You are Here: Home

# Calculating unknown bond enthalpies watch

1. Please could somebody help me with an explanation of how to work out this question. Been trying for ages and I can't get the same answer as the text book...

Attachment 617144617146

The only data relevant in table 1 is the O=O avg. bond enthalpy being 498kj per mol.

Thanks
Attached Images

2. (Original post by nathanjeffs)
Please could somebody help me with an explanation of how to work out this question. Been trying for ages and I can't get the same answer as the text book...

Attachment 617144617146

The only data relevant in table 1 is the O=O avg. bond enthalpy being 498kj per mol.

Thanks
Bond breaking in the reactants is positive (endothermic) and bond formation in the products is negative (exothermic).

You have all of the bond enthalpies, do the sums.
3. (Original post by charco)
Bond breaking in the reactants is positive (endothermic) and bond formation in the products is negative (exothermic).

You have all of the bond enthalpies, do the sums.
Thanks for your help. Like I said I have attempted the sums, this being as far as I got...

Bonds broken: 4 x S=O bonds, 1 x O=O (enthalpy 498kj/mol)
Bonds formed: 6 x S=O bonds

Enthalpy change = energy to break bonds - energy to form bonds = -192kj/mol

so: (4 x S=O + 498) - 6 x S=O = -192kj/mol

-2 S=O = -690kj/mol giving me an average bond enthalpy of 345kj/mol where the actual answer is 469kj/mol. So if anybody could please give me the correct method to solve this it would be much appreciated.
4. (Original post by nathanjeffs)
Thanks for your help. Like I said I have attempted the sums, this being as far as I got...

Bonds broken: 4 x S=O bonds, 1 x O=O (enthalpy 498kj/mol)
Bonds formed: 6 x S=O bonds

Enthalpy change = energy to break bonds - energy to form bonds = -192kj/mol

so: (4 x S=O + 498) - 6 x S=O = -192kj/mol

-2 S=O = -690kj/mol giving me an average bond enthalpy of 345kj/mol where the actual answer is 469kj/mol. So if anybody could please give me the correct method to solve this it would be much appreciated.

### Related university courses

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: February 4, 2017
The home of Results and Clearing

### 1,268

people online now

### 1,567,000

students helped last year
Today on TSR

### IT'S TODAY!

A-level results chat here

### University open days

1. London Metropolitan University
Sat, 18 Aug '18
2. Edge Hill University
Sat, 18 Aug '18
3. Bournemouth University