Sophie.cerys
Badges: 13
Rep:
?
#1
Report Thread starter 1 year ago
#1
Why do larger alkanes release more energy than shorter alkanes? As energy is required to break a bond, so as there are more bonds to break in a longer alkane, why does it release more energy?
0
reply
Pigster
Badges: 19
Rep:
?
#2
Report 1 year ago
#2
(Original post by Sophie.cerys)
Why do larger alkanes release more energy than shorter alkanes? As energy is required to break a bond, so as there are more bonds to break in a longer alkane, why does it release more energy?
Aha, but after you've broken the [more] bonds, you can then form more bonds.

More energy is released breaking bonds than forming them (hence overall it is exothermic).
1
reply
charco
Badges: 17
Rep:
?
#3
Report 1 year ago
#3
(Original post by Pigster)
Aha, but after you've broken the [more] bonds, you can then form more bonds.

More energy is released breaking bonds than forming them (hence overall it is exothermic).
Having difficulty believing that you mean to to say this!
1
reply
CuriosityYay
Badges: 19
Rep:
?
#4
Report 1 year ago
#4
(Original post by charco)
Having difficulty believing that you mean to to say this!
He said it before: Humans make mistakes!
0
reply
liam.ro
Badges: 11
Rep:
?
#5
Report 1 year ago
#5
(Original post by Sophie.cerys)
Why do larger alkanes release more energy than shorter alkanes? As energy is required to break a bond, so as there are more bonds to break in a longer alkane, why does it release more energy?
During the complete combustion of alkanes, the C-C and C-H bonds in the alkane are broken, then O-H and C=O bonds are formed to produce water and carbon dioxide. As O-H and C=O bonds have a higher enthalpy than C-C and C-H bonds, the amount of energy released by forming bonds exceeds the amount of energy required to break bonds, making the reaction exothermic.

Hence, the larger your alkane, more potential energy can be released when the products are formed.
1
reply
Pigster
Badges: 19
Rep:
?
#6
Report 1 year ago
#6
(Original post by charco)
Having difficulty believing that you mean to to say this!
It was my daughter's fourth birthday party and I was being rushed out the door and didn't have time to check what the heck I seemed have written.

-1 marks for me.
0
reply
charco
Badges: 17
Rep:
?
#7
Report 1 year ago
#7
(Original post by Pigster)
It was my daughter's fourth birthday party and I was being rushed out the door and didn't have time to check what the heck I seemed have written.

-1 marks for me.
I have a five year old girl - I understand perfectly!
0
reply
Sophie.cerys
Badges: 13
Rep:
?
#8
Report Thread starter 1 year ago
#8
(Original post by liam.ro)
During the complete combustion of alkanes, the C-C and C-H bonds in the alkane are broken, then O-H and C=O bonds are formed to produce water and carbon dioxide. As O-H and C=O bonds have a higher enthalpy than C-C and C-H bonds, the amount of energy released by forming bonds exceeds the amount of energy required to break bonds, making the reaction exothermic.

Hence, the larger your alkane, more potential energy can be released when the products are formed.
But wouldn't the net energy released be the same? As in, larger alkanes release more energy as they break more bonds, but wouldn't they have to use more energy in bond breaking as there are more bonds to break?
0
reply
liam.ro
Badges: 11
Rep:
?
#9
Report 1 year ago
#9
(Original post by Sophie.cerys)
But wouldn't the net energy released be the same? As in, larger alkanes release more energy as they break more bonds, but wouldn't they have to use more energy in bond breaking as there are more bonds to break?
No, it cannot be constant.

Think of it this way: In a reaction where no C-C and C-H bonds are broken, and no O-H and C=O bonds are formed, the net energy released will obviously be zero. Now, when a certain amount of C-C and C-H bonds are broken, and the proportional amount of O-H and C=O bonds are formed, the net energy released will become exothermic by some constant value. If the number of C-C and C-H bonds are doubled, the proportional amount of O-H and C=O formed will be doubled, hence the energy released will also be doubled.

Simply put, since the amount of energy released for a given number of these bonds is constant, it will change linearly depending on the amount you have.
1
reply
Sophie.cerys
Badges: 13
Rep:
?
#10
Report Thread starter 1 year ago
#10
(Original post by liam.ro)
No, it cannot be constant.

Think of it this way: In a reaction where no C-C and C-H bonds are broken, and no O-H and C=O bonds are formed, the net energy released will obviously be zero. Now, when a certain amount of C-C and C-H bonds are broken, and the proportional amount of O-H and C=O bonds are formed, the net energy released will become exothermic by some constant value. If the number of C-C and C-H bonds are doubled, the proportional amount of O-H and C=O formed will be doubled, hence the energy released will also be doubled.

Simply put, since the amount of energy released for a given number of these bonds is constant, it will change linearly depending on the amount you have.
Thank you!!
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Do you have the space and resources you need to succeed in home learning?

Yes I have everything I need (73)
65.77%
I don't have everything I need (38)
34.23%

Watched Threads

View All
Latest
My Feed