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