Homework Help: chemistry

Posted by sam on Wednesday, September 26, 2012 at 1:06pm.

KCl(s) → K+(aq) + Cl‾ (aq)

Solid KCl dissolves as shown in the above equation. A 6.60 g sample of KCl was dissolved in 42.3 g of water. The initial temperature of the water was 21.90°C. After the compound dissolved, the temperature of the water was 10.20°C. Assume the heat was completely absorbed from the water and no heat was absorbed by the reaction container or the surroundings. Calculate the heat of solution of KCl in kJ/mol. The specific heat of water is 4.184 J/g·°C. (Do not take the added mass of the KCl into account when calculating q for the solution.)

chemistry - DrBob222, Wednesday, September 26, 2012 at 2:54pm
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)

That gives you q/6.60g KCl = q/gram.
To convert to q/mol it will be
q/6.60 x (molar mass KCl/1 mol) = ? J/mol
Convert to kJ/mol.
chemistry - sam, Wednesday, September 26, 2012 at 5:33pm
q= 4.184(42.3)(10.2-21.9)
= -2070.70 J
-2070.70J/6.60g KCl = -313.74 J/g
-313.74 J/g(74.55g/ 1 mol KCl)= -23389.32J/mol
-23.4 kJ/mol
Is this correct?

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