username3835832
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http://pmt.physicsandmathstutor.com/...%20Entropy.pdf

question 4ii
Seems like you have to add up both numbers to get the answer and I don't get it? also why is the answer a positive and not a negative number??

answer from markscheme:
negative sign (only if a calculation) (1)
883 kJ mol–l (1)
(only give both marks if working and answer correct)
hydration / solvation enthalpies (of Li+ and Cl–
) (1)
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charco
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(Original post by chemquestion)
http://pmt.physicsandmathstutor.com/...%20Entropy.pdf

question 4ii
Seems like you have to add up both numbers to get the answer and I don't get it? also why is the answer a positive and not a negative number??

answer from markscheme:
negative sign (only if a calculation) (1)
883 kJ mol–l (1)
(only give both marks if working and answer correct)
hydration / solvation enthalpies (of Li+ and Cl–
) (1)

You have to construct a cycle showing the relationship between lattice enthalpy, hydration enthalpy and the enthalpy of solution.

MX(s) --> M+(g) + X-(g) is the endothermic lattice enthalpy
MX(s) --> M+(aq) + X-(aq) is the dissolution enthalpy
M+(g) + X-(g) --> M+(aq) + X-(aq) is the hydration enthalpy

From the above you should see that subtracting:

dissolution energy - lattice enthalpy = hydration enthalpy

rearrange as required.
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