A-level chemistry OCR A definitions

I've found that the definitions my chemistry teacher teach us, the definitions in OCR-approved textbooks, and the definitions on the OCR spec are all different. I'm trying to find out the simplest definitions that would still score full marks on an exam. Currently, I'm between playing it safe and remembering the longer definitions with all 3 sources taken into account or going for the simpler spec definitions, but these seem too simple and good to be true.

for example, here are some differences:

definition of enthalpy change of hydration:
Textbook- enthalpy change that occurs when 1 mole of a gaseous ion is completely hydrated by water
Spec- enthalpy change when dissolving 1 mole of gaseous ions in water

Definition of 1st ionisation energy:
textbook- the energy required to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
Spec- energy required to remove 1 mole of electrons from 1 mole of gaseous atoms

It would be a great help if anyone could guide me on which definitions I should use, thanks

I've been recommended to use the definitions in the following textbook, as it is written by OCR's chief examiner.
A Level Chemistry for OCR A Student Book (Ocr a Level) Paperback – 23 Jul 2015
by Rob Ritchie (Author), Dave Gent (Author)

I've had a look at that book and it seems to be getting a lot of positive feedback, the textbook definitions I found were from the other OCR approved textbook which doesn't seem as spec-based so I might have a try at this one you've recommended if I do buy a textbook, thanks. Problem is I've been recommended by my teacher to stick to what he teaches, but I'm not sure if that's just bias, so I'm still running in circles of what to trust

alternatively, if you look on OCR's website at the spec, mixed within it does have the definitions, although that would take a lot more time.

I've already done that and that's the thing, I've heard from some mates that the definitions on the spec aren't the same as what you would be awarded for in an exam, I kind of believe that because it seems too simple to be true.

What the specification says will always be awarded full marks. If ANY textbook says something different to the specification then the spec rules. Some textbooks were written before the spec. was finished, so may contradict the spec. but the spec wins. Every. time.

If you read mark schemes for recent exams, this will support my claim. The guidance (on the right of the MS) may ALLOW wording that is more like textbooks, but I recommend (for reasons I can't be bothered to elaborate on) not using the wording in the guidance and to suggest sticking to the wording on the LHS.

BTW, there is no longer such a thing as "chief examiner".

Thank you very much for clearing things up, this will help my revision a lot. I now have a list of all or at least 98% of all the definitions on the spec. Took a while scanning the whole spec but it's worth the A* and thanks to the previous person for helping

One thing to add: it is well worth learning definitions, but don't expect to be asked for them in your exams.

The old (F321-325) papers loved to ask for them, but on the current spec. there will be virtually no questions asking for them; it will all be application of the definitions.