# Help with enthalpy

1. Feb 22, 2008

### claudzterz9

I am not sure how to find this... estimate the energy change that occurs when carbon monoxide and chlorine combine to make phosgene....

CO(g) + Cl2(g) ---> Cl2CO(g)

i have an idea of what to do,except i think its not the right way.

2. Feb 22, 2008

### AbedeuS

They do not give enthalpies of formation or Bond dissociation energies?

3. Feb 22, 2008

### lightarrow

Maybe you want to have a look to the thread " Enthalpy change and activation energy".

4. Feb 22, 2008

### uzair_kid

claudzterz9, you can do that by reacting CO and Cl2 in a calorimeter, by measuring temperatures before and after reaction.

5. Feb 22, 2008

### Kushal

take the bond energy values from your data booklet....

6. Feb 23, 2008

### lightarrow

If your problem is to estimate it from given bond energies, as Kushal wrote, then in the reaction

CO(g) + Cl2(g) ---> COCl2(g)

1. You go from a triple bond in CO to a double bond between C and O in COCl2; so you have to compute this difference of energy.
2. You loose a Cl-Cl bond and you gain 2 C-Cl bonds

So, calling E1 the energy of the triple bond between C and O, E2 the energy of double bond between C and O in phosgene, E3 the bond energy Cl-Cl and E4 the bond energy C-Cl, you have, as estimated reaction energy:

E2 - E1 + 2E4 - E3 ~ 128 kJ/mol with the data I've found (but remember there is quite variation on these kind of data).

Edit. The reaction enthalpy is the same but with sign changed.

Last edited: Feb 23, 2008
7. Feb 25, 2008

### hell-is-hot

the answer u r looking for is -100 KJ/mol..........

how i got it is by lookin at the avg bond energies for the reactants and the sum for that is 1310 and then i lloked for the the sum of the avg bond energies for the product whih is 1410.....

subtract the 2 and you get -100 kj/mol