Task for the week commencing: 20/04/2020 due 24/04/2020

Print or write the question and answer on a document that you can submit. Answers should be in your own words (not copied andpasted). Attempt to write an answer without using any other resources (textbook, exercise book or internet).

Assessment

The symbol equation below shows the reaction when methane burns in oxygen.

CH4 + 2O2 → CO2 + 2H2O

An energy level diagram for this reaction is shown below.

2. Explain the significance of x, y and z on the energy level diagram in terms of the energy transfers which occur when these chemical bonds are broken and formed.

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(Total 9 marks)

1. Which chemical bonds are broken and which are formed during this reaction?

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KS4 SCIENCE SUCCESS CRITERIA1. Read the notes in your exercises book the night before

each science lesson.

2. Review the topic being studied on BBC Bitesize for 10 minutes the night before each lesson.

3. On Saturday - Use a science text book/ BBC Bitesize and make your own revision cards for the topic being studied.

4. On Sunday – Read and learn the information on each revision card for the topic being studied.

What is a reaction profile?DO NOW

Define activation energy.

Copy the reaction profile for endothermic and expthermicreactions.

CHEMISTRY TOPIC 5 – ENERGY CHANGES

Reaction Profiles

Learning Objectives

Use reaction profiles to identify

reactions as exothermic or endothermic.

Draw simple reaction profiles

(energy level diagrams) for

exothermic and endothermic.

BRIDGES – Making Connections

Starter

true

true

false

false

true

false

CHEMISTRY TOPIC 5 – ENERGY CHANGES

Reaction Profiles

Learning Objectives

Use reaction profiles to identify

reactions as exothermic or endothermic.

Draw simple reaction profiles

(energy level diagrams) for

exothermic and endothermic.

BRIDGES – Making Connections

Main•Exothermic means “Heat out” Heat is given out to the surroundings•Endothermic means “Heat in” Heat is taken in from the surroundings•All reactions are either exothermic or endothermic.

SOME REACTIONS ARE OBVIOUSLY EXOTHERMICe.g. methane gas burning is exothermic as there is a flame that is hot.e.g. The reaction between magnesium and copper oxide is an exothermic reaction because there is a temperature rise.HOWEVER it isn’t quite as simple as this.All reactions are in fact a mixture of exo and endo processes.If we say a reaction is exothermic, then what this really means is that the exopart of the reaction is greater than the endo part of the reactionWhen we say a reaction is exothermic what we are really saying is that the overall

reaction is exothermic.When we say a reaction is endothermic what we are really saying is that the overall

reaction is endothermic.

Extra explanationImagine an example using money instead of energy.Imagine you are investing money into an investment fund in a bank.We will show the results of the investment over time on a graph.

On the graph: paying in money shown by direction & payback money shown by direction

Money in fund

Time

Would this be a good investment?

Money

in fund

Time

Paid in

Paid back

This is a good investment because you have more “payback” than “pay in”

Money

in fund

Time

£5,000 £7,000

Take an actual example. How much money would you make on this deal?

Answer = £2,000

The profit is the difference between the two arrows

Money

in fund

Time

£5,000 £3,500

A MEMBER OF STAFF ACTUALLY MADE AN INVESTMENT WHICH COULD BE REPRESENTED BY THS GRAPH.

How did he feel about this?

Overall £5,000 paid in and £3,500 paid back

So overall loss, or drop of £1,500

What if you made more than oneinvestment at the same time?Imagine you invest £ 5,000 and £4,000Imagine the paybacks are £2,000 and £8,000

How do you feel – was this a good deal?

