Rates and Equilibria

Question 1

How might catalysts make processes more sustainable ?

Answer 1

Catalysts not used up
Reactions take place at lower temp
Use of less fuel
Less CO emitted
Less waste

Question 2

What conditions do High pressure favour

Answer 2

A decrease in moles

Question 3

What conditions does low pressure favour

Answer 3

An increase in moles

Question 4

What conditions does an exothermic reaction favour ?

Answer 4

Lower temperature

Question 5

What conditions does an endothermic reaction favour ?

Answer 5

Increase in temperature

Question 6

How does the use of a catalyst increase rate of reaction ?

Answer 6

Lowers Ea / Provides alternate reaction pathway
Greater proportion of molecules with energy greater than or equal to the activation energy

Question 7

How would the increase in concentration of substance increase rate of reaction ?

Answer 7

More particles in a given/fixed volume
More frequent and successful collisions

Question 8

What goes on the X-Axis and Y-Axis of a boltzmann distribution ?

Answer 8

X:Axis - Energy
Y:Axis - Number of molecules

Question 9

State le Chatelier’s Principle

Answer 9

When change occurs in a closed system
Equilibrium shifts to oppose change

Question 10

Define Rate of Reaction

Answer 10

Change in concentration of a reactant pr product per unit time

Question 11

A student was asked to carry out an experiment to determine the initial rate of reaction of
zinc and hydrochloric acid.
The student plans to collect a total of about 72 cm3 of hydrogen at RTP and to use an excess of
zinc.
The student selects the following apparatus:

• the apparatus shown in the diagram
• 100 cm3measuring cylinder
• stop clock
• 2 decimal place balance
  Outline how the student could carry out the experiment and explain how the results could be
  processed graphically.
  Show all working in your calculations.

Answer 11

measure mass of
(excess) zinc (using
2 decimal place
balance)
* measure volume of
hydrochloric acid
(using measuring
cylinder)
* mix zinc and acid in
flask
* measure gas volume
at time intervals* moles of hydrogen
72/24000 = 0.00300
mol
* minimum mass of
zinc
0.003 × 65.4 = 0.20
g
* moles of hydrochloric
acid
Zn + 2HCl → ZnCl2 +
H2
0.00300 × 2 =
0.00600 mol
* volume /
concentration of acid
If [HCl(aq)] = 0.1 mol
dm-3 appropriate
volume of acid =
0.006 × 1000/0.1
= 60 cm3
If [HCl(aq)] ≥ 0.3 mol
dm-3, too low
(≤ 20 cm3)
If [HCl(aq)] ≤ 0.03
mol dm-3 too high
(≥ 200 cm3)
3. Processing results
* Plot a graph of
volume against time
* Draw a tangent at t =
0
* Gradient of tangent =
initial rate
* Gradient = volume /
time