AS Chemistry Help: Enthalpy Change in Chain Alkanes

[psychedelia]

Hi, this question is really bugging me.
Thanks in advance.

Homework Statement

The difference between the enthalpy change of combustion if sucessive chain alkanes is around -650 kJ/mol

Homework Equations

Why does the value of enthalpy change of the sections of the chains have a different value...

That wasn't very clear was it?

The Attempt at a Solution

http://img516.imageshack.us/img516/5919/whyqf0.jpg

 

[GCT]

Hi, this question is really bugging me.
Thanks in advance.

Homework Statement

The difference between the enthalpy change of combustion if sucessive chain alkanes is around -650 kJ/mol

Homework Equations

Why does the value of enthalpy change of the sections of the chains have a different value...

That wasn't very clear was it?

The Attempt at a Solution

http://img516.imageshack.us/img516/5919/whyqf0.jpg

For one calculating the the enthalpy of a reaction using tabulated bond enthalpies is an estimation - the context around which the bond is situated may alter its common bond enthalpy. E.G. You may have utilized the bond enthalpy of the carbon hydrogen bond in methane however note that your current molecule is relatively unstable ... its been a while since I've faced this topic so the actual answer may be related to a distinctly unrelated matter.

 

[Blueshift5]

Dear student,

Thank you for reaching out for help with your chemistry question. Enthalpy change in chain alkanes can be a confusing topic, so I am happy to provide some guidance.

Firstly, it is important to understand that the enthalpy change of combustion is the amount of energy released or absorbed when a substance undergoes complete combustion. This value is typically negative, as energy is released in the form of heat during combustion reactions.

Now, to address your question about the difference in enthalpy change between successive chain alkanes. This difference can be attributed to the number of carbon-carbon bonds in each alkane. As the chain length increases, so does the number of carbon-carbon bonds. This means that more energy is required to break these bonds during combustion, resulting in a larger negative enthalpy change.

Additionally, the enthalpy change can also be affected by the type of bonds present in the molecule. For example, branched chain alkanes have a lower enthalpy change compared to their straight-chain counterparts due to the steric hindrance caused by the branching, which makes it easier for the bonds to break.

I hope this explanation helps to clarify the concept of enthalpy change in chain alkanes. If you have any further questions, please don't hesitate to ask. Keep up the good work in your chemistry studies!