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Lecture

CHEM 1000 Lecture Notes - Silver Chloride, Joule, Heat Capacity


Department
Chemistry
Course Code
CHEM 1000
Professor
Hameed A.Mirza

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1. Aqueous silver ion reacts with aqueous chloride ion to yield a white
precipitate of silver chloride.
Ag+ + cl- agcl
When 10.0 ml of 1.00 M AgNo3 is added to 10.0 ml of 1.00 M Nacl solution at 25C
in a calorimeter a white precipitate of Agcl forms and the temperature of the
aqueous mixture increases to 32.6C Assuming the specific heat of the aqueous
mixture is 4.18 J/gC the density of the mixture is 1.00 g/ml, calorimeter absorbs
negligible heat. Calculate H in kJ in the reaction.
Ans.
* Balance the equation first! In such cases
m = 20.0 ml x 1 g/ml = 20 g
T = 32.6C 25.0C = 7.6C
q = 4.18 J/gC x 20.0 g x 7.6C = 6.4 x 102 J
moles of Ag+ = 10.0 ml X (1.00 mol Ag+ / 1000 ml ) = 1.00 X 102 mol Ag+
Therefore, moles of AgCl
Heat evolved / mole AgCl = 6.4 X102 J / (1.00 X 10-2 mol AgCl) = -64 KJ/ mol Agcl
*Either mention heat is evolved or put the negative sign
2. Oxyac welding torches burn acetylene gas C2H2O. calculate H in KJ for
combustion reaction of acetylene to yield Co2 and H2O
Hf , C2H2 = 227.4 KJ/mol
H2O = -241.8 KJ/mol
CO2 = -393.5 KJ/mol
Ans.
*First step balance the equation
2C2H2 (g) + 5O2 (g) 4CO2 (g) +2H2O(g)
Hf = [4Hf
0CO2 + 2Hf
0 H2O]-[2Hf
0C2H2+ 5Hf
0 O2]
= [4mol x -393.5 KJ /mol + 2mol x -241.8 KJ/mol]-[2mol + 227.4 KJ/mol]
=
3. A reaction inside a cylindrical container with a moveable piston causes
volume change from 12.0L to 18.0L while the pressure on outside the
container remain constant at 0.975 atm. What is the value in J of the work
w done during the reaction?  
Ans.
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