Question

Explain the first order reaction and second order reaction with example​

Answer 1

hi friends........

At first, let’s talk about rate law expression…

The rate at which a reaction goes on is defined by its rate law expression. It relates the concentration of the reactants at time t to the reaction rate at that moment(If you put the concentration in the expression, it will give you the rate, simple!).

For equation, 2A + 3B → 4C + 5D

The rate law expression is:

r=k[A]^x [B]^y

where k is rate constant, x,y are reaction orders that are to be determined experimentally but maybe equal to stoichiometric coefficients i.e. maybe x=2 and y=3(only sometimes!)…

The sum of x and y is called order of the reaction.

Now, 1ST ORDER REACTION is one where

1. the rate r depends only on the concentration of one reactant(there maybe other but their reaction order must be zero, see examples below…)

2. the order of the reaction must be one.

In reaction, A + 2B → C

r=k[A]^1 [B]^0

As the reaction order for B is zero so r is independent of [B] and therefore rate law expression can be written as:

r=k[A]^1

Again if

r=k[A]^1/2 [B]^1/2 is also not a 1st order reaction as the order (x+y) may be equal to 1 but it depends on the concentration of B too which violates rule 1.

And

r=k[A]^2 is not a 1st order as the order of the reaction is not equal to 1…

FOR EXAMPLE, nitrogen-tetroxyde falling apart into 2 nitrogen-dioxydes.

The speed of the reaction only depends on the concentration of the reactant hence why it is first-order

A SECOND ORDER REACTION is a type of chemical reaction that depends on the concentrations of one second order reactants or on two first order reactants.

You can determine the second order reaction by sieng it’s SI Unit that is L/mol/sec.

hope it helps.......

Answer 2

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