# Enthalpy of formation equationWatch

#1
for just say SO2.

Would it be:

S(s) + O2(g) --> SO2(g)

or

S8(g) + 802(g) --> 8SO2(g) i know this is a multiple, and isnt a formation eq as its 8 moles but sulphur exist as s8. so???? explain some one.

also

if we wanted phosphorus tribromide

it would be p4 + 6br2 --> 4pbr3, as it exists as p4. but wud enthalpy eq be p + 3/2br2 --> pbr3.

But how could this work when enthalpy of formation is one mole of substance under standard conditions but these elements exist as tetra or di, wud we do this...

1/8S8 + 02 --> so2

and 1/4p4 + 3/2br3 --> pbr3.

would we do this??? or would we just ignore that sulphur exist as s8 and phosphorus exist as p4 and just use p and s?
0
2 years ago
#2
for just say SO2.

Would it be:

S(s) + O2(g) --> SO2(g)

or

S8(g) + 802(g) --> 8SO2(g) i know this is a multiple, and isnt a formation eq as its 8 moles but sulphur exist as s8. so???? explain some one.

also

if we wanted phosphorus tribromide

it would be p4 + 6br2 --> 4pbr3, as it exists as p4. but wud enthalpy eq be p + 3/2br2 --> pbr3.

But how could this work when enthalpy of formation is one mole of substance under standard conditions but these elements exist as tetra or di, wud we do this...

1/8S8 + 02 --> so2

and 1/4p4 + 3/2br3 --> pbr3.

would we do this??? or would we just ignore that sulphur exist as s8 and phosphorus exist as p4 and just use p and s?
Hey,
1) suphur and phosphurus exist as pure elements in their standard states

2) the enthalpy change of formation is the mentally change accompanying the formation of ONE MOLE. Therefore it can't be S8 or P4 that react, because during formation it has to be 1 mole that forms, can't be 4 or 8

Make sure to learn this definition: the mentally change of formation is the enthalpy change accompanying the formation of one mole of a substance from its constituent, under standard conditions, with the reactant and products being in their standard states.

Hope that cleared things up
0
#3
(Original post by Maths help)
Hey,
1) suphur and phosphurus exist as pure elements in their standard states

2) the enthalpy change of formation is the mentally change accompanying the formation of ONE MOLE. Therefore it can't be S8 or P4 that react, because during formation it has to be 1 mole that forms, can't be 4 or 8

Make sure to learn this definition: the mentally change of formation is the enthalpy change accompanying the formation of one mole of a substance from its constituent, under standard conditions, with the reactant and products being in their standard states.

Hope that cleared things up
Sulfur is octatomic in its standard state tho, s8, so enthalpy change wudnt it not be 1/8s8 + 02 --> so2, which will still give one mole. All I'm saying is that sulfur is not S but it's s8 in its standard state. Or am I wrong
0
2 years ago
#4
Sulfur is octatomic in its standard state tho, s8, so enthalpy change wudnt it not be 1/8s8 + 02 --> so2, which will still give one mole. All I'm saying is that sulfur is not S but it's s8 in its standard state. Or am I wrong
I guess it can also be a solid the single element too.
only one mole can form hence it must be S (s)

just in case i was wrong, i googled it and found this so i assume i'm right, although you may want to double check with your tachers
0
#5
(Original post by Maths help)
I guess it can also be a solid the single element too.
only one mole can form hence it must be S (s)

just in case i was wrong, i googled it and found this so i assume i'm right, although you may want to double check with your tachers

lollo XD

no to form one mole we can have an eight of the s8, still get one mole.
0
2 years ago
#6

lollo XD

no to form one mole we can have an eight of the s8, still get one mole.
Oh haha, thanks , guess we all learn something new everyday

thank you, this will be useful for my A2 exams (as it still comes in!) and my AS f322 retakes haha

i assume you do AS now? do you do OCR A by any chance?
0
#7
(Original post by Maths help)
Oh haha, thanks , guess we all learn something new everyday

thank you, this will be useful for my A2 exams (as it still comes in!) and my AS f322 retakes haha

i assume you do AS now? do you do OCR A by any chance?
AS chemistry new spec 2016. :s good luck tho
0
2 years ago
#8
AS chemistry new spec 2016. :s good luck tho
Sorry, I thought with A-Level reform, there's no longer AS?
0
#9
(Original post by Maths help)
Sorry, I thought with A-Level reform, there's no longer AS?
there is AS exams, but they don't count if you do full course.
0
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