kinetics

Question 1

define: activation energy

Answer 1

the minimum amount of kinetic energy particles must collide with to break existing bonds in the reactant particles and start a reaction

Question 2

draw the reaction profile for an exothermic reaction

Answer 2

pic

Question 3

draw the reaction profile for an endothermic reaction

Answer 3

pic

Question 4

what do the maxwell-boltzmann distribution curves show?

Answer 4

the distribution of the energies of the particles in a gas

Question 5

what are the four main about the maxwell-boltzmann distribution curves to note?

Answer 5

• there are no particles with zero energy
• the curve does not touch the x-axis at the higher end
• the area under the curve is equal to the number of particles in the system
• the peak of the curve indicates the most probable energy of any particle

Question 6

what particles can react when a collision occurs?

Answer 6

only the particles with energy equal to or greater than the activation energy

Question 7

in this picture, which temperature is higher?

pic

Answer 7

T2

Question 8

how does temperature affect the rate of reaction?

Answer 8

at higher temperatures, particles move faster and

therefore there is a large increase in the number of particles with higher kinetic energies

which results in a large increase in the rate as there will be more frequent successful collisions

Question 9

why does even a small increase in temperature increase the rate?

Answer 9

because there are a greater number of particles with energy greater than the activation energy

Question 10

what effect does concentration have on the rate of reaction?

Answer 10

increasing the concentration of reactants in a solution will result in particles being closer together

and so there will be more frequent collisions and more chances for particles to react

Question 11

what effect does increasing the pressure of gaseous particles have on the rate?

Answer 11

increasing the pressure will result in the gas particles being closer together

and so there are more frequent successful collisions

and so a faster rate of reaction

Question 12

define: catalyst

Answer 12

a substance that alters the rate of a chemical reaction but is unchanged itself at the end of a reaction

does not get used up

Question 13

how do catalysts work?

Answer 13

by providing an alternative reaction pathway that has a lower activation energy

Question 14

does a catalyst alter the maxwell-boltzmann distribution curve?

Answer 14

no

Question 15

what affect does catalysts have on the proportion of particles?

Answer 15

because it provides a route with a lower activation energy,

there will be a greater proportion of particles with greater energy than the activation energy

Question 16

why are catalysts useful?

Answer 16

because a catalyst increases the rate of reaction without being used up its cheaper than increasing the temperature or concentration

Question 17

what happens if the frequency of collisions is increased?

Answer 17

the rate of reaction will increase

Question 18

what can be done to increase the frequency of collisions

Answer 18

by increasing:
- the concentration of the reactants in solution
- the temperature
- the surface area of a solid reactant
- the presence of a catalyst

Question 19

what does increasing the concentration of a solution do to the rate?

Answer 19

increasing the concentration of a solution increases the number of reactant particles per unit volume

and so increases the probability of productive collisions between reactive particles

this change increases the reaction rate

Question 20

what does increasing the pressure of a gaseous reactant to to the rate?

Answer 20

if the pressure of a gas is increased, the particles in the gas are pushed closer together

this increases the concentration of the gas

and so the rate of collisions is increased

Question 21

what does increasing the surface area of a solid reactant do to the rate?

Answer 21

if more surface is exposed then there is a greater surface area available for collisions

and so a faster rate of reaction

Question 22

what does increasing the temperature of the reaction do to the rate?

Answer 22

particles have more energy at higher temperatures

so they move about more quickly

and so there are more frequent successful collisions

and so a faster rate of reaction