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1. Create a mind map that outlines the differences between decomposition, synthesis, single replacement reactions and double replacement reactions, giving an example of each type.

�. The reaction below could be described as being a double replacement reaction.

AgNO3 + NaCl → AgCl + NaNO3

Explain why it has this label. �. The chemical reaction described by the following

equation could be called a decomposition reaction. CuSO4 → CuO + SO3

Using this case as an example, explain what is meant by the term decomposition reaction.

4. A weak acid, carbonic acid (H2CO3), is present in soft drinks. This decomposes to give two products, one of which is CO2—the bubbles in the soft drink that give it its fizz. What is the other product? Write a balanced decomposition equation for this reaction.

5. The expression ‘in the limelight’ comes from the days of theatre before electricity. In those days, powdered limestone (calcium carbonate) was heated strongly until it decomposed into two products, one of which was CO2. The other product, lime, glowed while it was heated, and this ‘limelight’ was directed onto stage by means of mirrors. What is the chemical formula of calcium carbonate? What about that of lime? What is the equation for the decomposition reaction that is occurring?

�. It is sometimes useful to write general equations for the different types of reactions. For example, synthesis reactions can be described as:

A + B → AB Write general equations for double replacement,

single replacement and decomposition reactions. 7 . Figure 1.28 shows the reaction between an iron

nail and a solution of copper sulfate. Working with a partner, discuss what you think has happened in this reaction. Use the information in the diagram to write a balanced chemical equation to describe what has happened. What type of reaction is this?

questions 1.� 8. Scientists find the activity series shown in Figure

1.29 to be a useful tool in predicting whether two substances will react. A reaction will occur as a more reactive element replaces a less reactive one lower in the series.

In Science@work1.4, copper replaced the silver in silver nitrate solution to form copper nitrate. Use the activity series to predict whether a reaction will occur for each of the following. Write a balanced reaction for each of the reactions that you think will occur. Present your answers in a table.

(a) Aluminium is added to copper nitrate solution.

(b) Magnesium is added to hydrochloric acid (hydrogen chloride).

(c) Silver is added to magnesium nitrate solution.

(d) Zinc is added to lead chloride solution.

beaker

blue copper sulfate solutionbrown deposits

of copper formon iron nail Figure 1 .�8

What is happening in this reaction?

Figure 1 .�9 Activity series of metals.

9. List the types of industries you think would make use of such tables as that shown in Figure 1.29. Include examples.

10. Conduct some research into the preparation of one of the ionic compounds you have used in this chapter, such as copper sulfate, calcium carbonate, silver nitrate or hydrochloric acid. Using a format of your choice, write a report about how laboratories prepare samples of this product.

sodium mostreactive

magnesium

aluminium

zinc

iron

nickel

tin

lead

hydrogen

copper

silver

platinum

gold leastreactive

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�� Heinemann Science Links 4

Energy changes during reactionsWe have now looked at various types of reactions that may occur, and have practised how to balance a chemical equation. We have not, however, considered the energy changes that take place in a chemical reaction.

Whenever energy is given out during a chemical reaction, the reaction is said to be exothermic. When plant and tree matter react with oxygen in the air in a bushfire, enormous amounts of heat and light are emitted in the process. Another exothermic reaction is occurring right now within your body. As your cells ‘burn up’ food in the reaction with oxygen that is called respiration, heat is produced.

Because exothermic reactions give off energy, the energy of the products formed is actually less than that of the reactants. For example, as wood burns, stored energy is released and heat is given off. You can look at Figure 1.31 to study how these energy levels vary before and after burning wood.

In contrast, sometimes energy is absorbed from the surroundings in a chemical reaction. In this case, the reaction is said to be endothermic. To see an example of such a reaction, just stand next to your favourite green plant in the daytime. The chlorophyll in the leaves of the plant captures light energy during the process of photosynthesis. This energy is used to manufacture glucose and oxygen from carbon dioxide and water. Because energy must be added for an endothermic reaction to occur in this case, the energy of the products formed is greater than that of the reactants. Have a look at Figure 1.32 to see how this works in the case of photosynthesis.

