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Entropy A2 Chem please help

I calculated the electron affinity which is -347.5kJ mol^-1, which is correct. In part b, first I found the entropy value by doing (63+223)-124=162JK^-1mol^-1

I tried to use deltaH = TdeltaS (Since deltaG=<0 as this is when the reaction becomes geasible thus can be ignored)

Mark scheme says deltaH = 859 * 10*10*10 = 162*T but I've no idea why they're doing this.

I'm not sure what to do next... Please help. Thank youu xx
Reply 1
Curious way of writing it.

The thing you're missing (and soooo many students do this) is the mismatch between the units for DH and DS. DH is in kJ mol-1, whereas DS is J K-1 mol-1.

You have to convert them to the same version of J. One way to do this, is to multiply the DH by 1000 (which is the same as 10*10*10).
Original post by Pigster
Curious way of writing it.

The thing you're missing (and soooo many students do this) is the mismatch between the units for DH and DS. DH is in kJ mol-1, whereas DS is J K-1 mol-1.

You have to convert them to the same version of J. One way to do this, is to multiply the DH by 1000 (which is the same as 10*10*10).


Oh yes yes yes, of course. But what about the 859? Why is the enthalpy of formation being used rather than the enthalpy of atomisation etc? Thanks in advance!
Reply 3
DfH (BaCl2) is the reverse reaction of the equation given in part (b), so will have the same magnitude only opposite sign.

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