OR

Total investment = £5,000 + £4,000 = £9,000Total payback = £2,000 + £8,000 = £10,000

So

Back to Chemistry- Energy instead of Money

In chemistry the “paying in” part of reactions is breaking bonds between atoms. e.g. breaking up hydrogen molecules

Breaking bonds always involves a “paying in” of energy and is represented by an direction on the energy graph. We call this an investment of energy

H H H H

1 molecule 2 separate atoms

In chemistry the “paying back” part of reactions is making bonds between atoms. e.g. the making of a hydrogen molecule from two hydrogen atoms

H H H H

1 molecule2 separate atoms

This is shown by a direction on an energy graph

Let’s now apply this to an actual example

Magnesium reacts with iron oxide to make magnesium oxide and iron

Mg + FeO = MgO + Fe

Mg Fe O FeOMg

This bond must break This bond must be madeThis involves “pay in”of energy

This involves a “pay back”of energy

On an energy graph this will look like:

Energy

Time

Energy “PAY IN” to break the FeO bond

Energy “PAY BACK” on making the MgO bond

Mg + FeO = MgO + Fe

More “PAY BACK” energy than “PAY IN” energy – this is a GOOD energy deal.A “GOOD” energy deal is Exothermic

Energy

Time

Mg + FeO = MgO + Fe

This is the ENDO’ part of the reaction

This is the EXO’ part of the reaction

We say this is an exothermic reaction (overall) since the exothermic part is greater than the endothermic part

Working out the overall energy change

The overall energy change is given by the difference between the lengths of the two arrows

The overall energy change is In exam questions, you will be given energy values so that you can work out the lengths of the arrows

330kJ/mole 400kJ/mole

70kJ/mole

70kJ/mole

Energy

Time

What sort of reaction would have this energy graph and why?

This sort of reaction would be ……………………… because the energy ………………. for …………………… bonds is …………… than the energy ………………… from ……………………… bonds.

The ………………………………………. part of the reaction is greater than the ……………………………………. part.

Assessment

endothermic absorbedbreaking greater released making

endothermicexothermic

Exothermic reactions - a summary

Energy

Progress of reaction

ReactantsProducts

Activation energy

In exothermic reactions the energy of the reactants is greater than the energy of the products

The activation energy is the minimum energy required to break the bonds and start the reaction off

Endothermic reactions - a summary

Energy

Progress of reaction

Reactants

ProductsActivation energy

In endothermic reactions the energy of the products is greater than the energy of the reactants

The activation energy is the minimum energy required to break the bonds and start the reaction off

Plenary Copy and complete.Mark and correct in green pen.

CHEMISTRY TOPIC 5 – ENERGY CHANGES

Reaction Profiles

Learning Objectives

Use reaction profiles to identify

reactions as exothermic or endothermic.

Draw simple reaction profiles

(energy level diagrams) for

exothermic and endothermic.

BRIDGES – Making Connections

Exothermic reactions and catalysts

Energy

Progress of reaction

ReactantsProducts

A.E. without cat

A.E. with catalyst

A catalyst lowers the activation energy. This helps the bonds to break more easily so the reaction works faster at that temperature.NOTE that the overall energy change is the SAME

Add notes to your diagram.

How would a catalyst change the energy graph of an endothermic reactions?

Energy

Progress of reaction

Reactants

Products

A. E. no cat

A.E. with catalyst

Again the reaction would go faster because the activation energy has been lowered

Again note that the overall energy change is the same

Add notes to your diagram.

CHEMISTRY TOPIC 5 – ENERGY CHANGES

Reaction Profiles

Learning Objectives

Use reaction profiles to identify

reactions as exothermic or endothermic.

Draw simple reaction profiles

(energy level diagrams) for

exothermic and endothermic.

BRIDGES – Making Connections

Mark off areas of the topic cob=vered at the end of each lesson.

Required Practical - Distinguish between exothermic and endothermic reactions on the basis of the temperature change of the surroundings.

Required Practical - Evaluate uses and applications of exothermic and endothermic reactions given appropriate information.

Draw simple reaction profiles (energy level diagrams) for exothermic and endothermic reactions showing the relative energies of reactants and products, the activation energy and the overall energy change, with a curved arrow to show the energy as the reaction proceeds.Use reaction profiles to identify reactions as exothermic or endothermic.Explain that the activation energy is the energy needed for a reaction to occur.(HT) Be able to calculate the energy transferred in chemical reactions using bond energies supplied.