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    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:
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    (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
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    (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?
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    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.
 
 
 
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