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# Write a full equation, including state symbols,for the formation of MgO... watch

1. ...from its elements

This is what I thought it was 2Mg(s) + O2(g)---> 2MgO(s)

but the books answer says Mg(s) + 1/2 O2(g)---> MgO(s)

why have they done that? I really don't understand, please explain

thank you
2. They are both right; some people like the second as you have less numbers everywhere, and I favour it too. All that matters are that the ratios are the same.

e.g. 4X + 2Y ---> 2X2Y
is the same as 2X + Y ---> X2Y
Is the same as X + 1/2Y ----> 1/2X2Y
They are both right; some people like the second as you have less numbers everywhere, and I favour it too. All that matters are that the ratios are the same.

e.g. 4X + 2Y ---> 2X2Y
is the same as 2X + Y ---> X2Y
Is the same as X + 1/2Y ----> 1/2X2Y
ok thank you, another quick question , do you think I would not get the mark if that was a question in an exam?
4. (Original post by BuuTuu)
...from its elements

This is what I thought it was 2Mg(s) + O2(g)---> 2MgO(s)

but the books answer says Mg(s) + 1/2 O2(g)---> MgO(s)

why have they done that? I really don't understand, please explain

thank you
Is this to do with the Enthalpy change topic and the 'enthalpy change of formation'?
If so, remember that it is the formation of ONE mole of a compound, which is made in the second equation.
5. (Original post by BuuTuu)
ok thank you, another quick question , do you think I would not get the mark if that was a question in an exam?
Yes, either lowest whole numbers or halves are fine, or at least they were/are for my exam board (Edexcel) Good luck

Unless as the above said, they were asking for the equation for enthalpy change of formation.
6. Formation will generally be forming one mol of substance.

OCR didn't allow formation of 2 or more mols for a Enthalpy change definition, so I'd say only the second one is correct.
7. Either is right, personally, I prefer your answer, it means you don't have half moles

EDIT: oh for gods sake can't someone have an opinion?
8. As long as the ratios are the same, you should be fine
So what the book says, what you said and the guy above me said are correct
9. ok, thanks everyone
10. (Original post by EffKayy)
Is this to do with the Enthalpy change topic and the 'enthalpy change of formation'?
If so, remember that it is the formation of ONE mole of a compound, which is made in the second equation.
This.

(Original post by BuuTuu)
...from its elements

This is what I thought it was 2Mg(s) + O2(g)---> 2MgO(s)

but the books answer says Mg(s) + 1/2 O2(g)---> MgO(s)

why have they done that? I really don't understand, please explain

thank you
11. (Original post by BuuTuu)
ok, thanks everyone
12. (Original post by EffKayy)
no, I have no idea what that is
13. I love how everyone's asking about enthalpy changes when OP's probably just started GCSEs :P
14. (Original post by The Tesco Jinn)
I love how everyone's asking about enthalpy changes when OP's probably just started GCSEs :P
lol, nope just started AS
15. Salters by any chance?
16. (Original post by BuuTuu)
lol, nope just started AS
Oh, oops, my bad sorry . But yeah same, Well...IB anyway
17. (Original post by The Tesco Jinn)
Oh, oops, my bad sorry . But yeah same, Well...IB anyway
lol

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Updated: October 29, 2011
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