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This website and my lecturer have describe negative enthalpies that are becoming less exothermic as decreasing. A relevant diagram from the linked to website to illustrate what I mean:

enter image description here

I see the enthalpy of hydration is decreasing in magnitude but it is becoming more positive so why is it said to decrease? Is this a convention of some sort?

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  • $\begingroup$ It is used this way because the values are closer to zero, i.e. the relative magnitude is smaller ignoring the sign because the signs are the same. But it can be confusing: what if the hydration was +322, then one would have to say it had increased. $\endgroup$ – porphyrin Jun 12 '18 at 12:40
  • $\begingroup$ @porphyrin If I'm not mistaken, hydration enthalpies are always exothermic, right? Likewise for lattice formation enthalpy. And thank you for your comment, this makes more sense now. $\endgroup$ – whois Jun 12 '18 at 15:23
  • $\begingroup$ I was just giving an example irrespective of being correct chemically :) $\endgroup$ – porphyrin Jun 12 '18 at 17:05

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