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Enthalpy change

Why can't you directly measure the enthalpy change for the conversion of the blue hydrated copper (II) sulfate crystals into the white anhydrous crystals?

Also, why can't you measure the enthalpy change directly of a combustion reaction of ethane from that spirit burner experiment (forgot the actual name)
Reply 1
Avatar for Pigster
Pigster
20
Look up the boiling temperature of ethane.
Original post by CookieHero
Why can't you directly measure the enthalpy change for the conversion of the blue hydrated copper (II) sulfate crystals into the white anhydrous crystals?

Also, why can't you measure the enthalpy change directly of a combustion reaction of ethane from that spirit burner experiment (forgot the actual name)


For the first one, it's difficult to precisely measure temperature changes of solids like copper sulphate crystals - its far easier to create a Hess's Law cycle and measure the enthalpy change of dissolving both individually in water
Reply 3
Avatar for CookieHero
CookieHero
OP
3
Original post by TheHobbit
For the first one, it's difficult to precisely measure temperature changes of solids like copper sulphate crystals - its far easier to create a Hess's Law cycle and measure the enthalpy change of dissolving both individually in water


Thanks
Reply 4
Avatar for metaljoe
metaljoe
7
Reactions where we want to find out the enthalpy change are always carried out under standard conditions. However, in real life it is very hard to maintain standard conditions in a combustion reaction, which means that working out the enthalpy change directly may not be entirely accurate. Hence we use hess's law to work it out indirectly and get a more accurate answer. Hope I made sense and helped you out.
Reply 5
Avatar for oni176
oni176
7
I believe it is because the activation energy is too high

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