A question of energy1.4

Figure 1 .�0 Here’s a creature that can shed a little light on this topic! An exothermic reaction occurs in a firefly, and energy is released in the form of visible light.

Storedenergyof wood

Heat is given offduring reaction

Burning Wood

Stored energy ofcharcoal and ashes

Time

Ener

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Figure 1 .�1 Energy, in the form of heat and light, is released when the reaction occurs. This is called an exothermic reaction.

Figure 1 .�� Some cold packs use endothermic reactions. The reactions absorb energy and the pack becomes cold.

Carbon dioxide+ water

Glucose + oxygen

Photosynthesis

Energy is addedin the form ofsunlight

Time

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Figure 1 .�� Energy, or heat, must be added for the reaction to occur. Because energy is added, this is called an endothermic reaction.

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S C I E N C E work

Energy changes of reactions

Aim

To observe the energy changes that take place during some chemical reactions.

Materials

• sodium thiosulfate powder (Na2S2O3) • potassium nitrate powder (KNO3)• ammonium nitrate powder (NH4NO3) • ammonium chloride powder (NH4Cl)• sodium nitrate powder (NaNO3) • sodium chloride powder (NaCl)• Styrofoam cups • thermometer (–10 to 110°C)• measuring cylinder • spatula• distilled water • stirring rod

Safety

Potassium nitrate and ammonium nitrate are both irritants to the eyes and skin. Use with care, and if contact with eyes or skin occurs, rinse very thoroughly with water. Complete an RAS before you start this activity.

Method

1. Place 50 mL of water into a Styrofoam cup and measure its temperature.�. Add a spatula of sodium thiosulfate, stir briefly and record the final temperature of the reaction

mixture.�. Repeat steps 1 and 2 for each of the other substances.4. Record your results in a table that includes the name of each substance, the initial temperature

and final temperature.

Discussion

1. How can the results of this experiment be used to determine which reactions are exothermic and which are endothermic?

�. Make a list of exothermic reactions, a list of endothermic reactions and a list of reactions that you are unsure of.

�. Plot a column graph to show each of the substances and their final temperatures. Include a line across the graph that shows the initial temperature of the water.

4. Why do you think Styrofoam cups were used instead of beakers?

Conclusion

Make a summary of the energy changes you have observed in this experiment.

Evaluation

Do you think your experiment was a success? List any difficulties or sources of error that you encountered. Beside each, suggest an improvement.

Extension

Select one of these reactions or another that interests you and measure the temperature as it changes over time (maybe at 10 second intervals). Plot a line graph showing how the temperature changes. If a temperature probe is used, your computer can generate this graph.

EXPERIMENT 1 . 1 1!

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�8 Heinemann Science Links 4

If you were to purchase a new car today, it would come with a driver’s airbag and possibly passenger and side airbags. Airbags have been around since the 1980s.

Originally patented in 1953, it has taken some time to refine the design, in which timing is of critical importance. In order to protect people during a collision, an airbag must inflate within 40 milliseconds and start to deflate when contact is made. Inflate too late and the damage has been done; and if too early, a person is at risk of being injured by the airbag itself, which would feel like colliding with a rock if hit while inflating.

Inside an airbag is a gas generator. This consists of a mixture of sodium azide (NaN3), potassium nitrate (KNO3) and silicon dioxide (SiO2). These solids take up only a small volume while contained in a canister in the airbag.

When crash sensors in the car detect a life-threatening impact, an electronic impulse ignites the sodium azide. This creates the temperatures over 300°C that are required for sodium azide to decompose, which it does according to the equation:

2NaN3(s) → 2Na(l) + 3N2(g)

The nitrogen gas produced inflates the airbag. It is important to remove the sodium metal that is produced in this reaction as it is potentially an explosive substance. This explains the presence of the potassium nitrate because the molten sodium metal will react with this as follows:

10Na(l) + 2KNO3(s) → K2O(s) + 5Na2O(s) + N2(g)

The nitrogen gas produced from the two reactions inflates the airbag. The other products combine with silica (SiO2) to form a harmless, glassy solid.

