Australia working with energy and gas (5)
I believe the answer is:
ozone
'gas' is the definition.
(I know that ozone is a type of gas)
'australia working with energy' is the wordplay.
'australia' becomes 'oz' (informal name for Australia).
'working' becomes 'on' (on can mean working or activated).
'with' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'oz'+'on'+'e'='OZONE'
'and' acts as a link.
(Other definitions for ozone that I've seen before include "Atmospheric gas shielding us from ultraviolet radiation" , "Form of atmospheric oxygen" , "something refreshing" , "Layer that protects against ultraviolet rays" , "Less common form of oxygen" .)