Kinetics

Question 1

Rate of Reaction Definition

Answer 1

the change in concentration of a particular reactant/product per unit time

Question 2

Activation Energy Definition

Answer 2

the minimum amount of energy required for a reaction to occur
or
the minimum energy that colliding molecules need in order to have successful collisions leading to a reaction

Question 3

How is rate constant affected by temperature?

Answer 3

as the temperature increases so does the rate constant

Question 4

Ways in which rate of reaction can be measured

Answer 4

volume of gas produced
change in mass
change on transmission of light (colorimetry)
change in concentration using titration
change in concentration using conductivity
‘clock reactions’

Question 5

Two factors needed for reaction to take place between two reactant particles

Answer 5

• they must collide with the correct geometry so that the reacting parts of each particle come into contact with each other (stearic effect)
• the reactants must collide with sufficient kinetic energy in order to overcome the activation energy

Question 6

Temperature effect on Rate of Reaction

Answer 6

increase temp, increase Ek, increase in collision frequency due to higher Ek
also increase in frequency of collisions involving particles with the necessary activation energy
so increase in successful collisions
so increase in Rate of Reaction

Question 7

Concentration effect on Rate of Reaction

Answer 7

concentration increases, frequency of collisions increases
therefore frequency of sucessul collisions increases
and so Rate of Reaction increases

Question 8

Particle Size effect on Rate of Reaction

Answer 8

decreasing particle size, increases total surface area
allows more contact and higher probability of collisions between reactants
therefore increase in Rate of Reaction

Question 9

Pressure effect on Rate of Reaction (gases only)

Answer 9

compressing the gas (essentially increases concentration)
increases frequency of collisions
increasing Rate of Reaction

Question 10

Catalyst effect on Rate of Reaction

Answer 10

a catalyst works by providing an alternate reactive pathway for the reaction that has a lower activation energy
this increases the Rate of Reaction without themselves being permanently chemically changed during the reaction

Question 11

Units of k for overall order of reactions

Answer 11

zero order: mol dm^-3 s^-1
first order: s^-1
second order: mol^-1 dm^3 s^-1
third order: mol^-2 dm^6 s^-1

Question 12

Graphs for zero order reactions

Answer 12

concentration-time: straight line (negative grad) gradient = k
rate - concentration: horizontal line

Question 13

Graphs for first order reaction

Answer 13

concentration-time: curve showing rate decreasing with concentration
rate - concentration: straight line passing through origin with grad=k

Question 14

Graphs for second order reactions

Answer 14

concentration-time: also a curve but steeper at the start and levelling off more
rate - concentration: positive parabola

Question 15

Reaction Mechanism Definition

Answer 15

the pathway by which a reaction occurs or the sequence of elementary steps that leads to product formation
or
a proposed pathway of how a reaction might take place

Question 16

Reaction Intermediates

Answer 16

species that appear in the mechanism but not in the overall balanced equation

Question 17

Transition state of a reaction

Answer 17

halfway between reactants and products (top of curve)

Question 18

Rate constant relationship to A

Answer 18

directly proportional to therefore to frequency and orientation of collisions

Question 19

Rate constant relationship to Activation Energy

Answer 19

decreases with increasing activation energy