1. Aqueous silver ion reacts with aqueous chloride ion to ...

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 = [4∆Hf0CO2 + 2∆Hf0 H2O]-[2∆Hf0C2H2+ 5∆Hf0 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.

∆V = 18.0 L – 12.0 L = 6.0L W = -P = 0.975 atm x 6.0 L = -585L.atm x 101.325 J/ L. atm = 593 J (we say evolved so positive) V = 6.0L X (1000ml/1L) X (1cm3/1ml) = 6000 cm3

h= 6000 cm3 / π x (8.50 cm)2 = 26.4 cm