Aims
Class work 21 September 2007
How fast?LO’s• Do all reactions go at the same speed?
Write it down!! Page 58© C Meyer
• You have 15 mins to complete Q1-3
What have I learnt?
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
All• Know that reactions go at different
speeds and they can be measuredMost• Define rate of reaction• List different measurement
techniquesSome• Explain why a certain method is
best to use to measure reaction rates
Aims
• 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?
Do all reactions go at the same speed?
Fast
ExplosionsFireworks
Slow
Metal rusting
Do all reactions go at the same speed?
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?• In a lab chemical reaction, what 2 ways
could we measure how fast the reaction is going?
Title – Rate of reaction• Can measure how fast reactants used
up or products are made
Do all reactions go at the same speed?
m3
What different ways could we do this withthe 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?
(solid, liquid, gas) Use volumeof chemical
Use massof chemical
SAFETYAcid - Goggles
20 mins
Do all reactions go at the same speed?
Need 2 graphs at the end
What measurements will you take?
SAFETYAcid - Goggles
20 mins
Do all reactions go at the same speed?
As the gas given off leaves the flask the total mass of the flask and its contents decreases slightly.
Readings of the mass(g) can be taken. Typically at 1 minute intervals.
The gas given off can be collected in a syringe and readings taken every 30 seconds or so.
Time Reading
0 s 0 cm3
Time Reading
0 s ??g
60
120
Need 2 graphs at the end
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
Rate of reaction graphAmount of product formed
Time
Slower reactionFast rate
of reaction here
Slower rate of reaction here due to reactants being used
up
Do all reactions go at the same speed?
Dependent v independent??
Rate graphs and reactant concentrationsA
mou
nt o
f pr
oduc
t
Time
reactants
product
Reactant Concentration falls
Rate of Reaction falls
All product
All reactant
Mix of reactant
And product
Gradient of graph decreases
Demo – precipitation• If the product is a precipitate there
is a third method you can use.
Do all reactions go at the same speed?
Sodium thiosulphate
+ hydrochloric acid
sodium chloride
+ water + sulphur dioxide
+ sulphur
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 see-through).
If cross disappears quickly,is the reaction fast or slow?
The End
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