Flashcards for NEET Chemistry - Chemical Kinetics

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Chemistry

Chemical Kinetics

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Chemical Kinetics

Order of a Reaction

It is the sum of powers of the concentration of the reactants

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

order = x + y

Zero-Order Reactions

Rate = k[R]⁰

k = [R]₀−[R]/t

unit of k is mol L^-1s^-1

E.g. The decomposition of gaseous ammonia on a hot platinum surface

The thermal decomposition of HI on gold surface

First-Order Reactions

Rate = k[R]

k = 2.303/t log [R]₀/[R]

unit of k is s^-1

E.g. All natural and artificial radioactive decay of unstable nuclei, decomposition of N₂O₅ and N₂O

Half-Life of a Reaction

It is the time in which the concentration of a reactant becomes half of its initial concentration. It is denoted by t_1/2.

For zero order reaction t_1/2 ∝ [R]₀ or initial concentration

t_1/2 = [R]₀/2k

For first order reaction t_1/2 is independent of [R]₀ and is equal to 0.693/k

Collision Frequency

It is the number of collisions per second per unit volume

Rate of reaction = Z_AB e^{−Ea /RT}

Z_AB – collision frequency of reactants

e^{−Ea /RT} – fraction of molecules with energies equal or more than Ea (activation energy)

Arrhenius Equation

It explains the temperature dependence of the rate of a reaction

k = A e^{-Ea /RT}

A – Arrhenius factor or the frequency factor

Ea – activation energy in joules/mole (J mol ^–1)

Pseudo First Order Reaction

Reactions that become first order under certain conditions

E.g. Acid hydrolysis of ethyl acetate

Acid catalysed inversion of cane sugar

Effective Collisions

Collisions in which molecules collide with sufficient kinetic energy or threshold energy and proper orientation

Rate = P_ZAB e^–Ea/RT

P – probability or steric factor

Activation Energy (E_a)

It is the energy required by reactant molecules to form the intermediate or activated complex (C)

ΔH = Activation energy of forward reaction – Activation energy of backward reaction

Also check:

• NEET Chemistry Syllabus
• NEET Chemistry Important Topics
• NEET Chemistry MCQs
• How to Score 160 Plus in NEET Chemistry