! :)

darmabiala
Nov 25, 2009, 10:50 PM
Yes, it did help thank you so much