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OCR Additional ScienceOCR Additional Science

Chemical EconomicsChemical EconomicsW Richards

The Weald School

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Rates of ReactionRates of Reaction

Hi. I’m Mike Marble. I’m about to have some acid poured onto me. Let’s see what happens…

Here comes an acid particle…

It missed!

Here comes another one. Look

at how slow it’s going…

No effect! It didn’t have enough

energy!

Oh no! Here comes another one and it’s got more energy…

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Rates of ReactionRates of Reaction

View animation

Chemical reactions occur when different atoms or molecules _____ with enough energy (the “________ Energy):

Basically, the more collisions we get the _______ the reaction goes. The rate at which the reaction happens depends on four things:

1) The _______ of the reactants,

2) Their concentration/pressure

3) Their surface area

4) Whether or not a _______ is used (catalysts are specific to certain reactions)

Words – activation, quicker, catalyst, temperature, collide

19/04/23Measuring the Rate of Measuring the Rate of ReactionReaction

Two common methods:

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Rate of reaction graphRate of reaction graph

Amount of product formed/ reactant used up

Time

Slower reactionFast rate

of reaction here

Slower rate of reaction here due to reactants being used

up

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Rate of reaction graphRate of reaction graph

Amount of product formed/ reactant used up

Time

Q. What if less reactants were used?

19/04/23Calculating the Rate of Calculating the Rate of ReactionReaction

Amount of product formed/ reactant used up

Time

Rate of reaction = the gradient of the graph

20cm3

10s

Rate of reaction = 2cm3/s

19/04/23Atomic massAtomic mass

SYMBOL

PROTON NUMBER = number of protons (obviously)

RELATIVE ATOMIC MASS, Ar

(“Mass number”) = number of protons + number of neutrons

19/04/23Relative formula mass, MRelative formula mass, Mrr

The relative formula mass of a compound is the relative atomic masses of all the elements in the compound added together.

E.g. water H2O:

Therefore Mr for water = 16 + (2x1) = 18

Work out Mr for the following compounds:

1) HCl

2) NaOH

3) MgCl2

4) H2SO4

5) K2CO3

H=1, Cl=35 so Mr = 36

Na=23, O=16, H=1 so Mr = 40

Mg=24, Cl=35 so Mr = 24+(2x35) = 94

H=1, S=32, O=16 so Mr = (2x1)+32+(4x16) = 98

K=39, C=12, O=16 so Mr = (2x39)+12+(3x16) = 138

Relative atomic mass of O = 16

Relative atomic mass of H = 1

19/04/23Calculating the mass of a Calculating the mass of a productproduct

E.g. what mass of magnesium oxide is produced when 60g of magnesium is burned in air?

Step 1: READ the equation:

2Mg + O2 2MgO

IGNORE the oxygen in step 2 – the question

doesn’t ask for it

Step 3: LEARN and APPLY the following 3 points:

1) 48g of Mg makes 80g of MgO

2) 1g of Mg makes 80/48 = 1.66g of MgO

3) 60g of Mg makes 1.66 x 60 = 100g of MgO

Step 2: WORK OUT the relative formula masses (Mr):

2Mg = 2 x 24 = 48 2MgO = 2 x (24+16) = 80

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Work out Mr: 2H2O = 2 x ((2x1)+16) = 36 2H2 = 2x2 = 4

1. 36g of water produces 4g of hydrogen

2. So 1g of water produces 4/36 = 0.11g of hydrogen

3. 6g of water will produce (4/36) x 6 = 0.66g of hydrogen

Mr: 2Ca = 2x40 = 80 2CaO = 2 x (40+16) = 112

80g produces 112g so 10g produces (112/80) x 10 = 14g of CaO

Mr: 2Al2O3 = 2x((2x27)+(3x16)) = 204 4Al = 4x27 = 108

204g produces 108g so 100g produces (108/204) x 100 = 52.9g of Al2O3

1) When water is electrolysed it breaks down into hydrogen and oxygen:

2H2O 2H2 + O2

What mass of hydrogen is produced by the electrolysis of 6g of water?

3) What mass of aluminium is produced from 100g of aluminium oxide?

2Al2O3 4Al + 3O2

2) What mass of calcium oxide is produced when 10g of calcium burns?

2Ca + O2 2CaO

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Percentage YieldPercentage Yield

Percentage yield = actual yield (in g)

theoretical yield

Example question:

Theoretical yield = the amount of product that should be made as calculated from the masses of atoms

Actual yield = what was actually produced in a reaction

65g of zinc reacts with 73g of hydrochloric acid and produces 102g of zinc chloride. What is the percentage

yield?

Zn + 2HCl ZnCl2 + H2

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Percentage yieldPercentage yield

Some example questions:

1)The predicted yield of an experiment to make salt was 10g. If 7g was made what is the percentage yield?

2)Dave is trying to make water. If he predicts to make 15g but only makes 2g what is the percentage yield?

3)Sarah performs an experiment and has a percentage yield of 30%. If she made 50g what was she predicted to make?

Percentage yield =

Actual yield

Predicted yieldX 100%

19/04/23Batch and Continuous Batch and Continuous processesprocesses

In summary:

Process Batch Continuous

What it means Reactants are thrown in, the reaction happens and the batch is removed

The reactants are continually fed in and the products are continually removed (e.g. the Haber Process)

Advantages Makes a wide variety of products on demand

Operate all the time and automatically, makes a large amount of product

Disadvantages More labour intensive

Can only make one product

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Developing new medicinesDeveloping new medicinesThe process:

Step 1 - research

Step 2 - development

Step 3 - legalities

Step 5 - marketing

Step 4 - manufacture

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Forms of CarbonForms of Carbon1) Diamond – very hard, doesn’t conduct electricity, very high melting point

2) Graphite – soft, does conduct electricity, very high melting point

3) Buckminsterfullerene – 60 carbon atoms arranged in a sphere

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Forms of CarbonForms of CarbonChoose a form of carbon and research the following:

1) What properties does this form of carbon have?

2) How are the electrons arranged in this structure?

3) How does the structure of this form affect its properties?

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NanoscienceNanoscienceNanoscience is a new branch of science that refers to structures built from a few hundred atoms and are 1-100nm big. They show different properties to the same materials in bulk. They also have a large surface area to volume ratio and their properties could lead to new developments in computers, building materials etc.

Task: research nanoscience and find two current and/or future applications of this science.

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Using sea waterUsing sea water

Q. Given all the problems with water shortages, why can’t we just purify sea water and use it for drinking water?

Research task: