For a first-order reaction, the half-life is constant. it depends only on the rate constant and not on the reactant concentration. it is expressed as: t1/2=0.693/k

for a second-order reaction, the half-life depends on the rate constant and the concentration of the reactant and so is expressed as: t1/2= 1/k[a]0
a. a certain first-order reaction (a--> products) has a rate constant of 3.30×10^-3 s^-1 at 45 degrees c. how many minutes does it take for the concentration of the reactant, [a], to drop to 6.25% of the original concentration?
b. a certain second-order reaction (b--> products) has a rate constant of 1.70×10^-3 m^-1*s^-1 at 27 degrees c and an initial half-life of 296 s. what is the concentration of the reactant b after one half-life?

A.  14 min

B . 0.995 M

Explanation:

A.

Using integrated rate law for first order kinetics as:

Where,  

is the concentration at time t

is the initial concentration

Given:

The final concentration is dropped to 6.25 % of the initial concentration. SO,

= 0.0625

k =

So,

Also, 1 s = 1/60 minutes.

So,

14 minutes it takes for the concentration of the reactant to drop to 6.25% of the original concentration.

B.

(a) Half life expression for second order kinetic is:

Where,  

is the initial concentration = ?

k is the rate constant = M⁻¹s⁻¹

Half life = 296 s

So,

Half life is the time at which the concentration of the reactant reduced to half. So, concentration remains = = 0.995 M

hurricanes form when warm, moist air from the ocean surface quickly rises into the atmosphere and forms storm clouds and rain. when the clouds are formed, heat is released which warms the cool air in the upper regions of the atmosphere so that the cycle can continue. which two phases of the water cycle are repeated in this process?