Heinemann Science Links 4�8

scie

nce airbags

Figure 1 .�4 An airbag inflates within 40 milliseconds to protect people involved in a collision. It acts to reduce injury through contact with the steering wheel and dashboard features. When deployed correctly, the airbag will also act to increase the time over which the contact occurs, lessening the impact on the person in the car. Contact with the airbag will also spread this force over a larger area of the body, which reduces the likelihood of severe injury.

in action

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�9�9

airbagsquestions 1. Describe what happens to pellets of sodium azide when they are ignited.

�. An airbag works because it can be filled within a very short time with nitrogen gas. Name two ways in which this gas may be produced in the reactions within the airbag.

�. The canister containing sodium azide and potassium nitrate also contains silica. What is the silica for?

�. Sodium azide (NaN3) is a strong and potentially carcinogenic poison. The majority of cars when no longer needed are eventually flattened in a recycling plant. Conduct some research to discover how these poisons that reside within airbags that have never been deployed are removed safely.

4. Should all cars be required to be fitted with side airbags? Do some research and then conduct a class debate on this topic.

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�0 Heinemann Science Links 4

The need for speedIncreasing the speed of reactionsThe reactions selected for you to perform in the laboratory are meant to allow you to see an almost instant result. In Science @ work 1.3 the production of hydrogen gas would have started almost as soon as you added the acid to the zinc. In Science @ work 1.4, however, the reaction is best observed over a lesson or even overnight.

You may recall from Heinemann Science Links 2 that we can increase the speed of a chemical reaction by increasing:ü the concentration of one or more of the reactantsü the temperature at which the reaction occursü the surface area of one or more of the reactants.

If you had used an acid of higher concentration in Science @ work 1.3, the reaction would have proceeded faster since the reactant particles could collide more frequently and react more often. A similar effect would have been possible by using powdered zinc instead of solid lumps since the surface area of the zinc would be greater. Sitting the reaction mixture in an ice bath would slow the reaction down since the reacting particles wouldn’t have as much energy to move around, collide and react.

Some reactions will proceed more quickly with the addition of a chemical called a catalyst. In industrial chemistry, where products are being manufactured, there are obvious cost benefits in being able to speed up a reaction. A catalyst helps the reaction to proceed, usually by providing a surface on which the reaction can occur. It is therefore not used up in the reaction. For example, iron is used as a catalyst in the chemical reaction called the Haber process in which nitrogen and hydrogen combine to form ammonia. This product has uses in many industries, including the manufacture of fertiliser. Exhaust systems in modern vehicles contain catalysts that help reduce the toxicity of the exhaust gases.

Some reactions that you may have witnessed, like fireworks exploding or even cars bursting into flames in a movie, happen very fast. Other reactions are not quite as breathtaking. Watching a chipped panel of a car slowly rust is never going to replace other forms of entertainment!

scifile

Figure 1 .�5 This is a computer model of the structure of a substance called a zeolite. A zeolite is found within volcanic rock and can be used as a catalyst. These catalysts are used to speed up reactions that break long-chain hydrocarbons from crude oil into compounds with shorter structures, such as those in petrol.

Figure 1 .�� This photo shows what happens when a strip of magnesium metal is placed into a test-tube of 6 M hydrochloric acid, and then into extremely concentrated 15 M hydrochloric acid. The test-tube on the left shows magnesium in 15 M hydrochloric acid. The test-tube on the right shows a strip of magnesium in 6 M hyrochloric acid. In which test-tube does the magnesium react most violently? Why do you think acids of high concentration must be handled with great care in the laboratory?

catalytic converter

Figure 1 .�7 Exhaust gases from a car engine are channelled through a network of holes in the converter. As the more poisonous gases, such as carbon monoxide, make contact with the platinum and rhodium metals used in the converter, they combine with oxygen to produce the less toxic carbon dioxide gas, which is released from the car.

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S C I E N C E work

Using a catalystManganese dioxide acts as a catalyst in the decomposition of hydrogen peroxide, which produces oxygen gas and water.

Aim

To produce and test for oxygen gas and illustrate the action of a catalyst.

