Topic 7

Question 1

7.1
Devise an experiment to investigate the effect of concentration
on the rate of reaction

Answer 1

a) -10cm³ sodium thiosulfate (w/ measuring cylinder) into conical flask
-10cm³ HCl to same cf
-Cf on black cross
-Record t taken (w/ stop clock) for ╳ to disappear
-Repeat w/ diff concs sodium thiosulfate
-Repeat whole experi & work out mean for each conc

Question 2

7.1
Devise an experiment to investigate the effect of temperature on the rate of reaction [3 marks]

Answer 2

-Water bath to heat solution to desired temp
-Record (w/ stop clock) t for colour change to occur -> obscure cross
-Repeat w/ diff temps
-Ensure same v of solution used each t

Question 3

7.1
Devise an experiment to investigate the effect of using small vs large marble chips on the rate of reaction

Answer 3

-Fixed v (measuring cylinder) HCl in conical flask
-Fixed m (balance) SMALL marble chips in flask
-Stopper flask w/ bung + delivery tube
-Delivery tube into trough filled w/ water
-Upturned measuring cylinder over tube
-H₂ gas trapped in cylinder
-Measure gas v every 30 secs
-Continue until no more H₂ produced
-Repeat w/ same mass LARGE marble chips

Question 4

7.1 7.3
State 4 ways the rate of reaction can be increased

Answer 4

-↑ temp
-↑ pressure
-↑ conc
-Catalyst

Question 5

7.2
Suggest 4 methods of determining the rate of reaction

Answer 5

-Collection of gas w/ gas syringe
-Collection of gas over water
-Monitor change in mass of gas (gas mass change)
-Monitor colour change

Question 6

7.2
What does the reaction between calcium carbonate and hydrochloric acid produce?

Answer 6

Calcium chloride + Water + Carbon dioxide

Question 7

7.2
What does the reaction between magnesium and hydrochloric acid produce?

Answer 7

Magnesium chloride + Hydrogen gas

Question 8

7.2
The change in the mass of a gas is monitored by placing marble chips into a solution of hydrochloric acid. The top is sealed with cotton wool. Explain what would happen to the reading on the balance

Answer 8

-↓
-CO₂ can escape

Question 9

7.3
Why do most reactions slow down overtime

Answer 9

Reactants are used up

Question 10

7.3
What is a successful collision?

Answer 10

Produces reaction

Question 11

7.3
Suggest a way you could monitor the rate of reaction over time during a practical

Answer 11

Use gas syringe
(measures change in v)

Question 12

7.4
Explain the effect of increasing temperature on the rate of reaction

Answer 12

-Gain KE -> faster
-↑ frequent, successful collisions
-r. reaction ↑

Question 13

7.4
Explain the effect of increasing concentration on the rate of reaction

Answer 13

-↑ particles closer together in same given v
-↑ frequent successful collisions
-r. reaction ↑

Question 14

7.4
Explain the effect of increasing pressure on the rate of reaction

Answer 14

-Less space -> closer together
-↑ frequent successful collisions
-r. reaction ↑

Question 15

7.4
Explain the effect of increasing surface area on the rate of reaction

Answer 15

-↑ particles exposed to reactant
-↑ frequent successful collisions
-↑ r. reaction

Question 16

7.5
State the equation used to calculate the rate of reaction

Answer 16

r. reaction = change in amount of reac or prod/time

(usually the gradient)

Question 17

7.6
Define the term catalyst

Answer 17

-Speeds up r. reaction
-W/o altering products
-Its m remains unchanged

Question 18

7.6
Why are catalysts useful in industry?

Answer 18

-↓activation E
-Allow reactions to occur at ↓ temp + pressure
-↓ E cost required to ↑ temp + pressure

Question 19

7.6
Platinum is a very expensive catalyst. Suggest why this does not matter

Answer 19

Not used up -> can be re-used

Question 20

7.7
Describe how catalysts increase the rate of reaction

Answer 20

-Provide alternate pathway
-W/ lower activation E

(Note: doesn’t increase frequency of collisions. Increases frequency of successful collisions bc particles have greater activation E)

Question 21

7.7
Explain why catalysts in catalytic converters in car exhausts are spread onto a honeycomb structure rather than used as large pieces

Answer 21

-↑ SA
-↑ successful frequent collisions
-↑ r. reaction

Question 22

7.7
Explain why catalysts are more effective when the engine has been running for a short time rather than when the engine is first started

Answer 22

-Catalyst heats up
-Reaction faster as particles have more KE so move faster

Question 23

7.8
What is an enzyme? What is one use they have?

Answer 23

-Biological catalyst
-Speeds up r. reaction

-Produce alcoholic drinks

Question 24

7.8
Compare biological and chemical catalysts

Answer 24

-Both lower activation E -> speed r. reaction

-Bio: Specific to certain reactions, denatured by heat/pH
-Chemical: More resistant to heat/pH

Question 25

7.9
a) Name 4 chemical reactions that experience a change in heat energy (energy transferred to or from the surroundings)
b) How can the heat change be measured?

Answer 25

a) -Salt dissolve in water
-Neutralisation
-Displacement
-Precipitation
b) Thermometer

Question 26

7.10
What is an exothermic reaction?

Answer 26

Heat E given out

Question 27

7.11
What is an endothermic reaction?

Answer 27

Heat E taken in

Question 28

7.12
What type of reaction (endo or exo) is
a) making bonds
b) breaking bonds

Answer 28

a) exo
b) endo

Question 29

7.13
When will the overall heat energy change for a reaction be exothermic? When will it be endothermic?

Answer 29

Exo
-↑ heat E released when forming bonds than breaking
Endo
-↑ heat E released when breaking bonds than forming

Question 30

7.14
Calculate the energy change when hydrogen and chlorine react to form hydrogen chloride
H-H + Cl-Cl -> 2H-Cl
State whether the reaction is exothermic or endothermic

Bond energies:
H-H = 436 kJ mol-¹
Cl-Cl = 243 kJ mol-¹
H-Cl = 432 kJ mol-¹

Answer 30

H-H
1 × 436 = 436
Cl-Cl
1× 243 = 243
Total E in (bonds broken) = 679

2H-Cl
2 × 432 = 864
Total E out (bonds made) = 864

E change = E in - E out
= 679 - 864
= -185 kJ mol -¹

Exothermic (bc negative sign)

Question 31

7.15
Define the term activation energy

Answer 31

Min amount of E required for reaction to occur

Question 32

State the formula for calcium carbonate

Answer 32

CaCO₃