Chemical Kinetics

Question 1

What is Chemical Kinetics?

Answer 1

Chemical Kinetics is the branch of chemistry which deals with the study of rates of chemical reactions and the mechanism by which the reactions proceed.

Question 2

Explain Elementary and Complex Reactions.

Answer 2

Elementary reactions take place in one step while Complex reactions take place in the sequence of elementary reactions (several steps).

Question 3

What is the Rate of Chemical Reaction?

Answer 3

The change in concentration of reactants or products per unit time.
(SC) -Δ[R]/Δt = (SC) +Δ[P]/Δt
If stoichiometry coefficients are the same then we put them as they are but if not then we put them in their inverse form.

Question 4

What are the Units of Rate of Reaction?

Answer 4

Units of rate of Reaction is mol/Ls but for gaseous reactions it is atm/s.

Question 5

What is the Average & Instantaneous Rate?

Answer 5

Average Rate is the rate of change of concentration per unit of time & Instantaneous Rate is the change in a very small interval w.r.t very small interval of time.
rₐᵥ = -Δ[R]/Δt = +Δ[P]/Δt
rᵢₙₛₜ = -d[R]/dt = +d[P]/dt

Question 6

How is Rate of a Reaction determined on a graph?

Answer 6

Determination of instantaneous rate is done by drawing a tangent at time t on either of the curves, and making it graph of concentration of reactant vs time or concentration of product vs time.

Question 7

What are the factors which influence the Rate of a Reaction?

Answer 7

1) Concentration
2) Temperature
3) Catalyst
4) Surface area of the reactants
5) Presence of radiation

Question 8

What is Rate Law?

Answer 8

The representation of the rate of reaction in terms of molar concentration of one or more reactants is called rate law.
Rate = k[A]ˣ [B]ʸ
Here, A & B are the concentrations, k is the rate constant and ˣ & ʸ are the exponents determined experimentally.

Question 9

What are the characteristics of Rate Constant?

Answer 9

1) Greater the value of rate constant, faster the reaction.
2) Every reaction and temperature has a definite value of rate constant.
3) It does not depend on the concentration of reactants.
4) It depends upon the order of the reaction.

Question 10

What is the Order of Reaction?

Answer 10

The sum of the powers of the concentration of the reactants in the rate law expression is called the order of the chemical reaction.
k = (mol L⁻¹)¹⁻ⁿs⁻¹

Question 11

What is the Molecularity of a Reaction?

Answer 11

The number of reacting species taking part in an elementary reaction must collide simultaneously to bring about a chemical reaction.

Question 12

What is the Rate-Determining Step?

Answer 12

The slowest step in a reaction will be the determining step.

Question 13

What are Zero-Order Reactions?

Answer 13

The rate of reaction has a power of zero in this the rate does not depend on the concentration of any reaction.
Equation: k = [R]₀ - [R] / t

Question 14

What are First-Order Reactions?

Answer 14

The rate of reaction is proportional to the first power of the concentration of the reactant, R.
k = 2.303/t log a/(a-x)

Question 15

What is the expression for the Rate Constant at t₁ and t₂?

Answer 15

k = 2.303/ t₂ - t₁ log [R]₁/[R]₂

Question 16

What’s the Half-Life of a Reaction?

Answer 16

The time in which the concentration of a reaction gets reduced to one-half of its initial concentration.
For zero orders,
tₒ.₅ = [R]₀/2k
For first orders,
tₒ.₅ = 0.693/k
For nᵗʰ orders,
tₒ.₅ = 1/[R]₀ⁿ⁻¹

Question 17

What are Pseudo First Order Reactions?

Answer 17

Reactions which are not actually first order reactions but behave so due to altered conditions.

Question 18

What is the Arrhenius Equation?

Answer 18

log k₂/k₁ = eₐ/2.303R [T₂ - T₁/T₁T₂]

Question 19

What is Activation Energy?

Answer 19

The energy required to convert the reactants into an unstable intermediate before they eventually form a compound is called activation energy.

Question 20

What is the most probable kinetic energy?

Answer 20

The kinetic energy possessed by most of the molecules in a reaction

Question 21

What is a catalyst?

Answer 21

A substance which alters the rate of reaction without itself undergoing any chemical change.

Question 22

What is the Collision Theory of chemical reactions?

Answer 22

Activation energy and proper orientation of molecules together determine the criteria for an effective collision and thus, the rate of reaction.