reaction rates

Question 1

activation energy

Answer 1

the minimum amount of energy required for a successful collision to occur

Question 2

for a reaction to occur

Answer 2

• particles must collide
• particles must possess enough energy (E >= Ea)

Question 3

rate of reaction

Answer 3

total change in amount of reactant or product / time taken

Question 4

How to monitor the rate of reaction

Answer 4

• gas syringe
• measuring cylinder over water
• change in mass
• change in temp
• colour of solution

Question 5

interpreting a vol of gas produced over time graph

Answer 5

• fastest rate of reaction - most successful collision - most amount of reactant
• gradient less steep - less successful collisions
• reaction stops - no more reactant (limiting used up) no successful collisions

Question 6

factors effecting rate

Answer 6

• temp
• amount of reactants
• presence of catalysts
• surface area

Question 7

effect of concentration on rate

Answer 7

increasing conc increases rate
- more particles in the same vol
- more frequent collisions
- % of successful collisions the same
(rate and conc directly proportional)

Question 8

conc graph - excess reactant conc increased

Answer 8

• rate increases
• amount unaffected

Question 9

conc graph - limiting conc increased

Answer 9

• rate increases
• product made increases

Question 10

affect of temp on reaction rate

Answer 10

• particles gain KE and move faster
• frequency of collisions increases
• greater % of particles have E>= Ea
• greater % of successful collisions
  (rate varies exponentially with temp)

Question 11

temp graph

Answer 11

• steeper gradient (faster rate)
• total amount of gas not effected

Question 12

affect of surface are on rate

Answer 12

• smaller particle size = bigger surface area
• move surface available for reactions to take place on
• more frequent collisions

Question 13

surface area graph

Answer 13

• steeper gradient (faster rate)
• no affect on amount of CO2

Question 14

catalyst

Answer 14

speeds up the rate of reaction without being used up

Question 15

catalyse effect on rate

Answer 15

• lower Ea by providing an alternate reaction pathway
• so proportion of successful collisions with E>= Ea increases

Question 16

catalyst graph

Answer 16

• same amount of gas made
  -steeper (faster rate)

Question 17

reversible reaction

Answer 17

CuSO4. 5H2O <-> CuSO4 + 5H2O

Question 18

dynamic equilibrium

Answer 18

if there is a closed system
- forward and reverse reactions occur at same rate
- conc of reactants and products remain constant

Question 19

position of equilibrium

Answer 19

proportions of various substances in equilibrium mixture
A + B <-> C + D
- if high proportion of C moves to right
- if high proportion of B moves to left

Question 20

shifting position of equilibrium

Answer 20

if there’s a change in the system the position shifts to oppose the change
factors :
- conc
- pressure
- temp

Question 21

changing conc - on position of equilibrium

Answer 21

A + B <-> C + D
add more A - moves right
moves to side with lower conc

Question 22

changing pressure - on position fo equilibrium

Answer 22

A + 2B <-> C + D
(3 mol). (2mol)
increasing pressure shifts to side with less moles
decreasing moves to side with more moles

Question 23

implications of changing pressure

Answer 23

expensive to increase p + dangerous
slow rate of decrease p

Question 24

changing temp - on position of equilibrium

Answer 24

A + B <-> C + D
-> exo
<- endo
increasing the temp will shift in the endo direction
decreasing will shift to exo side

Question 25

implications of changing temp

Answer 25

high temp > expensive
low temp > slow rate

Question 26

adding catalyst - on position of equilibrium

Answer 26

no effect on position of equilibrium
speed up both forward and backward equally