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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: electrogeek on May 04, 2019, 10:53:01 AM

Title: Dispersion formula mystery...
Post by: electrogeek on May 04, 2019, 10:53:01 AM
Hi everyone,

I have been given the question that I've attached below about the use of the London formula to calculate the energy of interaction. I don't understand why the answer is positive however because I got a value of -8.74 kJ per mole...

Because all the numbers are positive which are going into the formula, the answer has to be negative like what I have calculated? Any help would be great because I've had another question on this formula and the same thing happens there where the answer is given to be positive but I calculate a negative value.

Cheers
Title: Re: Dispersion formula mystery...
Post by: Borek on May 05, 2019, 03:40:21 AM
Perhaps it is a matter of convention - are you asked about energy of interactions, or energy of formation?
Title: Re: Dispersion formula mystery...
Post by: mjc123 on May 07, 2019, 05:46:31 AM
Since the same symbol V is used in question and answer, it ought to refer to the same thing, and therefore be negative.
Title: Re: Dispersion formula mystery...
Post by: electrogeek on May 09, 2019, 01:59:03 PM
Thanks for the replies. I will have to ask my lecturer because on some revision problems which are about the same idea the values for V are negative in his mark scheme.

Thanks for checking though - just wanted to make sure there wasn't something that I was missing.