Transcript Revision

Rates of reaction
You must revise the following:
•
•
•
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The Collision Theory
Measuring the rate of a reaction
How reaction rate is affected by:
Temperature
Concentration
Surface area and
Catalysts
Make sure you can explain each factor above
in terms of particles
Make sure you can draw and describe reaction rate graphs
The collision theory
How can rate of reaction be measured?
Measuring the rate of a reaction means measuring the change
in the amount of a reactant or the amount of a product.
What can be measured to calculate
the rate of reaction between
magnesium and hydrochloric acid?
magnesium
+
hydrochloric
acid

magnesium
chloride
+
hydrogen
Setting up rate experiments
What equipment is needed to investigate the rate?
glass tube
conical
flask
rubber connecter
rubber bung
hydrochloric
acid
magnesium
gas syringe
What can be measured to calculate the rate of reaction
between magnesium and hydrochloric acid?
magnesium
+
hydrochloric
acid

magnesium
chloride
+
hydrogen
 The amount of hydrochloric acid used up (cm3/min).
 The amount of magnesium chloride produced (g/min).
 The amount of hydrogen product (cm3/min).
Temperature
Low temperature: Particles:
• have less energy
• move slower
• collide less often
• fewer successful collisions
High temperature: Particles:
• have more energy
• move faster
• collide more often
• collide with more force
• more successful collisions
Concentration
Dilute – low concentration:
• fewer particles
• fewer collisions per second
• slower reaction
Concentration – high
• more particles
• more collisions per second
• faster reaction
Surface Area
Small surface area = big chunk
• less surface area exposed
for collisions
• fewer collisions per second
• slower reaction
Large surface area = ground/
powdered/smaller pieces
• more surface area
exposed for collisions
• more collisions per second
• faster reaction
energy (kJ)
Using a catalyst...
Ea without
catalyst
Ea with
catalyst
reaction (time)
Catalysts are chemicals that:
• Lower the activation energy...
• Speed up the reaction...
...Without being used up
Make sure you can interpret graphs showing the amount
of product formed (or reactant used up) with time, in
terms of the rate of the reaction
Rates and Graphs
Shallow gradient
Slow reaction
Steep gradient
Fast reaction
Time
Amount of reactant
Amount of product
These show the increasing amount of product
or the decreasing amount of reactant.
Steep gradient
Fast reaction
Shallow gradient
Slow reaction
Time
Calculating rate of reaction from graphs
hydrogen produced (cm3)
How can the rate of reaction be calculated from a graph?
70
60
x
50
rate of reaction = y
x
40
30
y
20
10
0
0
10
20
30
40
50
time (seconds)
The gradient of the graph is equal to the initial rate of
reaction at that time
rate of reaction = 45 cm3
rate of reaction = 2.25 cm3/s
20 s
Rates - task
• Complete the keyword and definitions
• Complete the matching statements
Quiz