Chapter 12 Chemical Changes

Question 0

What are the characteristics of a chemical change?

Answer 0

A new substance is formed.
 • A solid appears or disappears. 
• The temperature of the substances changes spontaneously. 
• A colour change occurs.
 • Bubbles appear. 
• A flame appears or light is produced.

Question 1

What is a characteristic of a physical change?

Answer 1

Another characteristic of a physical change is that it is usually reversible. Water can be turned into ice and then back into water again very easily.

It does not break the bonds between the atoms

Question 2

What are some examples of chemical changes?

Answer 2

• hard boiling an egg

- apple turning brown

Question 3

What is a chemical reaction?

Answer 3

The process of producing new substances is a chemical reaction.

Question 4

What are reactants?

Answer 4

The substances that react together are the reactants.

Question 5

What are the products?

Answer 5

The new substances that are formed.

Question 6

What happens to the bonds?

Answer 6

The bonds between the atoms of the reactants break and new bonds are made between the atoms to form the products.

Question 7

What are the types of chemical reactions?

Answer 7

• Decomposition
• Synthesis
• Combustion
• Oxidation (Displacement)

Question 8

What happens in decomposition reactions?

Answer 8

In decomposition reactions, a reactant breaks up (or decomposes) to form two or more products. The decomposition is often the result of heating or passing electrical current through the reactant.

Question 9

What happens in synthesis reactions?

Answer 9

Occurs when two or more reactants combine to form a single substance.

Question 10

What happens in a combustion reaction?

Answer 10

Combustion reactions always have oxygen as a reactant.

Question 11

What happens in a displacement reaction?

Answer 11

In a displacement reaction, metals combined with non-metals in the reactants swap partners to form new combinations.

Question 12

What is reaction rate?

Answer 12

The speed with which a chemical reaction occurs is called its reaction rate.

Question 13

Example of a fast reaction rate?

Answer 13

The explosive reaction between hydrogen and oxygen to form water is very fast and can release enough energy to propel spacecraft into orbit.

Question 14

Example of slow reaction rate.

Answer 14

Other reactions, such as the rusting of iron, can take weeks, months or even years to be complete.

Question 15

Why should we change the temperature?

Answer 15

When particles collide, the bonds between atoms may break and new bonds may form. As the added heat increases the number of collisions, the breaking and creation of bonds occurs faster.
In other words, the chemical reaction between substances occurs much faster if you heat them.
Of course, this works the other way as well; cooling the substances involved in a chemical reaction reduces the reaction rate.

Question 16

Why do we store food in the refrigerator?

Answer 16

Food goes off when micro-organisms produce chemical substances that degrade the food. Food is much cooler in the fridge than on the bench, and this reduces the rate at which the micro-organisms produce degrading substances.

Question 17

What are catalysts?

Answer 17

Catalysts are chemicals that speed up chemical reactions.

Question 18

Why should we change the surface area?

Answer 18

When you break up a substance into smaller pieces, you increase the surface area of that substance. This means that more particles can immediately come into contact with the particles of another substance, allowing reactions between them to happen much faster.

Question 19

How do bath bombs work?

Answer 19

Bath bombs, for example, are sold as solid balls that are dropped into your bath water to release carbon dioxide gas and scented oil. As the water reacts with the Epsom salts in the bath bomb, it slowly disappears. However, if you crush the bath bomb into a powder and then put it in your bath, it reacts very quickly.

Question 20

Why are catalysts not reactions?

Answer 20

They are not reactants because they are not changed by the reaction.

Question 21

Example of a catalysts.

Answer 21

For example, catalytic converters in car exhausts use a precious metal, such as platinum, as a catalyst. This enables nitrogen oxide to react with toxic gases, such as carbon monoxide, to form the less harmful carbon dioxide and nitrogen gases; this reaction would not occur in the absence of platinum.

Question 22

What are enzymes?

Answer 22

Catalysts produced by living organisms are called enzymes. Many of the chemical reactions taking place inside your body involve enzymes.Enzymes are also responsible for some of the changes we see in our food

Question 23

What are phenolics?

Answer 23

Apples and other fruits go brown because chemicals in them, called phenolics, react with oxygen in the air.

Question 24

What are quinones?

Answer 24

The brown chemicals produced are called quinones.

