Reaction Rates

Question 1

what is rate of reaction

Answer 1

the change in concentration of a reaxctant or product in a given time so:

rate = change in concentration/time

Question 2

effect of increasing concentration on rate of reaction

Answer 2

- increased number of 
  particles in same volume 
- particles closer together 
  and collide more 
  frequently 
- more successful collisions 
  with enough energy to 
  overcome activation energy

Question 3

effect of increasing pressure of gas on rate of reaction

Answer 3

- same number of gas 
  molecules occupy a 
  smaller volume 
- gas molecules are closer 
  together and collide more 
  frequently 
- more successful collisions

Question 4

how to calculte rate from curve on graph

Answer 4

draw tangent at t=o (initial rate)

calculte rate from gradient of tangent

Question 5

Catalyst

Answer 5

A substance that increases the rate of a chemical reaction without being used up in the process; a catalyst provide an alternative route for the reaction with lower activation energy.

Question 6

Economical benefits of using catalysts

Answer 6

Saves energy costs as reactions can now occur in:

• lower temperatures
• low pressures

Question 7

Pollution control benefits of using catalysts

Answer 7

• Reduces CO2 emission/ greenhouse emissions

- Reduces the amount of fuel burnt

Question 8

Sustainability benefits for using catalysts

Answer 8

• Less waste produced due to higher atom economy

- reaction can take place with less toxic solvents

Question 9

How to measure rate of reaction for reactions producing gases

Answer 9

• measure volume of gas produced
• measure the loss of mass of reactants using a
  balance

Question 10

Boltzmann distribution for temperature shape

Answer 10

• At higher temperature, the peak is lower and shifted to the right
• A greater proportion of molecules can overcome the activation energy (end plateaus higher)

Question 11

explanation of boltzmann distribution for temperature

Answer 11

at higher temperature
- more molecules have energy greater than activation
energy
- greater proportion of collisions will lead to a reaction
increasing the rate of reaction
- collisions will also be more frequent as molecules are
moving faster

Question 12

Boltzmann distribution for catalysts

Answer 12

a greater proportion of molecules exceed the new lower activation energy
on collision, more molecules will react to form products

Question 13

features of an equilibrium system

Answer 13

• rate of forward reaction is equal to rate of backward
  reaction
• concentrations of products and reactants do not
  change
• closed system

Question 14

Le chateliers principle

Answer 14

when a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change

Question 15

Effect of catalyst on equilibrium

Answer 15

Catalyst does not change the position of equilibrium, only speeds up rate of forward and reverse reactions equally so speeds up rate at which equilibrium is established

Question 16

equilibrium constant (kc)

Answer 16

provides actual position of equilibrium

Question 17

kc calculation

Answer 17

kc = [products] / [reactants]

moles go outside square brackets as powers

Question 18

Meaning of kc values

Answer 18

• a kc value of 1 indicates equilibirum halfway between
  reactants and products
• kc value more than 1 indicates position of equilibrium
  towards the products
• kc value less than one indicates position of
  equilibrium towards the reactants

so larger the kc value, the further the position to the right and the greater the concentrations of products compared to reactants