kinetics

Question 1

what must particles do in order to react ?

Answer 1

• collide with sufficient energy (activation energy) and the correct orientation.

Question 2

define activation energy.

Answer 2

• the minimum energy that particles much collide with for a chemical reaction to occur

Question 3

what does the rate of a chemical reaction depend on?

Answer 3

• how often the reactant particles are colliding
• how many of those collisions are successful .

Question 4

what’s the effect of increasing temperature on rate of reaction? why?

Answer 4

• increasing temp —> increased rate of reaction as particles move faster
• much higher proportion of particles have energy greater than activation energy —> many more successful collisions per second —> increased rate of reaction

Question 5

what is the effect of increasing concentration/pressure on rate of reaction? why?

Answer 5

• increased conc/pressure —> increased rate of reaction.
• more reactant particles in a given volume thus more frequent successful collisions —> increased rate .

Question 6

what is a catalyst?

Answer 6

• a substance which increases the rate of reaction but is not used up in the reaction.

Question 7

how do catalysts work and how do they increase the rate of reaction?

Answer 7

• reduce the activation energy for reaction so more particles have energy.
• dropping energy barrier —> provides an alternative reaction pathway

more particles will have sufficient energy to react so there’s more successful collision which increase rate of reaction

Question 8

how does surface area increase the rate of reaction?

Answer 8

• increased SA of solid reactant means that more particles will be exposed, so more frequent collisions.

Question 9

how do you calculate the reaction rate ?

Answer 9

• change in mass of reactant of product
  ————————————————————
  time
• from a graph = calculate gradient - steeper gradient , the faster the rate or reaction.

Question 10

what are homogeneous catalysts ?

Answer 10

• which are in same state as reactants (is reactants all aq then homogenous catalysts also aq)
• forming an intermediate —> reactants will react with catalyst to form intermediate —> reform catalyst

Question 11

what are heterogeneous catalysts ?

Answer 11

-diff state/phase to reactants (e.g - using solid catalyst to catalyse reaction between gases)

• SA of catalyst may act as limiting factor for rate of reaction

Question 12

what are the benefits of using catalysts ?

Answer 12

• used to make industrial processes cheaper and faster
• less fuel needs to be burned and less CO2 is emitted making reaction more sustainable .
• reduce waste by providing an alternative reaction pathway with a higher atom economy .
• haber process used finely divided iron catalyst to provide surface for nitrogen and hydrogen to react to form ammonia