What is chemical kinetics?

Chemical kinetics is the branch of chemistry that studies the speed of chemical reactions and the factors that influence them.

What are the key factors affecting the rate of a reaction?

The reaction rate depends on concentration of reactants, temperature, presence of a catalyst, and surface area of reactants.

How does chemical kinetics differ from thermodynamics?

Thermodynamics tells us whether a reaction is feasible, whereas kinetics tells us how fast it occurs

How is the rate of a reaction defined?

The rate of a reaction is the change in concentration of reactants or products per unit time.

What is the formula for the rate of disappearance of a reactant?

Rate = - Δ[R] / Δt

where Δ[R] is the change in concentration of the reactant.

What is the formula for the rate of appearance of a product?

Rate = + Δ[P] / Δt

where Δ[P] is the change in concentration of the product.

What are the units of reaction rate?

The units depend on concentration and time. For example, in terms of molarity (M):
Rate = mol L^-1 s^-1

What is the general form of the rate law?

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

How is the order of a reaction determined?

The order is determined experimentally and is not necessarily the same as the stoichiometric coefficients in the balanced equation.

What is the overall order of a reaction?

The sum of the exponents in the rate law, i.e., x + y

How does reaction order affect the rate?

• Zero order: Rate does not depend on reactant concentration.
• First order: Rate is directly proportional to reactant concentration.
• Second order: Rate depends on the square of reactant concentration.

What are the units of the rate constant k for different reaction orders?

What is the integrated rate law for a first-order reaction?

ln[A] = ln[A]₀ − kt

where [A] is the concentration at time t, [A]₀ is the initial concentration, and k is the rate constant.

How can we calculate the half-life for a first-order reaction?

t_1/2 = 0.693/k

What is the integrated rate equation for a zero-order reaction?

[A] = [A]₀ − kt

How is the rate constant determined from a first-order reaction graph?

By plotting ln [A] vs. time, the slope of the straight line gives –k.

What is the Arrhenius equation?

 k = Ae⁻ᴱᵃ/RT

where k is the rate constant, A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin.

How can the activation energy be determined graphically?

ln k = -Ea/RT + ln A
A plot of ln k vs. 1/T gives a straight line with slope = −Ea/R.

What is the role of a catalyst in a reaction?

A catalyst lowers the activation energy by providing an alternate reaction pathway.

What is the difference between homogeneous and heterogeneous catalysts?

• Homogeneous catalyst: Same phase as reactants.
• Heterogeneous catalyst: Different phase than reactants.

What is the rate-determining step?

The slowest step in a reaction mechanism, which controls the overall reaction rate.

What does collision theory state?

For a reaction to occur, molecules must:

• Collide with each other.
• Have sufficient energy (activation energy).
• Have the correct orientation.

What is the expression for the rate of reaction using collision theory?

The expression for the rate of reaction using collision theory is:
Rate = Z * e^(-Ea/RT)
where Z is the collision frequency, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin.

What is the steric factor (P) in the Arrhenius equation?

It accounts for the probability of reactants colliding in the correct orientation.

How is the half-life related to the order of a reaction?

• First-order: t_1/2=0.693/k (constant).
• Zero-order: t_1/2=[A]₀/2k (depends on initial concentration).

What is a pseudo first-order reaction?

A reaction that appears to be first-order but actually follows a higher order because one reactant is in large excess.

Give an example of a pseudo first-order reaction.

The hydrolysis of ethyl acetate in excess water:
CH₃COOCH₂CH₃+H₂O→CH₃COOH+CH₃OH
Since water is in large excess, the rate depends only on ethyl acetate concentration.

What happens to the rate if the temperature is increased by 10°C?

The rate approximately doubles.

If a reaction follows second-order kinetics and the concentration of reactant is doubled, how does the rate change?

The rate increases four times.

What is the significance of a reaction’s half-life?

It helps in predicting how long a reactant will take to reduce to half its original amount.