# Hard enthalpy change a level exam question help!!!

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Thread starter 1 year ago
#1
This is the whole question:
This question is about copper (II) sulfate, CuSO4, and sodium thiosulfate, Na2S2O3.
a) Enthalpy change of reaction for converting anhydrous copper (II) sulfate to hydrated copper (II) sulfate is difficult to measure directly by experiment.
CUSO4(s) +5H2O (l) = CuSO4.5H2O(s) reaction 5.1
The enthalpy changes of solution of anhydrous and hydrated copper (II) sulfate can be measured by experiment. Reactions shown below.
In equations, 'aq' represents excess water.
CuSO4(s) + aq = Cu2+(aq) + SO4 2-(aq) reaction 5.2
CuSO4.5H2O (s) + aq = Cu2+(aq) + SO4 2-(aq) reaction 5.3
Experiment 1- find enthalpy change of solution of CuSO4 (s) for reaction 5.2
Method- weigh bottle with CuSO4(s) and weigh polystyrene cup. add 50cm3 water to cup and measure temp. add CuSO4(s), stir,measure final temp. weigh empty bottle, weigh cup with final solution.
Mass readings- Mass bottle + CuSO4 28.04
Mass empty bottle 20.06
Mass of polystyrene cup 23.43
Mass polystyrene cup + final solution 74.13
Temp readings- initial temp of water 20.5
temp of final solution 34.0

Experiment 2- same method as experiment 1 but with CuSO4.5H2O. student calcs enthalpy change of solution of CuSO4.5H2O as +8.43kjmol-1
i) calc enthalpy change of solution of CuSO4 (s) for reaction 5.2 and determine enthalpy change of reaction 5.1. assume specific heat capacity of solution is same as for water. show working and include energy cycle linking enthalpy changes
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2 months ago
#2
is the enthalpy change of the solution of CuSO4 -56.43 KJmol^-1
not sure how to calculate the enthalpy change for reaction 5.1 though
could be totally wrong lol
workings 50x4.18x13.5=2821.5j=2821.5kj
7.98/159.6=0.05 mols of copper sulfate
2.8215/0.05=-56.43kjmol^-1
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1 month ago
#3
(Original post by gracebx1)
is the enthalpy change of the solution of CuSO4 -56.43 KJmol^-1
not sure how to calculate the enthalpy change for reaction 5.1 though
could be totally wrong lol
workings 50x4.18x13.5=2821.5j=2821.5kj
7.98/159.6=0.05 mols of copper sulfate
2.8215/0.05=-56.43kjmol^-1
How'd you get 50 for m?
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