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Iodine and Propanone Activation Enthalpy

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enthalpy change of formation has to be negative, as energy is given out as the bonds are formed, if no bonds are broken no energy is used.

so /\HF has to be negative

Reply 21

2^1/2

but earlier in the question, you asked for activation energy, this is entirely different and must be positive!

so we needs to know the overall equation, and you are unlikely to find these in a databook (Ea values)

Reply 22

2^1/2

*stars and stripes*

The activation energy value for the reaction between iodine and propanone, pretty please?

Hi just to let you know, (see my previous posts) you ask for the activation energy and you have been told the enthalpy change of formation, which will have the wrong sign and the wrong value.

It is unlikely that you will be able to find Ea in a standard data book, as it would be impossible to list every single reaction.

Reply 23

*stars and stripes*

Doh! Oh deary, deary me, this is what you get when Danielle is away with the fairies :redface:

You're right, of course! Thank you for pointing this out, you saved me from writing something very silly in my coursework :smile:

Rep for you too!

Reply 24

2^1/2

many thanks, i didn't want you to make a silly mistake, sort of thing i do all the time.

Reply 25

*stars and stripes*

It's what you get after having 2-3 hours sleep the night before, ah the perils of being a student :wink:

Reply 26

Kyalimers

Indeed 2^1/2 is correct however having just mentioned this is for your coursework, YOU DON'T GET Ea values for reactions anywhere, even on the net. There's just so many reactions

\Delta H_f

is used instead to show the energy that would be required to from that product. Its much simpler!!! For Ea values you'll need the Data Book that Oxford have in their vast library. Its one of very very few that have millions of Ea values listed in them. I personally would still use

\Delta H_f

Reply 27

*stars and stripes*

Thanks for the tip and explanation :smile:

I can't really trek to Oxford otherwise :wink:

Reply 28

Kyalimers

Having just done 2 hrs of searching I still come up with nothing - but this:

THE Arrhenius Equation

Unparseable latex formula:

k=Ae^{\frac{-E_A}{RT}

Reply 29

Kyalimers

where: k is the rate constant

E_A

is the activation energy

T is the temp. in Kelvins

R is the gas constant (8.31J K^-1 mol^-1)

A is approximately constant

e is 2.71828....

Reply 30

Kyalimers

lol - try using that if you really do need the Activation Energy Value, if not use

\Delta H_f

Reply 31

Kyalimers

I don't want to leave you for dead which is why I keep returning here for you lol!!!

Reply 32

*stars and stripes*

That's really sweet, thank you :smile:

Can't believe you spent two hours looking for me!

I feel really bad, but I've used the Arrhenius equation already, as I calculated my own value for the activation enthalpy...I just wanted to compare it to a known value to see how accurate mine was!