# Enthalpy A Level Chemistry Question

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#1
If someone could help me with this question, I'd really appreciate it.

Under some circumstances, methane reacts explosively with chlorine to give carbon and hydrogen chloride:
CH4 + 2Cl2 --> C + 4HCl
Estimate the enthalpy change for this reaction.
Mean bond enthalpies:
C-H= +413
Cl-Cl = 243
H-Cl= +432
Enthalpy change of atomisation of carbon: +717

I'm in Year 12 and on my spec (OCR A), atomisation doesn't come up until Year 13. My teacher has given me this sheet though, so I'm guessing that I should be able to apply my knowledge somehow?
1
1 year ago
#2
I'm in year 12 too, and our spec doesn't cover atomisation either. However, i'm guessing:

Reactant bond enthalpy = 4 C-H + 2 Cl-Cl = 4x413 + 2x243 = 2138
Product bond enthalpy = 4 H-Cl = 4x432 = 1728

ΔH = 2138 - 1728 - the enthalpy change of the atomisation of carbon = -307 kJ/mol
Last edited by ng849; 1 year ago
2
1 year ago
#3
You don't need to worry about the atomisation - that's usually for Born-Haber Cycles and is not relevant to the question. It may have been a multi-part question and the teacher simply hasn't removed this part.

You should be able to work out with the information you have otherwise
1
#4
(Original post by ng849)
I'm in year 12 too, and our spec doesn't cover atomisation either. However, i'm guessing:

Reactant bond enthalpy = 4 C-H + 2 Cl-Cl = 4x413 + 2x243 = 2138
Product bond enthalpy = 4 H-Cl = 4x432 = 1728

ΔH = 2138 - 1728 + the enthalpy change of the atomisation of carbon = 1127 kJ/mol
Good try (I attempted the question the same way you did) but the answer is -307 kJ/mol.
0
1 year ago
#5
hmmm
Last edited by username5120904; 1 year ago
0
1 year ago
#6
(Original post by studyingpeach)
If someone could help me with this question, I'd really appreciate it.

Under some circumstances, methane reacts explosively with chlorine to give carbon and hydrogen chloride:
CH4 + 2Cl2 --> C + 4HCl
Estimate the enthalpy change for this reaction.
Mean bond enthalpies:
C-H= +413
Cl-Cl = 243
H-Cl= +432
Enthalpy change of atomisation of carbon: +717

I'm in Year 12 and on my spec (OCR A), atomisation doesn't come up until Year 13. My teacher has given me this sheet though, so I'm guessing that I should be able to apply my knowledge somehow?
2
#7
(Original post by Meowmeownerd1)
Thank you so much - that's really useful!
0
1 year ago
#8
(Original post by studyingpeach)
Thank you so much - that's really useful!
Anytime 😊
0
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