C6 Rates

Question 1

how do you calculate the rate of reaction?

Answer 1

amount of product produced ÷ time taken

Question 2

how do you find the reaction rate from graph?

Answer 2

gradient

Question 3

describe and explain how a graph of reaction rate would look like (3)

Answer 3

1. steepest gradient = fast:
   high concentration of reactants/abundance of particles → more frequent + successful collision
2. less steep gradient = slow down:
   reactants getting used up → less collision
3. flat gradient = stops:
   all reactants used up

Question 4

We can measure the rate of a reaction by measuring…?

Answer 4

• LOSS OF MASS in certain time (gas escapes)
• collect + measure GAS PRODUCT in certain time
• TIME how long for solution to turn cloudy

Question 5

how do you collect + measure GAS PRODUCT?

use a labeled diagrams to explain (there are two ways)

Answer 5

Question 6

how do you measure LOSS OF MASS?

use a labeled diagram to explain

Answer 6

Question 7

what conditions (in terms of PARTICLES) are needed for a reaction to take place?

Answer 7

particles COLLIDE + have ENOUGH ACTIVATION ENERGY

Question 8

how do you make a reaction FASTER? (4)

Answer 8

TEMP. → move faster + more energy → more frequent + successful collision

CONCENTRATION → more particles → more frequent collision → more chance for successful collision

CATALYST → lower Ea → more particles have enough Ea → more successful collision

SA
more particle exposed → more frequent collisions → more chance for successful collision

Question 9

what do CATALYSTS do?

Answer 9

lower Ea → rxn can occur at lower temp → speed up rxn

Question 10

do catalysts get used up?

Answer 10

no

Question 11

what are the environmental benefits of using catalysts?

Answer 11

• saves energy (lower Ea)

* reduces CO2 output

Question 12

composition of air

Answer 12

78% N2
21% O2
1% CO2, argon, water vapor…

Question 13

what are some common AIR POLLUTANTS?

what are their SOURCES and EFFECTS?

Answer 13

CO

• incomplete combustion of fossil fuel
• poisonous, displaces O2 in blood

NO

• very hot environment (eg. car engines)
• acid rain

SO2

• combustion of fossil fuels that contain sulfur (eg. coal, oil, gas)
• acid rain

Question 14

how do you reduce SO2 emission?

Answer 14

• low sulfur petrol

* desulfurization by CaO

Question 15

how do you reduce CO and NO emission from car exhaust?

Answer 15

catalytic converters
• CO + O₂ → CO₂
•NO + CO → N₂ + CO₂

Question 16

why do catalysts in catalytic converters need to be replaced if they aren’t used up?

Answer 16

transition metals in converter react with lead → prevents contact of exhaust with converter

Question 17

what are NITROGEN fertilizers for?

Answer 17

protein → growth

Question 18

what are POTASSIUM fertilizers for?

Answer 18

photosynthesis → growth

Question 19

why is ammonia important in agriculture?

Answer 19

NH4NO3 fertilizer

Question 20

how does HABER PROCESS yield ammonia?

1. equation
2. conditions for optimum yield
3. where to get reactants

Answer 20

3H₂ + N₂ → 2NH₃
(balanced equation shows 3:1 ratio)

conditions:
400-450˚C, 200 atm, iron catalyst

reactants:
N2 from air
H2 from natural gas (eg.methane)

Question 21

HABER PROCESS:
why does lower temp give a higher yield of ammonia?
what is the drawback of low temp?

Answer 21

+ exothermic rxn → equilibrium towards RHS

- low temp means slower rate of rxn

Question 22

HABER PROCESS:
why does higher pressure give a higher yield of ammonia?
what is the drawback of high pressure?

Answer 22

+ equilibrium towards RHS (fewer moles)

- expensive

Question 23

what does the CONTACT PROCESS do?

Answer 23

sulfur (S) → sulfuric acid (H2SO4)

in the presence of catalyst

Question 24

what are the 4 steps of CONTACT PROCESS?

describe + equation

Answer 24

Sulfur is burnt in oxygen
S + O₂ → SO₂

Sulfur dioxide passes over catalyst (V₂O₅) in air
SO₂ + O₂ → SO₃

Sulfur trioxide dissolved in concentrated sulfuric acid
SO₃ + H₂SO₄ → H₂S₂O₇ (oleum)

Water added to oleum to make concentrated sulfuric acid
H₂S₂O₇ + H₂O → H₂SO₄