Question 25

What does amylase do?

Answer 25

Amylase helps us digest starches.

Question 26

What does protease do?

Answer 26

Protease is needed for protein digestion.

Question 27

What does lipase do?

Answer 27

Lipase must be present if we are to digest fats and oils.

Question 28

What are type of enzymes?

Answer 28

Phenolics, 
quinones, 
amylase, 
Protease, 
lipase

Question 29

What does the concentration depend on?

Answer 29

The concentration of a solution depends on how much solute is dissolved in a set amount of solvent.

Question 30

What happens when more solute is dissolved?

Answer 30

The more solute that is dissolved, the greater the concentration of the solution is. The more concentrated that a solution is, the more particles of solute it contains that can react with other substances.

Question 31

What happens when there are more particles?

Answer 31

The more particles of solute it contains that can react with other substances.

Question 32

When to use a dilute solution?

Answer 32

Use more dilute solutions to make a reaction go more slowly.

Question 33

When to use a concentrated solution?

Answer 33

Use more concentrated solutions to make a reaction go faster.

Question 34

What is corrosion?

Answer 34

Corrosion is a chemical reaction between a metal and substances in its environment that results in the metal being ‘eaten away’

Question 35

What is the most common form of corrosion?

Answer 35

The most common form of corrosion that we encounter is the corrosion of iron, a process referred to as rusting.

Question 36

Chemical equation of rust.

Answer 36

When iron reacts with water and oxygen in the air it forms iron oxide and other iron compounds that make up the familiar red-brown substance known as rust. Rusting is a chemical reaction that can be represented by the following word equation:

iron + water + oxygen rust

Question 37

What is weakened by rusting?

Answer 37

Even strong buildings and bridges that are made from steel, an alloy of iron, are weakened by rusting. The Sydney Harbour Bridge, for example, is continually being painted to protect it from moisture and the air, which would cause its steel girders to rust. Ships and cars are also constructed largely of steel.

Question 38

What can make rusting happen faster?

Answer 38

One of the most effective of these is salt. Some chemicals released from factories may not be corrosive themselves but may allow the rusting process to occur faster.

Question 39

Example of salt making reaction time faster.

Answer 39

Steel dinghies that are used in the ocean rust much faster than those that are used only in fresh water.

Question 40

Where are corrosion rates faster?

Answer 40

Even the exhaust from aircraft can speed up rusting. Research by the CSIRO has found that corrosion rates in a large city are highest near airports, industrial plants, sewage treatment works and large bodies of salt water.

Question 41

Where rusting occurs slower and an example.

Answer 41

Rusting is much slower in very dry environments such as deserts. In the Mohave Desert in southern California, hundreds of aircraft that are not in immediate use by airlines are stored in the open air. Due to the extremely low humidity — the rainfall is nearly zero — rusting occurs extremely slowly.

Question 42

What causes more rusting to occur?

Answer 42

The layer of rust that forms on an iron object flakes off the metal, allowing air and moisture to get through to the iron below.

Question 43

What are the ways of protecting iron and steel?

Answer 43

One way is to prevent oxygen or moisture from contacting the metal.

Question 44

What is surface protection?

Answer 44

One way is to prevent oxygen or moisture from contacting the metal. This is called surface protection.

Question 45

The metal can be protected by coating with…..

Answer 45

The metal can be protected by coating it with paint, plastic or oil.

Question 46

Why use surface protection?

Answer 46

If the surface protection becomes scratched or worn off, the metal below can be attacked by moisture and oxygen and rusting will occur.

Question 47

How is rusting useful?

Answer 47

You can buy, from a pharmacy, hand warmers, which are commonly used by skiers and campers. These packages produce heat when you shake them. The contents of the packet include powdered iron, water, salt and sawdust. When the packet is shaken vigorously, the iron undergoes a rusting reaction, which produces heat.

Question 48

What are the reactions that involve oxygen as a reactant?

Answer 48

Reactions that involve oxygen as a reactant are called combustion or oxidation reactions.

Question 49

What are fossil fuels?

Answer 49

Fossil fuels are those fuels that are formed from the remains of living things.

Question 50

Examples of fossil fuels.

Answer 50

Petrol, natural gas and coal are fossil fuels.