Materials

• manganese dioxide powder (MnO2) • 5% hydrogen peroxide solution (H2O2)• test-tube • aluminium foil (Al)• spatula • glowing splint

Safety

Take care when using H2O2 because it can cause serious burns to skin and damage to eyes. In case of contact with skin, wash with lots of water. Remove contaminated clothing before it dries out and rinse thoroughly. Complete an RAS before you start this activity.

Method

1. Place about a quarter of a spatula of manganese dioxide into the test-tube.

�. Measure out 5 mL of hydrogen peroxide solution. Pour it into the test-tube and quickly cover the opening of the test-tube with the aluminium foil.

�. When a reasonable amount of gas has collected (and while the reaction is still bubbling), remove the aluminium foil and plunge the glowing splint into the gas in the test-tube.

4. Record your observations.

Discussion

1. What changes did you observe that indicated a chemical reaction had taken place?�. Describe the appearance of the gas produced.�. After the reaction, the liquid remaining is water. The word equation for this reaction is: manganese dioxide hydrogen peroxide oxygen + water

Notice that the name of the catalyst goes above the arrow. Write the equation using chemical formulae.

4. Why do you think the manganese dioxide label was added above the arrow in the equation, rather than being listed on the left-hand side as a reactant?

Conclusion

Create a SWOT analysis chart for this activity.

Evaluation

Are you satisfied that no manganese dioxide was used up in this reaction, and that it purely acted as a catalyst for the decomposition of hydrogen peroxide? Can you think of a way to test if this is the case?

Extension

Design a method for determining the amount of manganese dioxide present before and after the reaction has taken place. Predict whether the amount of manganese dioxide will be the same. After checking your method with your teacher, test your prediction. Include an RAS in your method.

EXPERIMENT 1 . 12!

Figure 1 .�8 A glowing splint is used to test for oxygen gas.

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�� Heinemann Science Links 4

questions 1 .4 1. Silver is a catalyst in a reaction to make

formaldehyde, which is the basis of some adhesives and plastics. Silver is expensive, but its cost adds very little to the overall cost of making these products. Discuss this with a partner and see if you can explain why.

�. The Greek prefix exo– means ‘outside’. How does the word outside relate to exothermic reactions? What other words do you know that start with this prefix?

�. Methane gas will react with oxygen to produce carbon dioxide and water, as shown by the equation:

CH4 + 2O2 → CO2 + 2H2O The energy of the products formed by this

reaction is less than the initial energy of the reactants. Do you think this reaction is endothermic or exothermic? Explain why.

4. Hydrogen and oxygen can combine chemically to form water and energy:

hydrogen + oxygen → water This reaction and the energy evolved can be

represented as shown in Figure 1.39. (a) List which substances are the reactants

and which are the products.

Given that this reaction is endothermic, draw an energy diagram similar to Figure 1.39 to describe this reaction.

5. Athletes who play contact sports may use cold packs to ice down bruises. Those who undertake alpine sports are more likely to need hot packs to generate warmth. Below are the contents and reactions in two sports packs.

Pack 1 contains powdered Fe, activated carbon, NaCl, sawdust and water in an air-permeable bag. Upon breaking the inner sachets, the exothermic reaction occurring is:

4Fe(s) + 3O2(g) → 2Fe2O3(s) Pack 2 contains sachets of NH4NO3 and water,

and its endothermic reaction is: NH4NO3(s) → NH4

+(aq) + NO3–(aq)

Which of the packs is suitable for a footballer? Which is suitable for a Nordic skier? Present your choices, including reasons, as a T-chart for the two types of athletes.

�. Copy and complete the following statement. We can increase the rate of a chemical reaction

by increasing the ____________ of one or more of the reactants, increasing the ____________ at which the reaction occurs, increasing the ___________ area of one or more of the reactants or by the addition of a ____________.

7 . Discuss with a partner the statement: ‘A catalyst speeds up a reaction but takes no part in the reaction.’ Can you come up with a better way of explaining how catalysts work? Compare your explanation with that of others in your class.

8. Enzymes in our bodies act as biological catalysts. What types of chemical reactions do you think they assist? Conduct some research to explore this area further and prepare a report of your findings, using a format of your choice.

