Answer to Question #104022 in General Chemistry for mya

Question

A particular reactant decomposes with a half‑life of 111s when its initial concentration is 0.366M.

The same reactant decomposes with a half‑life of 231s when its initial concentration is 0.176M.

Determine the reaction order.

What is the value and units of the rate constant for this reaction?

Answer 1

To know the order of reactions, one must know the equations of the reactions rate constants.

1. For the first-order reaction: k₁=0.693/t_1/2 , where t_1/2 - half-life. Rate constants of the same reaction has to be the same, but when its initial concentration is 0.366M then k₁=0.0062 , and when its initial concentration is 0.176M then k₁=0.003. In conclusion, this is't first-order reaction.
2. For the second-order reactions: k₂=1/(t_1/2*C₀) , where C₀ - initial concentration.

k₂=1/(111*0.366)=0.0246 M ^-1 s ^-1

k₂=1/(231*0.176)=0.0246 M ^-1 s ^-1

So, this reaction of decomposition of a particular reactant is a second-order reaction, and its rate constant is: k₂=0.0246 M ^-1 s ^-1