You are Here: Home

# Enthalpy change of reaction Watch

1. So, for (a) I did:

And then

So: Energy release:

I have no idea what to do for (c)!
BTW: Part (b) was just asking me to draw an enthalpy profile diagram.
Anybody give me some guidance?
2. (Original post by halpme)

So, for (a) I did:

And then

So: Energy release:

I have no idea what to do for (c)!
BTW: Part (b) was just asking me to draw an enthalpy profile diagram.
Anybody give me some guidance?
The answer to part (a) would be positive 681kJ because its asking how much energy is released so it's positive. It would be negative if it asked for the enthalpy change.
And for part (c) you're going to kick yourself when I tell you...
Spoiler:
Show
It's the same value as the original enthalpy change of reaction, but the opposite sign, so +49kJ
3. (Original post by sam1w2e)
The answer to part (a) would be positive 681kJ because its asking how much energy is released so it's positive. It would be negative if it asked for the enthalpy change.
And for part (c) you're going to kick yourself when I tell you...
Spoiler:
Show
It's the same value as the original enthalpy change of reaction, but the opposite sign, so +49kJ
. Without sound like a 4 year old... Why?
4. (Original post by halpme)
. Without sound like a 4 year old... Why?
Well it's the same for any equilibrium reaction, one reaction is essentially the reverse of the other.
So for example: if you were to carry out a reaction which was endothermic, if you were to carry out the reverse reaction, in order to get back to the original reactants you would have to release the same amount of energy as was taken in from the forward reaction. So the magnitude of the enthalpy change of the forward and reverse reaction are the same, but opposite signs.
I hope that helped
5. (Original post by sam1w2e)
Well it's the same for any equilibrium reaction, one reaction is essentially the reverse of the other.
So for example: if you were to carry out a reaction which was endothermic, if you were to carry out the reverse reaction, in order to get back to the original reactants you would have to release the same amount of energy as was taken in from the forward reaction. So the magnitude of the enthalpy change of the forward and reverse reaction are the same, but opposite signs.
I hope that helped
But it says energy released there: that means that bonds are being made and therefore energy is being released which makes , right? Or is but ?

EDIT: I think what I'm asking is how do I find out which reaction is endothermic/exothermic?
Surely the forward reaction is exothermic because here is my answer to (b): Is that incorrect?

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: August 18, 2013
Today on TSR

### Oxford interview invitations

When is yours coming?

### Highest poster before midnight WINS £30!

Discussions on TSR

• Latest
• ## 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.

• Poll
Discussions on TSR

• Latest
• ## 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.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.