KS3 ScienceHome learning

Reactions 2

Name: _____________________________Class: _____________________________Teacher: ___________________________

In this topic you will learn about:• Exothermic and Endothermic reactions.

• How to represent energy changes in reactions.

• How to speed up reactions.

Practical skills:• Measuring temperature changes

This will prepare you for:• GCSE Chemistry

• GCSE Physics

Maths in science:• Reading a graph

• Calculating differences in temperature and energy

Lesson 1: Exothermic Reactions

Lesson 1: Exothermic Reactions

In and On:Look at the images on the board. Are the following physical or chemical changes?

1. Ice melting

2. Frying an egg

3. Burning magnesium

Challenge: What is the difference between a physical and chemical change?

Learning Objectives• Describe examples of exothermic reactions• Explain the energy changes taking place during an exothermic

reaction

What does ‘exothermic’ mean?

____________________________________________________

____________________________________________________

____________________________________________________

Exothermic reactions

Challenge: An example of an exothermic reaction is….

Energy changes occur in all ___________ ____________. Inexothermic reactions, energy is ________ _____ , usually in theform of ______. This means that the temperature of thesurroundings __________.

Exothermic reactions are reactions or processes

that release energy, usually in the form of heat or

light. In an exothermic reaction, energy is released

because the total energy of the products is less than

the total energy of the reactants.

Record your observations to identify the exothermic reaction

Explain, using ideas about particles and atoms, why burning magnesium is an exothermic reaction.________________________________________________________________________________________________________________________________________________________________________________________________________________________

Citric acid and baking soda Magnesium ribbon and Hydrochloric acid

Temperature at start (oC) 23 22

Temperature at end (oC) 10 42

Conclusion:

_______________________________________________________________________________________________________________________________________________________________

Citric Acid and Baking soda1. Add 2cm depth of citric acid to a

test tube2. Record temperature3. Add 1 spatula scoop of baking

soda4. Record temperature

Magnesium ribbon and Hydrochloric acid1. Add 2cm depth of Hydrochloric

acid to a test tube.2. Record temperature3. Add a few pieces od magnesium

ribbon4. Record temperature

Investigating exothermic reactions

How can you tell that this reaction is exothermic?____________________________________________________________________________________________________________

Burning magnesium is an exothermic reaction because when magnesium and oxygen particles collide to form new bonds, energy is released into the surroundings.

This reaction is exothermic because the energy of the

products is less than the energy of the reactants

Citric acid and baking soda is an endothermic reaction as the temperature decreases.Magnesium and hydrochloric acid is exothermic as the temperature increases.

11

the temperature increases

allow gets hotter / heat / energy is given off

(energy of) products lower than (energy of) reactants

Lesson 2 : Endothermic reactions

In and On: Using only addition, how can you add eight 8's to get the number 1,000?

Learning Outcomes:• Describe examples of endothermic reactions• Explain the energy changes taking place during an

endothermic reaction

What is the difference between endothermic and exothermic reactions?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Practical 1:1. Fill a test tube 1/3 with

Copper sulfate 2. Record the temperature3. Add a 2cm length of

magnesium ribbon4. After 1 minute, record the

temperature.Results: 5 degree temperature

increase

Practical 2:1. Fill test tube 1/3 water 2. Add 1 spatula of Sodium

Bicarb3. Record the temperature4. Add 1 spatula of Citric acid5. After 1 minute, record the

temperature.Result: 7 degree temperature decreasePractical 1

This reaction was ____________. I know this because…

Practical 2This reaction was ____________. I know this because…

__________________________________________________________________________________________________

__________________________________________________________________________________________________

888 +88 +8 +8 +8 =1,000

Endothermic reaction take in heat from their surroundings whereas exothermic reactions give out heat to their surroundings.

Exothermic as the temperature increased.

Endothermic as the temperature decreased.

Reaction Start Temp (oC) End Temp (oC) Temp Change (oC) Exo or Endo

A 22.0 33.4

B 18.6 41.7

C 24.3 19.5

D 6.1 21.7

E 22.0 -3.6

F -12.2 2.3

Endothermic reactions

1. Which type of reaction gives out energy to the surroundings?

2. Thermal decomposition is an example of …

3. Combustion is an example of…

4. Which type of reaction causes the temp of the surroundings to decrease?

5. An Ice pack is an example of…

Endothermic or Exothermic?

How can you tell this reaction is endothermic?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

This reaction is endothermic because the energy of the products is more than the energy than the

reactants. Energy has been taken in.

✓

use a polystyrene cup

better insulator

✓

✓

21.4

15.8 16.1

Lesson 3: Investigating endothermic ReactionsIn and On: Is this reaction endothermic or exothermic?________________________________________________________________________

Challenge: How do you know?_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

1. Measure out 10 cm3 of water using a measuring cylinder. Record the starting temperature of the water in your results table

2. Collect a polystyrene cup with a pre weighed amount of potassium chloride in it. Record the mass to the appropriate number of decimal places in the table.

3. Add the water to your cup. Record the lowest temperature shown on your thermometer and record this answer to the appropriate number of decimal places.

4. Calculate the change in temperature.

Method:

What are the variables for this experiment?Independent____________________________________________________________Dependant______________________________________________________________Control_________________________________________________________________

Mass of potassiumchloride (g)

Start temperature(oC)

End temperature(oC)

Change in temperature(oC)

2 24 22 2

4 24 20 4

6 24 18 6

8 24 16 8

10 24 14 10

Independent – Mass of potassium chloride (g)Dependent – TemperatureControl – Volume of water, same polystyrene cup, length of time

Drawing graphs

• Independent variable always goes on the x axis (horizontal)

• Dependent variable always goes on the y axis (vertical)

• Remove any anomalous results

• Ensure you have a title

• Ensure you have labelled each axis and state the unit

• Ensure gaps are uniform ie. Every square is equal to 2 degrees Celsius

• Draw a line of best (either with a ruler or a curve –do NOT join the points)

Conclusion:

___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Challenge:Why did you use a polystyrene cup rather than a beaker? ______________________________________________________________________________________________________________________________________________

How could you improve the experiment to make your results more reliable?_____________________________________________________________________________________________________________________________________________________________________________________________________________________

Additional notes:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

The more marble chips added to the acid, the greater the temperature increase. This is an exothermic reaction.

The polystyrene cup provides greater insulation than a beaker.

Carry out the experiment 3 times and take an average of your results.

Lesson 4: Catalysts https://www.youtube.com/watch?v=-4HXaUBbv04

Lesson 4: CatalystsIn and On: Which road would you choose and why?________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________

Road 1

Road 2

1. What are the 4 factors affecting the rate of reaction?

2. What is the activation energy?

3. What does the rate of a reaction depend on?1.2.

4. Why does the rate of reaction increase with increased temperature?

5. Why are catalysts not included in reaction equations?

6. How do catalysts speed up the rate of reaction?

7. Give 2 examples of catalysts

Additional notes:_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

What is rate of reaction?______________________________________________________________________________________________________________________________

Learning Objectives:

• To describe what a catalyst is• Explain how catalysts work

Road 2 as it is a straighter road meaning that you will get to your destination quicker.

Different reactions go at different speeds. We call the time taken for a reaction to complete the rate of reaction.

Which graph shows a reaction with a catalyst? Explain your answer._________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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: Graph 2 as there is a lower activation energy than in graph 1.

Haber Process

Making ammonia from nitrogen and hydrogen.

Reactions 2 Catalysts

Nitrogen + Hydrogen → Ammonia

N2 (g) + 3 H2 (g) → 2 NH3 (g)

An iron catalyst is used to speed up the rate of this reaction.

Making Margarine

Vegetable oils are ‘hardened’ using hydrogen gas.

This type of reaction is known as hydrogenation.

Example:Ethene + Hydrogen → Ethane

A nickel catalyst is used to speed up the rate of this reaction.

Reactions 2 Catalysts

Making

Sulfuric Acid

Reactions 2 Catalysts

A three step reaction. The catalyst is needed in step 2.

Step 1: Sulfur + Oxygen → Sulfur dioxideStep 2: Sulfur Dioxide + Oxygen → Sulfur TrioxideStep 3: Water + Sulfur Trioxide → Sulfuric Acid

A Vanadium Oxide catalyst is used to speed up the rate of this reaction.

Catalytic Converters in CarsThey convert harmful emissions into less harmful substances.

Carbon monoxide + Oxygen → Carbon dioxide2 CO (g) + O2 (g) → 2 CO2 (g)

Carbon monoxide + Nitrogen monoxide → Carbon dioxide + Nitrogen2 CO (g) + 2 NO (g) → 2CO2 (g) + N2 (g)

Hydrocarbons + Nitrogen monoxide → Carbon dioxide + Nitrogen + Water

Rhodium, Palladium and Platinum can be used as a surface for the catalytic converter.

