Chemical Reactions

Question 1

A chemical reaction

Answer 1

A chemical reaction is a process that happens when two or more chemical substances are put together to make a new substance

Signs of a chemical reaction:
A gas is given off
Possible colour change
Change in state
Change in temperature 
The reaction is irreversible 

Rusting of iron
Burning if petrol
The hardening of glue

Question 2

Chemical substances

Answer 2

Carbon dioxide- extinguishes a flame and also turns lime water cloudy.

Hydrogen- burns with a squeaky pop.

Oxygen- relights a glowing splint.

Nitrogen- puts out a flame but doesn’t affect lime water.

Question 3

Element

Answer 3

An element is a substance that can’t be broken down into a simpler one by a chemical reaction.

An element is a substance consisting of electrons all with the same atomic number

They are chemically the simplest substances

The number of electrons in an element is the same as the number of protons it has

The number of protons + the amount of neutrons in an element is called the mass number

The number of protons or electrons in an element is called the atomic number

Elements are made up of particles called atoms

All the atoms of one element are identical

The atoms of one element are different to the atoms of any other element

Atoms of one element can join with atoms of other elements to form compounds

Question 4

Solid, Liquid and Gas

Answer 4

Solid- close together, regular pattern. Vibrate on spot (low energy).

Liquid- close together, random arrangement
Move around each other.

Gas- far apart, random arrangement. Move quickly in all directions (high energy).

Question 5

Rate of reaction

Answer 5

How to speed up a chemical reaction:

• Have a substance with high concentration
• Have a big surface area
• Small particle size(solid)
• Have a substance or liquid with high temperature
• Adding a catalyst
• Stir it

Question 6

Catalyst

Answer 6

A catalyst is a substance which speeds up the rate of reaction

Catalysts cannot be used up and can be re-used.

Enzymes are biological catalysts

• Reagent A connects onto the catalyst
• Reagent B connects onto the catalyst
• Reaction occurs on catalyst
• The product of the chemical reaction leaves the catalyst.

A catalyst helps reactants collide to make a chemical reaction
You have amylase in your saliva

A catalyst helps particles collide more accurately to form chemical reactions

Question 7

Rate of reaction

Answer 7

Rate of reaction=

no. of bubbles divided by the time period

Question 8

The atom

Answer 8

The nucleus in an atom contains protons and neutrons.

An atom is made up of particles

Then electrons are found in the outer shells and surrounding nucleus.

Atomic number= no. of protons or no. of electrons

Proton- positive charge ( mass 1)
Neutron- neutral charge ( mass 1)
Electron- negative charge( mass 0)

Question 9

Drawing graphs

Answer 9

Line graphs can be used to compare changes over time for one variable. ( continuous)

Bar graphs are used to compare things between different groups or to track changes over time. ( non- continuous or discrete)

Question 10

Atomic and mass number

Answer 10

The number of neutrons = atomic mass no. - atomic no.

Question 11

Chemical properties

Answer 11

Chemical properties are like the characteristics of an element, and they differ for each one.

Properties include:
Melting and boiling points
State at room temperature(solid, liquid or gas)
Conductivity(the ability to carry the flow of an electric current- a flow of electrons)

Solubility( a measurement of how much of much of a substance will dissolve in a liquid)
Reactivity(the ability to take part in chemical reactions)

Question 12

Compounds

Answer 12

Metal and non-metal atoms give/ receive electrons to form ionic bonds.

2 non-metals share electrons to form covalent bonds.

The types of compounds:
Linear
Bent
Trigonal 
Tetrahedral 

The chemical formula tells us how many of each atom there are in a molecule. E.g. H2O there are 2 hydrogen and 1 oxygen.

Question 13

The periodic table

Answer 13

Group 1- alkali metals (apart from hydrogen)

Group 2- Alkaline earth metals

Group 7- halogens (apart from Uus)

Group 8- noble gases

Question 14

Molecules and particles

Answer 14

An atom is just that, made from protons, neutrons and electrons.

A molecule is a group of atoms bonded together via ionic, metallic or covalent bonding.

Question 15

Acid and Alkalis

Answer 15

Acid + alkali -> salt + water

Salts of different acids
Acid | Salt formed
—————————————————————
Hydrochloric Chloride
Nitric Nitrate
Sulphuric Sulphate
Phosphoric Phosphate

Question 16

Acids

Answer 16

Coca Cola
Lemon juice
Battery acid
Vinegar 
Hydrochloric acid

Question 17

Alkalis

Answer 17

Toothpaste 
Bleach
Soap
Cilit bang 
Drain cleaner

Weak alkali
Baking powder
Milk of magnesia

Question 18

Ph indicator

Answer 18

A Ph indicator is a substance which has one colour when added to an acidic solution and a different colour when added to an alkaline solution.

Question 19

Non- metal oxides

Answer 19

Carbon dioxide
Sulphur dioxide
Nitrogen oxide

When non-metal oxides are mixed with water, they produce an acidic solution.

Carbon dioxide dissolves in water to produce carbonic acid.

Question 20

Metal oxides

Answer 20

Metal oxides form alkali solutions

E.g:
Sodium oxide + water -> sodium hydroxide + H2(g)

Magnesium oxide + water -> magnesium hydroxide solution

Potassium oxide + water -> potassium hydroxide

Question 21

State symbols

Answer 21

(s) = solid
(g) = gas
(l) = liquid
(aq) = aqueous solution(dissolved in water)

Question 22

Neutralisation reactions

Answer 22

• Neutralisation is when an acid and an alkali react together to form a neutral solution.
• Increasing the pH of an acid (reducing pH of an alkali) helps reduce its corrosive(destructive) properties.
• This can be done by diluting the acid or neutralising the acid.
• Adding a chemical called a base is a way of neutralising an acid.

There are 3 types of base:

• Metal hydroxides
• Metal oxides
• Metal carbonates

Question 23

Naming compounds

Answer 23

• If the compound ends in -ide then it usually contains only two elements.
• If the compound name ends in -ate or -ite then it contains three or more elements one of which is always oxygen.

The element to the furthest left in the periodic table comes first.

Question 24

Neutralisation and bases

Answer 24

Acids can be neutralised by compounds called bases. Base include alkalis(metal hydroxides), metal oxides and metal carbonates. When acids and bases react together, neutralisation reactions take place. This results in the pH moving towards 7.

During neutralisation, an acid’s pH will increase towards 7.

During neutralisation a base’s pH will decrease towards 7.

Question 25

When a solid is formed

Answer 25

When two solutions mix and a solid is formed, the solid is called a precipitate.

A precipitate is an insoluble solid formed from two liquids reacting. Milk turning sour produces a solid.

Question 26

Exothermic and endothermic

Answer 26

An exothermic reaction is one in which heat energy is given out to the surroundings. The temperature rises.

An endothermic reaction is one in which heat energy is taken in from the surroundings. The temperature falls.

Question 27

Alkali metals
Halogens
Noble gases

Answer 27

The alkali metals are a group of very reactive metals. They are so reactive that they even react with water.

The halogens are very reactive non-metals. This group contains elements in all three states of matter.

The noble gases are very unreactive non-metals.

Question 28

Acids and metal carbonates

Answer 28

Acids can also be neutralised by metal carbonates. In these neutralisation reactions, there are three products:
A salt, water and carbon dioxide gas.

When a metal carbonate is added to an acid, carbon dioxide gas is given off.

Question 29

Combustion

Answer 29

When a metal burns in the air, a compound of the metal and oxygen known as a metal oxide is formed. A more scientific name for burning is combustion.