chapter five_reaction kinetics

Question 1

three requirements or conditions for a reaction to take place

Answer 1

1. collide
2. collide with sufficient energy to overcome activation energy
3. be in the correct orientation

Question 2

what happens if these conditions are not met?

Answer 2

the molecules will bounce off each other

Question 3

what affects the ROR?

Answer 3

the proportion of particles that overcome the activation energy. the lower the AE the higher the ROR

and

the frequency that effective collisions occur.

Question 4

what is the definition of: ROR

Answer 4

ROR: the change in the concentration of a product or a reactant over time.

Question 5

what determines that a reaction is first, second or zeroth order? (check against notes)

Answer 5

when the rate is directly proportional to [A], the reaction is first order.

when the rate is directly proportional to [A}^2, the reaction is second order. i.e., when [A] doubles, the ROR x4.

when the rate is unaffected, the reaction is zeroth order.
when the change in the concentration of one reactant doesn’t affect the ROR, the reaction is zeroth order wrt that reactant.

Question 6

what do the graphs of zero, first and second order look like?

Answer 6

zeroth: straight line (constant gradient).
first: curve, with a constant half-life.
second: similar shape to the first order, but with no constant half-life.

Question 7

what are the factors affecting ROR?

Answer 7

1. changes to pressure (GAS ONLY). the higher the pressure the higher the ROR.
   the reactants are closer to one another, hence the frequency of collisions and hence effective collisions increases. hence ROR increases.
2. surface area. the larger the surface area, the high there ROR.
   the larger the surface area that comes into contact with the reactant, the larger the frequency of effective Collins and hence ROR.
3. effect of temperature. the higher the temp, the higher the ROR
   the main effect is that now a larger proportion of particles have enough energy to overcome the activation energy barrier and hence more ec occurs.
4. presence of catalysts.
   it lowers the activation energy.

Question 8

heterogenous catalysts:

define adsorption and desorption processes.

Answer 8

adsorption: the particles diffuse towards the surface of the catalyst, and is adsorbed into the active sites of the catalyst. they form weak forces of attraction. hence, the particles are brought closer to one another and are in the correct orientation for reaction to occur.
desorption: the PRODUCT molecules then diffuse away from the surface of the catalyst and the active sites are ready to adsorb new REACTANT molecules