Certain amount of energy? Then play around (8)

I believe the answer is:

enthalpy

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'certain amount of energy?' is the definition.
I can't tell whether this defines the answer.

'then play around' is the wordplay.
'around' indicates anagramming the letters.
'then'+'play'='thenplay'
'thenplay' with letters rearranged gives 'ENTHALPY'.

Can you help me to learn more?

(Other definitions for enthalpy that I've seen before include "Thermodynamic quantity" , "Function for physical chemists" , "Measure of energy" , "Total heat content of a system" , "Thermodynamic measure of total heat content" .)

I've seen this clue in The Guardian.

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