9. In this chapter, it was mentioned that a major industrial reaction is the synthesis of ammonia. This is usually done using a method called the Haber process. Research the ways in which catalysts are important in this process. Present your findings using a format of your choice.

Hydrogen andoxygen

Water

Time

Ener

gy

Figure 1 .�9

(b) Looking at the difference in energy before and after the reaction has occurred, state whether this reaction is exothermic or endothermic.

(c) Iodine and chlorine gas react to form the compound iodine chloride, according to the equation:

I2 + Cl2 → 2ICl

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Brigid Brignell: Editor (Secondary Science), Harcourt Education Australia and UK

I’ve always loved science and in Year 11 and 12 I did mostly maths and science subjects. At the end of Year 12 I wanted to continue studying chemistry and also stick with my English and humanities subjects. Eventually I decided that I could combine the two things.

I completed a Bachelor of Arts and a Bachelor of Science at The University of Melbourne and then used the combination of the two to move into an editing job within a publishing company. I specialised in science material — books, revision guides, CDs and teacher resources — but I have also edited some other subjects.

In Australia, I have worked on the Heinemann Queensland Science Project and the Science Links series. Not only have I been a part of editing the books and CDs, but I have also given input into the design and layout of the books, helped select the photos, liaised with the authors and of course looked at the science content of each book. It’s also fun to check the animations and other interactive material, working with designers and developers to make sure that the author’s vision resembles the final product that students see.

My job has also given me the opportunity to transfer over to the UK office for a year. This has been a great experience to work within the company but in a different country. Within the science department in the UK I have worked on student and teacher resources for their GCSE-level science classes (about Year 9 and 10 in Australia). I’ve gained a different perspective on the publishing industry and science books and other resources for secondary schools, and I’ve also been able to squeeze in some travel!

My background in science not only enables me to edit the books, but also to have a good idea of what science students will find interesting. A good dynamic photo or a really clear illustration can often be much more interesting than reading a huge block of text.

It’s really exciting and rewarding to see the final product, printed and bound. I’ve even been lucky enough to have some of my books nominated for awards. It’s great to know that there are science students in schools across the country who are using the books every day. I hope that some of them find the books interesting (or even inspiring) and are encouraged to pursue a career in science.

Figure 1.40Brigid Brignell.

Society of Editors (Victoria)Victorian Writers CentreJob Guide for Victoria (published annually by the Commonwealth Department of Education and Training)VTAC Guide (published annually by the Victorian Tertiary Admissions Centre)

Science writer, journalist, copywriter

Figure 1.41As well as editing part of the Science Links series, Brigid was involved in the design, layout and graphic presentation of the texts.

e interactive CDincluded

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4VELS EditionHelen CochraneJacinta DevlinGary SimpsonRhonda Coffey

Carmel FryElizabeth Pizarro-Campagna

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Jacinta Devlin

Helen Cochrane

Gary Simpson

Rhonda Coffey

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Jacinta DevlinHelen CochraneRhonda Coffey

Hein

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Chapter reviewK

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review questions

anioncatalystcationchemical equationchemical reactioncovalent bonddecompositiondouble replacementendothermicexothermic

ionic compoundlaw of conservation of massmolecular compoundprecipitateproductsreactantssingle replacementsynthesisvalence shell

1. Use Table 1.1 to assist you with writing the chemical formulae of the following ionic compounds.

(a) hydrogen nitride (b) sodium bromide (c) barium sulfate (d) zinc chloride (e) aluminium bromide (f) potassium carbonate (g) ammonium phosphate �. (a) Create a mind map to explain the difference

between an electron dot diagram and a structural formula to show the arrangement of atoms in a molecular compound. You may wish to refer back to Table 1.3 for assistance. Include a few examples in your map.

(b) Draw the electron dot diagram and the structural formula for the molecular compound carbon tetrachloride (CCl4).

