Chemisty

Question 1

What are atoms joined together by?

Answer 1

Atoms are joined together by chemical bonds, which involve the electrons found around the nucleus of the atom. Covalent bonds and ionic bonds are two types of chemical bonds.

Question 2

All substances are made from what?

Answer 2

All substances are made from atoms.

Question 3

What does an atom have?

Answer 3

An atom has a small central nucleus surrounded by even smaller particles called electrons. The nucleus is positively charged, and the electrons are negatively charged

Question 4

Are all atoms the same?

Answer 4

No. All atoms are different. Any given element is made of atoms of just one particular sort. The atoms of any element are different to the atoms of any other element. So iron is made from a different sort of atom to sulfur, and carbon atoms are different to oxygen atoms.

Question 5

Atoms of each element are represented by chemical symbols. What is the format of chemical symbols?

Answer 5

Chemical symbols usually consist of one or two different letters, but three letters are sometimes used for newly discovered elements.

The first letter in a chemical symbol is always an UPPER CASE letter. The other letters are always lower case. So, the symbol for magnesium is Mg, and not mg, MG or mG.

Every element has its own chemical symbol. For example, iron is Fe, sulfur is S, sodium is Na and oxygen is O.

Question 6

What does the small 2 after an element tell you?

Answer 6

The small 2 after an element tells you there are two atoms of that particular element in each molecule. For example, the water molecule H2O has two hydrogen atoms. Notice that you do not write a number 1 if there is only one atom of an element in a molecule.

Question 7

What do chemical equations show?

Answer 7

Chemical equations show what happens in a reaction. In general, we write:
reactants → products

The reactants are the substances that react together. The products are the substances produced in the reaction. Individual substances are separated by a plus sign.

Question 8

What does a word equation give?

Answer 8

A word equation gives the names of the substances involved in a reaction. For example:
copper + oxygen → copper(II) oxide

Copper and oxygen are the reactants, and copper(II) oxide is the product.

Question 9

What do Balanced equations give?

Answer 9

Balanced equations give the symbols and formulas of the substances involved in a reaction. In the example above, if we just replace the words shown above with the correct chemical formulas, we will get an unbalanced equation, as shown here:
Cu + O2 → CuO

Question 10

How do you make a balanced equation?

Answer 10

To make a balanced equation, we need to adjust the number of units of some of the substances until we get equal numbers of each type of atom on both sides of the arrow.
Here is the balanced symbol equation:
2Cu + O2 → 2CuO

Question 11

Examples of balanced equations

Answer 11

• Mg + Cl2 → MgCl2
• 2Na + Cl2 → 2NaCl
• 4Fe + 3O2 → 2Fe2O3
• 4Na + O2 → 2Na2O
• 2Na + 2H2O → 2NaOH + H2.

Question 12

Steps to writing the balanced equation for the reaction between hydrogen and oxygen to produce water.

Answer 12

•	Step 1
Write the formulae for each substance:
H2 + O2 → H2O
•	Step 2
Check for an unbalanced element, for example, O. Adjust the number of each atom or molecule needed, but never change a formula. We need two O atoms on each side:
H2 + O2 → 2H2O
•	Step 3
Check for another unbalanced element. In this example, there are 2 H atoms on the left and 2 × 2 = 4 atoms on the right. So, we need to double the number of hydrogen molecules:
2H2 + O2 → 2H2O

Question 13

Steps to writing the balanced equation for the reaction between calcium and water to produce calcium hydroxide and hydrogen.

Answer 13

•	Step 1
Write the formulae for each substance:
Ca + H2O → Ca(OH)2 + H2
•	Step 2
Check for one unbalanced element, for example, O. Adjust the number of each atom or molecule needed, but never change a formula. We need two Os on each side:
Ca + 2H2O → Ca(OH)2 + H2
•	Step 3
Check for another unbalanced element. In this example, the equation is now balanced.

Question 14

Why is copper used for wiring

Answer 14

It is a good conductor of electricity.

Question 15

What are metal particles held together by?

Answer 15

Metal particles are held together by strong metallic bonds, which is why they have high melting and boiling points. The free electrons in metals can move through the metal, allowing metals to conduct electricity. Superconductors have little or no electrical resistance.

Question 16

What are the 6 typical physical properties that metals have?

Answer 16

1. Lustrous (shiny)
2. Hard
3. High density (are heavy for their size)
4. High tensile strength (resist being stretched)
5. High melting and boiling points
6. Good conductors of heat and electricity

Question 17

Why is iron used to make cars and bridges?

Answer 17

It is hard, with a high tensile strength

Question 18

What is an unreactive metal?

Answer 18

Metals that do not easily take part in chemical reactions. For example, platinum does not react with oxygen in the air, even if it is heated in a Bunsen burner flame.

Some metals are very reactive. They easily take part in chemical reactions to make new substances.

Magnesium is very reactive. It ignites when heated and burns with a brilliant white flame.

