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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: INeedSerotonin on November 10, 2019, 05:26:44 PM

Title: Chemical kinetics
Post by: INeedSerotonin on November 10, 2019, 05:26:44 PM

Consider the propositions below, and take into consideration that they refer to a first order unimolecular reaction.

I - the rate of reaction varies linearly with the concentration of the reagent
II - the instantaneous rate is an exponential function of time
III - the half-life of the reagent depends on its initial concentration

Which of these are correct?

Answer: (I) and (II)

I have no clue. I thought that the answer was (I) and (III).

I think that (I) is correct because V = K . [Reagents]. I have no idea why "the instantenous rate is an exponential function of time", and I swear I learnt half-life as Initial Concentration / 2^t.

Can you guys give me some hints here?

Thanks

Title: Re: Chemical kinetics
Post by: AWK on November 10, 2019, 06:11:08 PM

It's worth reading on Wikipedia about the "rate equation".

Title: Re: Chemical kinetics
Post by: mjc123 on November 11, 2019, 08:23:46 AM

Quote

I have no idea why "the instantenous rate is an exponential function of time"

What is the integrated  rate equation for a first-order reaction?

Quote

I swear I learnt half-life as Initial Concentration / 2^t.

That's nonsense; half-life is not a function of time.
Maybe what you learnt was Concentration = Initial concentration/2^(t/τ) where τ is the half-life. This is related to the answer to my first question.