Question

12 If white anhydrous copper(II) sulfate powder is left in the atmosphere it slowly absorbs water vapour giving the blue pentahydrated solid. Cuso (s) + SH,O(1) CuSO, SH,O(s) (anhydrous) (pentahydrated) It is difficult to measure the enthalpy change for this reaction directly. However, it is possible to measure the heat changes directly when both anhydrous and pentahydrated copper(II) sulfate are separately dissolved in water, and then use an energy cycle to determine the required enthalpy change value, AH,, indirectly. AH Cuso (s) + SH.(I) CuSO,SH.0(s) AH AH, Cuso,(aq) (a) To determine AH, a student placed 50.0 g of water in a cup made of expanded polystyrene and used a data logger to measure the temperature. After two minutes she dissolved 3.99 g of anhydrous copper(II) sulfate in the water and continued to record the temperature while continuously stirring. She obtained the following results. 27 Max predicted TWW no heat loss 26 AD Temperature /°C 0 100 200 300 400 500 600 700 800 900 1000 1100 Time's

Answer 1

The initial temperature is 19.1 deg C

The final temperature is 26.1 deg C

The temperature change

AT = T, -T; AT = 26.1°C – 19.1°C AT = 7°C

Assume the specific heat of solution to be equal to that of water

C= 4.1801 – 9°C

The mass of solution

3.99 g + 50.0 g = 53.99 g

Irun = WXC XAT Grun = 53.99 g x 4.1801 - 9. 0C x 70 Crun = 1579.8 J

Convert unit from J to kJ

[ 1 ᎬᎫ qrun = 1570.8 Ꭻ x 1000 Ꭻ qrun = 1.57Ꮽ8 kᎫ .

Arxn = -4run qren = -1.5798 kJ

The mass of anhydrous copper(II) sulfate is 3.99 g.

The molar mass of anhydrous copper(II) sulfate is 159.6 g/mol

The number of moles of anhydrous copper(II) sulfate is

3.99 g 159.6 g/mol = 0.025 mol

-1.5798 kJ AH = 0.025 mol AH = -63.2 kJ/mol