This set of Chemistry Quiz for Class 12 focuses on “Collision Theory of Chemical Reactions”.
1. When a catalyst is involved in the collision between the reactant molecules, more energy is required.
Explanation: When a catalyst is involved in a collision between the reactant molecules, less energy is required for the chemical reaction to take place. Catalyst brings down the activation energy of the overall chemical reactions and the reaction takes place at a lower energy state.
2. Which of the following explains the increase in the reaction rate by a catalyst?
a) Catalyst decreases the rate of backward reaction so that rate of forward reaction increases
b) Catalyst provides extra energy to reacting molecules so that they produce effective collisions
c) Catalyst provides an alternative path of lower activation energy to the reactants
d) Catalyst increases the number of collisions between the reacting molecules.
Explanation: It is because when the activation energy (Ea) is lower in a reaction, more number of reactant particles have enough energy to react and form products. Hence, it provides an alternative path and the reactions tend to occur faster.
3. Effective collisions are those in which molecules must acquire the energy of activation.
Explanation: For the collisions to be effective, molecules must collide with sufficient energy, known as activation energy so that chemical bonds can break. This causes the reaction to occur faster and to form the required products.
4. Who put forward the collision theory of chemical reactions?
a) Trautz and Lewis
b) Luigi Galvani
c) Henry Cavendish
d) Alessandro Volta
Explanation: In 1916, Max Trautz and William Lewis put forward the collision theory giving a better explanation about the rates of reactions. According to this theory, it is assumed that the reactant molecules are hard spheres and reaction between them occurs only when they collide with each other.
5. The proper orientation of reactant molecules leads to bond formation.
Explanation: Proper orientation of reactant molecules leads to bond formation because improper orientation makes the reactant molecules bounce back and hence the reaction won’t take place and the required products will not to be formed.
6. Which of the following is a drawback of collision theory?
a) Proper orientation
b) High activation energy
c) Hard spheres
d) Have energy equal to or greater than the threshold energy
Explanation: In Collision theory, activation energy and proper orientation of molecules together determine the criteria for an effective collision but it has a certain drawback as it considers atoms/molecules to be hard spheres and ignores their spherical aspects.
7. What is the term used to refer to the number of collisions per unit volume of the reaction mixture?
a) Collision force
b) Collision frequency
c) Collision energy
d) Collision time period
Explanation: The number of collisions per unit volume of the reaction mixture is known as collision frequency. According to this theory, the reactant molecules are assumed to be hard spheres and reaction is postulated to occur when molecules collide with each other.
8. What is the rate of reaction for a bimolecular elementary reaction?
a) ZAB e-Ea/RT
b) ZAB eEa/RT
c) – ZAB e-Ea/RT
d) – ZAB eEa/RT
Explanation: The rate of reaction is equal to the product of collision frequency of reactants and the fraction of molecules whose energies are equal to or greater than that of the energy of activation. Where ZAB represents collision frequency of reactants, A and B and e-Ea/RT represents a fraction of molecules with energies equal to or greater than E.
9. In a chemical reaction, if the reactant requires a high amount of activation energy, then what is the behaviour of the reaction?
d) Doesn’t depend on activation energy
Explanation: The reaction occurs slowly only if the reactants are slow, so if the reactants are slow we have to provide a high amount of Activation energy (Ea) to the reactants. This enhances the speed of the reactants in the reaction and to form products.
10. What are the factors that determine an effective collision?
a) Translational collision and energy of activation
b) Threshold energy and proper orientation
c) Proper orientation and steric bulk of the molecule
d) Collision frequency, threshold energy and proper orientation
Explanation: The factors that determine an effective collision are:
Collision frequency: The number of collisions per unit volume of the reaction mixture is known as collision frequency.
Threshold energy: Threshold energy is the minimum kinetic energy the molecules must have to bring about effective collisions between two reactant molecules considered as hard spheres, resulting in a chemical reaction. Proper orientation.
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