�. Consider the combustion of methane CH4: CH4 + O2 → CO2 + H2O methane + oxygen → carbon dioxide + water (a) Name the reactants and the products in this

chemical reaction. (b) Balance the equation. 4. Test your juggling skills by balancing the following

equations. (a) C3H8(g) + O2(g) → CO2(g) + H2O(l) (b) FeSO4(aq) + NaOH(aq) →

Fe(OH)2(s) + Na2SO4(aq) (c) Na2CO3(aq) + Ca(OH)2(aq) →

CaCO3(s) + NaOH(aq) (d) Fe(s) + H2O(l) → Fe3O4(s) + H2(g) (e) CaH2(s) + H2O(l) → Ca(OH)2(aq) + H2(g) (f) SO2(g) + O2(g) → SO3(g) (g) NO(g) + O2(g) → NO2(g) (h) N2(g) + H2(g) → NH3(g) (i) ZnO(s) + HCl(aq) → ZnCl2(aq) + H2O(l)

5. Write balanced equations for the following reactions. (a) Hydrochloric acid reacts with aluminium,

forming hydrogen gas and aluminium chloride. (b) Hydrochloric acid and aluminium hydroxide

react to give water and aluminium chloride. (c) Magnesium nitrate and water form from the

reaction between nitric acid and magnesium hydroxide.

(d) Zinc carbonate reacts with nitric acid to give water, carbon dioxide gas and zinc nitrate.

�. In Science@work1.3 you observed the reaction: Zn + 2HCl → H2 + ZnCl2 Make up a set of cards with the formulae for each

of the reactants and products. Using these cards, explain to a classmate how the reactants and products are balanced using the ratios of reactants that are listed in this equation. If possible, use multimedia to produce an animated version of your explanation.

7 . Write balanced equations for these reactions. (a) Benzene (C6H6) burns in the presence of

oxygen to give carbon dioxide and water. (b) Rust is iron oxide (Fe2O3) formed as iron reacts

with oxygen in the air. 8. Write a diary entry or the scene of a B-grade horror

movie in which you describe the fictitious day that the science laboratory at school caught fire. Use some scientific terms, like chemical reactants, products, exothermic, energy, release, heat, temperature, or concentration. You can create a few colourful student and teacher characters to help tell your story. Afterwards, share your stories with your classmates—just don’t test them out! Ask for feedback and refine your presentation where needed.

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�5

9. Figure 1.42 shows the change in energy for four different reactions: I, J, K and L.

10. Refer back to Figure 1.29 about the activity series to answer the following question.

Jeff conducts a test by placing three different unknown metals (X, Y and Z) in solutions of magnesium chloride, lead chloride and silver chloride. His results appear in Table 1.6. List the unknown metals in order of activity from most to least reactive using the information in Table 1.6. Write a justification for your list.

Table 1.� Jeff’s results

X Y Z

Magnesium chloride

No reaction No reaction No reaction

Lead chloride

No reaction Metal crystals form

No reaction

Silver chloride

Metal crystals form

Metal crystals form

No reaction

Figure 1 .4�

products

reactants

Time

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(a) Which reactions are exothermic? (b) Which reactions are endothermic? (c) Which reaction absorbed the most energy? (d) Which reaction released the most energy?

In the Thinkingabout at the start of this chapter, you imagined that you were battling the elements of nature and humanity on the set of ‘Survivor—Chemical Island’. How did you respond to the challenge?

You were given a task of classifying some substances around you as ionic, molecular or metallic compounds. Look back at the way you grouped these compounds. Hopefully, if you found this task difficult, you could now rise to the occasion. Calcium carbonate (CaCO3), aluminium oxide (Al2O3), sodium chloride (NaCl) and iron oxide (Fe2O3) are of course all ionic substances. Water (H2O), oxygen gas (O2), silicon dioxide (SiO2) and carbon dioxide gas (CO2) are all molecular compounds and, lastly, you must have picked the gold nugget as metallic. Would you still be in the running to win the cash?

To kill some further time, you were also asked to list or describe any chemical reactions that these substances may have been involved in. With the benefit of your experience in working through this chapter, see how many such reactions you can add to your previous list. Are there aspects about chemistry that you would like to learn more about? Include these in your KWLH.

reflection chemical reactionscomplete

products

reactants

Time

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products

reactants

Time

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products

reactants

Time

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I J

K L

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