The Student Room Group

Enthalpy reaction

In an experiment to measure the enthalpy change of a reaction involving gases,which of the following conditions must always be kept constant?
A) Pressure
B )Temperature
C )Volume
D )Temperature and pressure
Reply 1
What do you think it is?

(and why that and not the others?)
Original post by Pigster
What do you think it is?

(and why that and not the others?)

I think the answer is d but the answr is a
Reply 3
Original post by Ailurophile03
I think the answer is d but the answr is a

I thought it was D too, but maybe it's A because when the reaction occurs temperature will change depending on whether the reaction is exothermic or endothermic, so if you kept temperature constant, you wouldn't actually be able to measure the temperature change, which is what you do when you work out the enthalpy change. The enthalpy change for a reaction is the heat energy change measured under conditions of constant pressure.
c is the answer
By definition, an enthalpy change is the change in heat energy under a constant pressure.

It has to be A and not B or D as if the temperature was constant, it’d be impossible to measure the change in heat energy.

As for C, I’m pretty sure that’s for internal energy.
(edited 1 year ago)

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