Aims
Class work
21 September 2007
How fast?
LO’s
• Do all reactions go at the same speed?
Write it down!!
© C Meyer
Page 58
What have I learnt?
•
You have 15 mins to complete Q1-3
What have
I learnt?
What have I
learnt?
What have I learnt?
Chemistry Unit 2 Sections
Rates of Energy and
Acids, alkalis
reaction  reactions  Electrolysis  and salts
4 of 7
© C Meyer
Aims
All
• Know that reactions go at different
speeds and they can be measured
Most
• Define rate of reaction
• List different measurement
techniques
Some
• Explain why a certain method is best
to use to measure reaction rates
Do all reactions go at the same speed?
•
Rate of reaction is just another way
of saying how fast is the reaction
1. Give me the fastest and slowest
reaction you can think of
2. Give me a biological reaction, is it
fast or slow?
Do all reactions go at the same speed?
Fast
Explosions
Fireworks
Slow
Metal rusting
Do all reactions go at the same speed?
Do all reactions go at the same speed?
•
In a lab chemical reaction, what 2 ways could
we measure how fast the reaction is going?
Two common ways:
1) Measure how fast the
products are formed
2) Measure how fast the
reactants are used up
Do all reactions go at the same speed?
Title – Rate of reaction
• Can measure how fast reactants used up
or products are made
What different ways could we do this with
the following reaction?
calcium
carbonate
+ hydrochloric
acid
 calcium
chloride
+ water
+ carbon
dioxide
CaCO3(s) + 2HCl(aq)  CaCl2(aq) + H2O(l) + CO2(g)
What state are chemicals in?
Use mass
of chemical
(solid, liquid, gas)
Use volume
of chemical m3
Do all reactions go at the same speed?
SAFETY
20 mins
Acid - Goggles
Need 2 graphs at the end
What measurements will you take?
Do all reactions go at the same speed?
SAFETY
20 mins
Acid - Goggles
Time
0s
Reading
??g
60
Time
0s
Reading
0 cm3
120
As the gas given off leaves
the flask the total mass of
the flask and its contents
decreases slightly.
The gas given off can
be collected in a
syringe and readings
taken every 30
Readings of the mass(g) can
seconds or so.
be taken. Typically at 1
Need 2 graphs at the end
minute intervals.
Tidy UP!!!
•
•
•
•
Stack items tidily
Clean up bench/floor
Sit down when finished
Draw your graphs
Homework
•
Finish off drawing your graphs and
label what is going on
Do all reactions go at the same speed?
Rate of reaction graph
Amount of
product
formed
Slower rate of reaction here
due to reactants being used up
Fast rate
of reaction
here
Dependent v independent??
Slower reaction
Time
Rate graphs and reactant concentrations
Amount of product
All product
Mix of reactant
And product
Reactant Concentration falls
Rate of Reaction falls
Gradient of graph decreases
All reactant
Time
Do all reactions go at the same speed?
Demo – precipitation
• If the product is a precipitate there
is a third method you can use.
+ hydrochloric  sodium + water + sulphur + sulphur
Sodium
acid
thiosulphate
chloride
dioxide
Na2S2O3(aq)
+ 2HCl(aq) 
2NaCl(aq) + H2O(l) + SO2(g) + S(s)
We can how long it takes to
produce enough sulphur to make
the solution opaque (non seethrough).
If cross disappears quickly,
is the reaction fast or slow?
The End