It takes 42.0 min for the concentration of a reactant in a first–order reaction to drop from 0.45 m to 0.32 m at 25°c. how long will it take for the reaction to be 90% complete?

A chemical reaction in which the rate of reaction is directly proportional to the concentration of the reacting substance.

The example of the first-order reaction is as follows:-

To solve this question, the formula we are using this as follows:-

The integrated first order rate law is:

For 90% :

t =284 mins

Hence, the time required to complete 90% of the reaction is 284 mins.

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answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.