Question about simple kinetics and stoichiometry

Gold Member
Hi, I'm having trouble with this simple reaction (1):

$$A + A → I$$

with ##R = kC^2_A##

I'm assuming it takes place in a Batch reactor so the mass balance should yield:

$$\frac {dC_A} {dt} = -2R = -2kC^2_A$$

But, as I recall (I should be wrong though), stoichiometry in thermodynamics and kinetics is just "math": it does not have any "physical" meaning (unlike in chemistry), but it only serves to assure mass is conserved during the reaction.

So I can re-write reaction (1) like:

$$A → \frac 1 2 I$$

But now:

$$\frac {dC_A} {dt} = -R = -kC^2_A$$

What am I missing ?

mfb
Mentor
Your k will depend on how you write the reaction.

dRic2
What am I missing ?
The rate equation is given for a specific chemical equation. That means A+A→I and A → ½ I have different rate equations.

dRic2
Gold Member
That makes a lot of sense! Thank you very much :)

DrDu