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Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

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Presentation on theme: "Boardworks KS3 Science 2008 Chemical Reactions (Part Two)"— Presentation transcript:

1 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

2 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

3 Energy changes in chemical reactions
Boardworks KS3 Science 2008 Chemical Reactions (Part Two) Some chemical reactions give out energy. For example: Magnesium burning – this reaction gives out heat and light energy. A candle burning – this reaction gives out heat and light energy. A battery – this reaction gives out electrical energy. Photo credit: Ramasamy Chidambaram A firework or bomb – this reaction gives out light, heat and sound energy.

4 Exothermic reactions Reactions that give out heat energy are called exothermic. Combustion is an example of an exothermic reaction – for example, when a piece of wood is burned, heat is produced. Reactions that take in heat energy are called endothermic. Sherbet dissolving on your tongue is an example of an endothermic reaction.

5 An exothermic reaction

6 An endothermic reaction

7 Endothermic or exothermic?

8 Types of chemical reactions
Boardworks KS3 Science 2008 Chemical Reactions (Part Two) There are many different types of chemical reaction. For example, oxidation is the reaction of a substance with oxygen. What is the word equation for the oxidation of copper? copper + oxygen copper oxide Reduction is the opposite of oxidation. What do you think is formed in the reduction of magnesium oxide? Chemical Reactions (Part Two) Worksheet 1 accompanies this slide. magnesium oxide magnesium + oxygen

9 Heating copper carbonate
When you heat copper carbonate, it breaks up to form copper oxide and carbon dioxide. What is the word equation for this reaction? copper carbonate copper oxide + carbon dioxide This reaction is called thermal decomposition. Can you explain why? Thermal means heat, and decomposition means breaking into smaller pieces. So in a thermal decomposition reaction, heat is used to break a substance into smaller pieces.

10 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
Combustion Boardworks KS3 Science 2008 Chemical Reactions (Part Two) A common combustion reaction is petrol burning with oxygen in a car engine. The products of this reaction are carbon dioxide and water. What is the word equation for this combustion reaction? Photo credit: © 2008 Jupiterimages Corporation petrol + oxygen carbon dioxide + water Combustion involves reacting with oxygen, so it can also be classified as another type of reaction. Which one?

11 Types of chemical reaction
Displacement reactions are commonly used to obtain pure metals from their ores. Displacement means replacing something with something else. For example, copper can be displaced from copper sulfate by reacting it with zinc. copper sulfate + zinc zinc sulfate + copper What would be displaced in the reaction between zinc sulfate and magnesium? zinc sulfate + magnesium magnesium sulfate + zinc

12 Types of chemical reaction
Boardworks KS3 Science 2008 Chemical Reactions (Part Two) What is neutralization? Neutralization is the reaction between an acid and an alkali to make a neutral substance. In the neutralization reaction between hydrochloric acid and sodium hydroxide, the products are sodium chloride and water. What is the word equation for this reaction? Photo credit: © 2008 Jupiterimages Corporation hydrochloric acid sodium hydroxide sodium chloride + + water

13 Which type of reaction?

14 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

15 Making useful gases Hydrogen, oxygen and carbon dioxide are very useful gases. Hydrogen is used to make margarine and as a rocket fuel. Oxygen is used to help things burn at a high temperature, like welding torches. Carbon dioxide is used in fire extinguishers. These gases are made in factories using chemical reactions.

16 Making and identifying hydrogen

17 Making and identifying oxygen

18 Making and identifying carbon dioxide

19 Word equations for making gases

20 Which gas?

21 Which test?

22 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

23 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
What is combustion? Boardworks KS3 Science 2008 Chemical Reactions (Part Two) Combustion is the scientific word for burning. It is the chemical reaction that takes place when a substance burns and reacts with oxygen to produce heat and light energy.

24 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
Bell jar experiment Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

25 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
The fire triangle Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

26 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
Putting out fires Boardworks KS3 Science 2008 Chemical Reactions (Part Two) If a fire starts accidentally, it is important to be able to put it out quickly and safely. To put out a fire, you can cut off the supply of any side of the fire triangle. For example: putting water on burning wood cuts off the heat. Photo credit: © 2008 Jupiterimages Corporation putting sand on burning oil cuts off the oxygen. cutting down trees in a forest fire cuts off the supply of fuel.

27 Products of combustion
Boardworks KS3 Science 2008 Chemical Reactions (Part Two) Chemical Reactions (Part Two) Worksheet 2 accompanies this slide.

28 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
Combustion of methane Boardworks KS3 Science 2008 Chemical Reactions (Part Two) Natural gas, methane, is often burned for cooking. Methane is made up of carbon and hydrogen. What gas does methane burn with? oxygen What substance will the carbon in methane change into when it burns? carbon dioxide What substance will the hydrogen in methane change into when it burns? water What is the word equation for the combustion of methane? carbon dioxide methane + oxygen + water

29 Word equations for combustion
Boardworks KS3 Science 2008 Chemical Reactions (Part Two) When substances combust, the new substances formed are called ‘oxides’. What are the word equations for these combustion reactions? 1. Coal (made from carbon) burns and forms carbon dioxide. carbon + oxygen carbon dioxide 2. Hydrogen burns and forms dihydrogen oxide (i.e water!). hydrogen + oxygen water 3. Methane burns and forms carbon dioxide and water. methane + oxygen carbon dioxide + water

30 Symbol equations for combustion
Boardworks KS3 Science 2008 Chemical Reactions (Part Two) What are the symbol equations for these combustion reactions? 1. Coal (made from carbon) burns and forms carbon dioxide. carbon + oxygen carbon dioxide C + O2 CO2 2. Hydrogen burns and forms dihydrogen oxide (i.e water!). hydrogen + oxygen water 2H2 + O2 2H2O 3. Methane burns and forms carbon dioxide and water. methane + oxygen carbon dioxide + water CH4 + + 2O2 CO2 2H2O

31 Complete and incomplete combustion
Boardworks KS3 Science 2008 Chemical Reactions (Part Two) Fuels like methane, butane and petrol are hydrocarbons. Hydrocarbons are compounds made of carbon and hydrogen. When these hydrocarbon fuels burn in a good supply of oxygen, they burn completely to make carbon dioxide and water. Photo credit: © 2008 Jupiterimages Corporation If there is a lack of oxygen, incomplete combustion takes place. This means that the fuel burns to produce water, carbon monoxide and carbon particles.

32 Incomplete combustion
Boardworks KS3 Science 2008 Chemical Reactions (Part Two) Incomplete combustion is a hazardous problem because the products of the process are toxic. Carbon monoxide prevents people’s blood from carrying oxygen. Carbon particles make city buildings very dirty, and they can get into people’s lungs and cause breathing problems. Photo credit: © 2008 Jupiterimages Corporation What precautions do you think people take in their homes to prevent incomplete combustion?

33 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
Using fossil fuels Boardworks KS3 Science 2008 Chemical Reactions (Part Two) Coal, oil and natural gas are called fossil fuels. Burning fossil fuels, like coal, petrol and natural gas, provides more than 90% of the energy we need for transport, factories and in our homes. How different would life be without fossil fuels?

34 Crude oil and fractional distillation
Boardworks KS3 Science 2008 Chemical Reactions (Part Two) The oil that comes out of the ground is called crude oil. It cannot be used as it is, because it is a mixture of many different substances with different boiling points. How can you separate a mixture of substances with different boiling points? To separate out the useful substances, a process called fractional distillation is carried out. big molecules boil at a high temperature small molecules boil at a lower temperature

35 Fractional distillation
Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

36 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
What’s the best fuel? Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

37 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

38 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
Glossary Boardworks KS3 Science 2008 Chemical Reactions (Part Two) Glossary carbon dioxide – A gas that turns limewater cloudy. combustion – The scientific word for burning, which is the reaction of a substance with oxygen. displacement – A reaction in which one element replaces another in a substance. endothermic – A reaction that takes in heat energy. exothermic – A reaction that gives out heat energy. hydrogen – A gas that makes a lighted splint produce a ’squeaky pop’. neutralization – The reaction between an acid and an alkali. oxidation – The reaction of a substance with oxygen. oxygen – A gas that relights a glowing splint. reduction – A reaction in which oxygen is removed from a substance. thermal decomposition – A reaction in which a substance is heated and breaks into smaller products.

39 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
Anagrams Boardworks KS3 Science 2008 Chemical Reactions (Part Two)

40 Boardworks KS3 Science 2008 Chemical Reactions (Part Two)
Multiple-choice quiz Boardworks KS3 Science 2008 Chemical Reactions (Part Two)


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