Learning Objectives:

• State what rate of reaction is
• Identify observable changes to reactants or products for determining the rate of reaction
• Dtermine average rate of reaction
• Determine average rate of reaction at any given time from a graph
• Solve numerical problems involving average rate of reaction
• Solve numerical problems involving rate of reaction at any given time

The rate of reaction is the speed at which the reactants are converted into products in a chemical reaction.

• The amount of reactants decreases
• The amount of products increases

• Volume of gas liberated
• Time taken for precipitate formed
• Change of mass during reaction
• Color, temperature or pressure change

Solved Example: 9168-02

Rate constant for first order reaction is 6.93 $\times$ 10$^{-3}$s$^{-1}$. The half life of the reaction will be:

A. 10 s

B. 1000 s

C. 1 s

D. 100 s

Correct Answer: D

Solved Example: 9168-03

The rate of a chemical reaction doubles for every 10$^\circ$C rise of temperature. If the temperature is raised by 60$^\circ$C , then the rate of reaction increases by:

A. 10 times

B. 24 times

C. 64 times

D. 32 times

Correct Answer: C

Solved Example: 9168-04

For the reaction system \[2 NO(g) + O_2(g) \rightarrow 2NO_2 (g)\] the volume is suddenly reduced to half its value by increasing the pressure on it. lf the reaction is first order with respect to O$_2$, and second order with respect to NO, the rate of reaction will

A. Increase to four times of its initial value

B. Decrease to one-fourth of its initial value

C. Decrease to one-sight of its initial value

D. Increase to eight times of its initial value

Correct Answer: D

Learning Objectives:

• Understand the concept of reaction order in chemical kinetics, which quantifies the relationship between reactant concentrations and the rate of a chemical reaction.
• Understand experimental methods for determining the reaction order, including the method of initial rates, isolation of a variable, and graphical analysis.

Reaction Order: The number of reacting molecules whose concentration alters as a result of chemical change is called the order of reaction” OR “The sum of exponents in the rate expression of a reaction is the order of reaction” OR “The power to which concentration of reactant is to be raised to get the rate of reaction”.

• First order reaction
• Second order reaction
• zero order reaction

• If a reaction rate depends on a single reactant and the value of the exponent is one, then the reaction is said to be first order.
• $r = k [A]$

• The rate of reaction is directly proportional to the square of the concentration of one of the reactants.
• $r = k [A]^2$

• For a zero-order reaction, the rate of reaction is a constant. When the limiting reactant is completely consumed, the reaction abrupt stops.
• $r = k$

Solved Example: 9168-01

In a batch reactor a homogenous reaction R → P occurs. The conversion of reactant R is 67% after to minutes and 80% after 20 minutes. Find the order of reaction up to nearest integer.

A. 1

B. 1.5

C. 2

D. 0

Correct Answer: C