Big-Daddy
Badges: 13
Rep:
?
#1
Report Thread starter 8 years ago
#1
How is the enthalpy change of atomisation defined a) for an element and b) for a compound? I have two conflicting definitions:

a) The enthalpy change of atomisation for an element is the enthalpy change when 1 mole of gaseous atoms are formed from the element in its standard state, under standard conditions. e.g. 1/2 Cl2 (g) -> Cl (g)

b) The enthalpy change of atomisation for a compound is the enthalpy change when 1 mole of the compound in its standard state is reduced to its constituent gaseous atoms, under standard conditions. e.g. C3H6 (g) -> 3 C (g) + 6 H (g).

These seem to conflict with each other to me. :confused:
1
reply
AishaTara
Badges: 14
Rep:
?
#2
Report 8 years ago
#2
(Original post by Big-Daddy)
How is the enthalpy change of atomisation defined a) for an element and b) for a compound? I have two conflicting definitions:

a) The enthalpy change of atomisation for an element is the enthalpy change when 1 mole of gaseous atoms are formed from the element in its standard state, under standard conditions. e.g. 1/2 Cl2 (g) -> Cl (g)

b) The enthalpy change of atomisation for a compound is the enthalpy change when 1 mole of the compound in its standard state is reduced to its constituent gaseous atoms, under standard conditions. e.g. C3H6 (g) -> 3 C (g) + 6 H (g).

These seem to conflict with each other to me. :confused:
nope they have the same meaning but one is talking in terms of an element and the other of a compound
I'd go with the first oen as its easier to remember as its easier to remember
0
reply
Big-Daddy
Badges: 13
Rep:
?
#3
Report Thread starter 8 years ago
#3
(Original post by AishaTara)
nope they have the same meaning but one is talking in terms of an element and the other of a compound
I'd go with the first oen as its easier to remember as its easier to remember
The meanings are obviously different. You don't think there's a difference between an arbitrary number of moles going to 1 mole of gaseous atoms, and 1 mole of a compound going to an arbitrary number of gaseous atoms?

The question comes down to whether I just have to accept that there is this difference in definition, or is one of the two definitions I've given wrong?
0
reply
19alex91
Badges: 0
Rep:
?
#4
Report 8 years ago
#4
Well they don't conflict because one is in relation to an element, and one is in relation to a compound.

If you had elemental carbon in some form whether it was graphite or diamond etcetera, and you heated that carbon to form a vapour and all of it was completely vaporized then you would have the same number of moles of carbon as you did in the solid before it was vaporized now in the gaseous state. Those atoms haven't changed in mass so the weight of one mole remains the same. So heating one mole of the element would produce one mole of the vapour which would give the same definition as that for the compound.

For the compound however heating it to the point where all the atoms seperates means that you no longer have the starting material. If you heated table salt to the point that it vaporised, you would no longer have the ionic lattice consisting of sodium and chloride ions as you did in the solid, but you would infact have a gaseous cloud of sodium and chloride ions. 1 Mole of NaCl would therefore give you 1 mole of sodium ions and 1 mole of chloride ions.

Both the definitions use the different wording, but I think this is just due to the property of the elements that they would give the same number of moles upon heating. Whereas the compound would give differnt number of moles for all the constituents to the previous single value you had.
0
reply
SmallStudent123
Badges: 1
Rep:
?
#5
Report 1 year ago
#5
But surely if you have a diatomic molecule like chlorine and you break it up into atoms you will then have twice as many moles as you did to begin with.This would mean that the definitions do contradict, as if you were to start with 1 mole for an element in its standard state, you wouldn't necessarily end up with 1 mole of atoms.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

How would you feel if uni students needed to be double vaccinated to start in Autumn?

I'd feel reassured about my own health (32)
15.76%
I'd feel reassured my learning may be less disrupted by isolations/lockdowns (63)
31.03%
I'd feel less anxious about being around large groups (24)
11.82%
I don't mind if others are vaccinated or not (17)
8.37%
I'm concerned it may disadvantage some students (11)
5.42%
I think it's an unfair expectation (53)
26.11%
Something else (tell us in the thread) (3)
1.48%

Watched Threads

View All