Reactions 2 Catalysts

Oxygen Sulfur trioxide

increases

activation

catalyst or increase temperature

Lesson 5: Combustion https://www.youtube.com/watch?v=cRnpKjHpFyg

Label the reactants and products for the following reaction:

Challenge: Write this as a symbol equation:

Lesson 5: Combustion

In and On: match the reaction to its definition

Extension: how are hand warmers an example of an exothermic reaction?________________________________________________________________________________________________________________________________________________

Physical reaction

Physical properties of a substance changes but no new substances are made

Chemical reaction

Chemical reaction where energy is taken in

Exothermic reaction

Chemical reaction where energy is given out

Endothermic reaction

One or more substances are changed into others by rearranging their atoms

Learning Objectives:• Summarise combustion using an equation • Make observations during chemical reactions• Write word equations to represent chemical equations

Methane + Oxygen → Carbon dioxide + Water

When a fuel burns, chemical energy is transferred into heat ___________. Wood, coal, petrol and gas are all examples of ___________. Burning is a _________ reaction. The scientific name for burning is _______________.

When a fuel burns, it reacts with ____________ in the air to form carbon dioxide and ______________. The reaction also gives out ______________ energy.

CH4 + O2 → CO2 + H2O

Can you light a candle on the moon? Explain your answer.______________________________________________________________________________________________________________________________

You can not light a candle on the moon because there is no oxygen gas

Label the reactants and products for the following reaction:

Write this as a symbol equation:

CH4 + O2 → CO2 + H2 O +

What is the difference between complete and incomplete combustion?______________________________________________________________________________________________________________________________

Describe why burning is a chemical reaction______________________________________________________________________________________________________________________________Explain why a fire will burn more brightly is you fan the flames with air______________________________________________________________________________________________________________________________Describe the problems associated with the production of carbon dioxide______________________________________________________________________________________________________________________________ChallengeExplain why combustion is also known as an oxidation reaction______________________________________________________________________________________________________________________________

Additional notes:_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

When a fuel undergoes complete combustion, it releases the maximum

amount of energy from the fuel being reacted. Incomplete combustion is

also a reaction between oxygen and fuel but the products are carbon monoxide, water and carbon

• used up in burningaccept ‘oxygen burned’do not accept ‘used up’• it reacted with fuel or petrol• formed carbon dioxide or carbon monoxide

water

It is poisonous or toxic

Lesson 8: Explaining changes

Lesson 8: Explaining changes

In & On:What would be the mass of the salt solution? Explain your answer.

Law of conservation of mass____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

What is physical change?____________________________________________________________________________________________________________________________ ______________________________________________________________ ____________________________________________________________________________________________________________________________

Learning Objectives:

• Observe and explain mass changes for chemical and physical processes• Use particle diagrams to explain chemical processes

Mass of water: 250gMass of salt = 5g

If 6g of calcium reacts with 2g of oxygen, what mass of calcium oxide will form?

If 12g of calcium oxide forms from 9g of calcium, what mass of oxygen has reacted?

Examples: Calcium + Oxygen → Calcium oxide

255g

No new products are made, the process is reversible

e.g. freezing water or melting ice

The Law of Conservation of Mass

No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.

8g

3g

Magnesium and Magnesium Oxide are both solids at room temperature. Oxygen is a gas.Predict – what would appear to happen to mass when they react?_____________________________________________________________ _____________________________________________________________ _____________________________________________________________

Burning Magnesium

Describe and Explain what appears to happen to mass when magnesium and oxygen react. _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________Challenge:Describe and Explain what appears to happen to mass during the thermal decomposition of copper carbonate._____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________

Total mass of reactants = Total mass of products

If one of the reactants is a gas, mass can appear to ________________

If one of the products is a gas, mass can appear to ________________

10.00g50.00g

54.00.00g

5.00g9.00g

I predict that the mass will increase as Mg bonds with the oxygen in the air.

The mass increases as Mg bonds with oxygen in the air forming magnesium oxide (white powder).

Mass appears to decrease. When copper carbonate decomposes, carbon dioxide is formed, which is a gas, and escapes from the boiling tube, therefore is not accounted for when weighing products.

Use the state symbols to predict whether mass would APPEAR to increase or decrease in the reactions. Use full sentences.

______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________

______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________

CaCO3 (s) → CaO (s) + CO2 (g)

4 K (s) + O2 (g)→ 2 K2O (s)

Additional notes________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Decrease as carbon dioxide is a gas and it would escape from the container (beaker).

Increase as potassium bonds with oxygen from the air to form magnesium oxide.

B

D

a compound or a new substance has been formed

oxygen

carbon dioxide

the same numbers of each type of atom are present

RevisionThe next 2 pages are left blank for you to use for revision in preparation for the end of topic test.Your teacher may ask you to complete a specific revision activity or ask you to revise independently.Suggested activities include: Mind maps, practice questions from the text book, flash cards, memorising key words and concepts.Use this booklet to help you, revision guides and the internet.