Question

Define pseudo first order reaction

Answer 1

If concentration of a reactant remains constant (because it is a catalyst or because it is in great excess with respect to other reactants), its concentration can be included in rate constant thus making(causing) the reaction to be pseudo first order or sometimes pseudo second order ...
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Answer 2

the dependency of the rate of reaction on the concentration of reactants. That is if the rate is independent of the concentrations of reactants, the order of reaction is zero. Similarly, if the rate of reaction is proportional to the first power of the concentration of the reactant, then the order of reaction is one.

But sometimes the order of a reaction can be made to alter by changing the concentration of the reactants, that is, increasing or decreasing the concentration of one or the other reactant.

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