Other metals may be more reactive than magnesium, or in between magnesium and platinum. If we put the metals in order of their reactivity, from the most reactive down to the least reactive, we get a list called the reactivity series.

Question 19

What are reactive metals?

Answer 19

Some metals are very reactive. They easily take part in chemical reactions to make new substances.

Magnesium is very reactive. It ignites when heated and burns with a brilliant white flame.

Other metals may be more reactive than magnesium, or in between magnesium and platinum. If we put the metals in order of their reactivity, from the most reactive down to the least reactive, we get a list called the reactivity series.

Question 20

What do displacement reactions involve?

Answer 20

Displacement reactions involve a metal and a compound of a different metal. In a displacement reaction, a more reactive metal will displace a less reactive metal from its compounds. Displacement reactions are easily seen when a salt of the less reactive metal is in the solution.

Question 21

What happens during a displacement reaction?

Answer 21

During the reaction, the more reactive metal gradually disappears as it forms a solution. The less reactive metal coats the surface of the more reactive metal.

Question 22

What is the order of reactivity starting with most reactive first?

Answer 22

• magnesium
• zinc
• iron
• copper

Magnesium displaces three metals, zinc displaces two metals, iron displaces one metal and copper does not displace any of the other three metals.

Question 23

What is an alloy?

Answer 23

An alloy is a mixture of two elements, one of which is a metal. Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone. For example, alloys are often harder than the metal they contain.

Question 24

Why are alloys harder than pure metal?

Answer 24

Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal.

Question 25

How can the rate of a reaction be measured?

Answer 25

The rate of a reaction can be measured by the rate at which a reactant is used up, or the rate at which a product is formed.

Question 26

What are all factors that affect the rate of a reaction.

Answer 26

Temperature, concentration, the pressure of reacting gases, the surface area of reacting solids, and the use of catalysts.

Question 27

What causes a greater rate of reaction?

Answer 27

The more frequently particles collide and the greater proportion of collisions with enough energy.

Question 28

What’s the difference between low and high rates of reaction?

Answer 28

Reactions that happen slowly have a low rate of reaction (rocks). Reactions that happen quickly have a high rate of reaction (explosion).

Question 29

What are the two ways to measure the rate of reaction?

Answer 29

1. Measure the rate at which a reactant is used up
2. Measure the rate at which a product is formed

The method chosen depends on the reaction being studied.

Question 30

How do you measure mass of substance?

Answer 30

The measurement itself depends on the nature of the reactant or product:
• The mass of a substance - solid, liquid, or gas - is measured with a balance

Question 31

How do you measure the volume of a gas?

Answer 31

The measurement itself depends on the nature of the reactant or product:
• The volume of a gas is usually measured with a gas syringe, or sometimes an upside-down measuring cylinder or burette

Question 32

What are five ways the rate of reaction increases?

Answer 32

• The temperature is increased
• The concentration of a dissolved reactant is increased
• The pressure of a reacting gas is increased
• Solid reactants are broken into smaller pieces
• A catalyst is used

Question 33

What is activation energy?

Answer 33

For a chemical reaction to occur, the reactant particles must collide. Collisions with too little energy do not produce a reaction.

The collision must have enough energy for the particles to react. The minimum energy needed for particles to react is called the activation energy.

Question 34

What happens if the concentration of a dissolved reactant is increased, or the pressure of a reacting gas is increased?

Answer 34

• There are more reactant particles in the same volume
• There is a greater chance of the particles colliding
• The rate of reaction increases

Question 35

What happens if a solid reactant is broken into small pieces or ground into a powder?

Answer 35

• Its surface area is increased
• More particles are exposed to the other reactant
• There is a greater chance of the particles colliding
• The rate of reaction increases

Question 36

What if the temperature is increased?

Answer 36

• The reactant particles move more quickly
• More particles have the activation energy or greater
• The particles collide more often, and more of the collisions result in a reaction
• The rate of reaction increases

Question 37

Why are catalysts important in industry?

Answer 37

Catalysts are important in industry because they reduce costs.

Question 38

How do catalysts work?

Answer 38

Catalysts increase the rate of reaction without being used up. They do this by lowering the activation energy needed. With a catalyst, more collisions result in a reaction, so the rate of reaction increases. Different reactions need different catalysts.

Question 39

What is a catalyst?

Answer 39

A catalyst is a substance that can increase the rate of a reaction. The catalyst itself remains unchanged at the end of the reaction it catalyzes. Only a very small amount of catalyst is needed to increase the rate of reaction between large amounts of reactants.

Question 40

Why do modern cars have a catalytic converter?

Answer 40

Modern cars have a catalytic converter to help reduce the production of toxic gases.

Catalytic converters use a platinum and rhodium catalyst with a high surface area. This increases the rate of reaction of carbon monoxide and unburnt fuel from exhaust gases with oxygen from the air. The product from this is carbon dioxide and water, which is less harmful to the environment. The catalysts are designed to work best at the high temperatures found in the engine.