Kinetics Berkeley Review First Order Second Order...

[MCAT guy]

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So I was doing a problem and [X] was zero order and [Y] was second order rxn rate. Then they asked a question, how would the concentration of [X] drop according to time. I thought it may just be linear or something, but the answer was that [X] will drop in rct concentration in a 2nd order fashion (exponentially).

They didn't explain this idea very well in the reading.

My question is this, lets say [X] is 1st order and [Y] is 1st order. How does the concentration of [X] decrease over time? does it decrease in a 2nd order fashion (which is the overall rate), or does it decrease in a 1st order fashion (which is its own rate)?

Thx in advance!

 

[Phantastic]

My question is this, lets say [X] is 1st order and [Y] is 1st order. How does the concentration of [X] decrease over time? does it decrease in a 2nd order fashion (which is the overall rate), or does it decrease in a 1st order fashion (which is its own rate)?

If the reaction is X + Y ---> Products, then [X] should decrease at the same rate as Y, which is the rate of the reaction. Once we know the overall reaction order, that is the order of the entire reaction, and will be applicable to all reactant disappearance rates and product formation rates.

Essentially, the only thing the individual reaction orders tell you is how dependent the concentration of that reactant is on the rate. Qualitatively, [X] may not be important for the reaction rate, but it will still decrease according to the overall reaction order.

 

[MCAT guy]

If the reaction is X + Y ---> Products, then [X] should decrease at the same rate as Y, which is the rate of the reaction. Once we know the overall reaction order, that is the order of the entire reaction, and will be applicable to all reactant disappearance rates and product formation rates.

Essentially, the only thing the individual reaction orders tell you is how dependent the concentration of that reactant is on the rate. Qualitatively, [X] may not be important for the reaction rate, but it will still decrease according to the overall reaction order.

good answer, thx that clears it up bro.