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Calculating Rates, rate equation etc.

Hey

Ok well i am busy doing a hydrogen peroxide experiement with catalase and i am tryong to figure out the rate of the experiment by using the rate equation, i have the initial rate of reaction for my graph, but i just cant figure this out.

I know the equation for rate is:
rate = constant x [A] x
or in this case
rate = constant x [Hydrogen peroxide] x [Catalase]

The experiment was done at 17 degrees, with standard conditions.

Any help is appreciated.

Reply 1

Cynical Optimist

The rate changes throughout the reaction, so you cannot have one overall rate. What you can do, is plug in the initial rate you have found, along with the concentrations of hydrogen peroxide and catalase at the start of the experiment. You can rearrange to find the rate constant, and can then use that to find the rate for any other concentration of reactants...

Reply 2

Johans90

How would i be able to get a concentration for catalase in moldm-3 as that is the unit it needs to be in isnt it?
And how would i re-arrange it exactly to get the rate constant.

Reply 3

Cynical Optimist

Hmm, I assumed you had the catalase concentration, do you have the value in any other unit, or non at all?

Rearranging would simply be:
Constant= Rate / ([Hydrogen peroxide] x [Catalase])

Reply 4

Johans90

Im guessing the rate is the initial rate aye?
And the only value i have that may come close to the concentration of catalase is that 20g of liver is hydrogenised in 2 litres of ditilled water, but i dont know how i would be able to make that a usable concentration.

Reply 5

Cynical Optimist

That would be the initial rate, yeah. But I'm not sure what you can do to find the concentration of catalase. I guess if you knew how much catalase there is, on average, per gram of liver, you could work it out, but it would be horrible, cos you'd need it in moles and stuff. Can't imagine you have to do that - you sure you need to find different rate values? But otherwise I'm not sure, sorry.

Reply 6

Johans90

Well my investigation is to found out how different factors affect the rate of reaction with catalase, so i would have supposed so, but then technically if you say the rate is the initial rate of reaction i have technically found it out havent i?

Reply 7

Cynical Optimist

Yeah, in fact, if you have the initial rate, you can use that to compare your reactions. Seeing as the temperature was constant, I assume you changed one or both of the concentrations, and you can talk about how they are both order 1, and why higher concentrations increase the rate of reaction etc. And why temp has to be controlled.

Reply 8

Johans90

Ah got ya, thanks a lot :biggrin:

Reply 9

Cynical Optimist

No problem, good luck.

Reply 10

chemistryhelper

You cant get a rate other than the initial rate. But you can calculate a rate constant. The catalase concentration C will stay constant during the reaction because it is catalytic (ie regenerated). This means that the peroxide concentration P should decay exponentially (a pseudo-first order reaction) with an apparent rate constant, k', with units of per second. You can get this from a log plot. This parameter k' will be a product of the second order rate constant k (the constant in your equation) and the catalase concentration. You could use the mass of liver in grammes as a measure of the catalase concentration, as long as you express k in units of per second per gramme.