Chemical Reactions

Question 1

Chemical change/reaction

• How do you know chemical changes are occurring?
• What things are chemical changes?

Answer 1

• new substances are made
• occur due to chemical reactions
• bonds are broken
• Change of colour
• Fizzing
• Change temperature
• Change in smell

Examples:

• Baking a cake
• Burning paper

Question 2

Physical Changes

• How do we know physical changes are occurring?
• What things are physical changes?

Answer 2

• No new substance made
• Bonds are not broken
• Easy to reverse

Examples:

• Boiling water
• Melting chocolate
• Smashing a glass

Question 3

Test for Hydrogen

Answer 3

Hydrogen is a gas given off in reactions between a reactive metal and an acid we can test it with the squeaky pop test.

Squeaky pop test:
Place a lit spill into hydrogen
Result:
A pop noise is made and the hydrogen is visible - it looks like smoke

Question 4

Test for carbon dioxide

Answer 4

Carbon dioxide is a gas given off in reactions between a reactive metal carbonate and an acid. We can test for it with limewater. Colourless limewater becomes cloudy.

Limewater test:
Blow CO2 through a straw of limewater
Result:
The limewater begins to bubble then it turns cloudy

Question 5

Testing for oxygen

Answer 5

Oxygen is a gas given off in the breakdown of hydrogen peroxide. We can test for it with a glowing spill. Oxygen causes the spill to relight.

Glowing splint:
Place a glowing splint into oxygen
Result:
The splint is re-lit

Question 6

Testing for water

Answer 6

When cobalt chloride paper comes into contact with water, it goes from blue to pink.

Question 7

Conservation of mass

Answer 7

Mass of products = Mass of reactants

This is because no atoms are created or disappear in reaction, they are just moved about.

Question 8

Thermal decomposition

Answer 8

Thermal Decomposition is the breaking down of substances using heat.

Examples:

Copper carbonate—> copper oxide + carbon dioxide
Calcium carbonate—> calcium oxide + carbon dioxide

Question 9

Oxidation

Answer 9

A Metal being reacted with Oxygen

Magnesium + Oxygen ⇒ Magnesium Oxide
Mg + O2 -> MgO

Question 10

Complete combustion

Answer 10

•enough oxygen present

Fuel + oxygen -> water + carbon dioxide

Question 11

Incomplete combustion

Answer 11

•not enough oxygen

Fuel + oxygen ⇒ water + carbon monoxide + carbon

Question 12

Precipitation Reactions

Answer 12

Question 13

Soluble salts

Answer 13

ALL sodium salts - Na
ALL potassium salts - K
ALL ammonium salts -NH
ALL nitrates - NO
MOST sulfates - SO

Question 14

Insoluble salts

Answer 14

MOST carbonates - CO
MOST hydroxides - OH
MOST oxides - O
MOST lead compounds - Pb
MOST silver compounds - Ag
Barium Sulfate - BaSO

Question 15

Word equations

Answer 15

Examples:

• Sodium + chlorine —> Sodium chloride
• Tin + carbon + oxygen —> Tin carbonate
• Magnesium + chlorine —>magnesium chloride

Question 16

Why are masses increased after you burn something in oxygen?

Answer 16

Because you need oxygen for something to burn, oxygen atoms are added.

Question 17

Why does mass appear to decrease during thermal decomposition reactions?

Answer 17

Because gases are released into the atmosphere and they disperse.

Question 18

The products that form when a fuel burns

Answer 18

• carbon dioxide
• water

Question 19

Reaction of different acids with different metal carbonates

Answer 19

• When acids react with carbonates, a salt, water and carbon dioxide are made.
• The carbon dioxide causes bubbling during the reaction, which is observed as fizzing.
• It can be detected by passing the gas through limewater, which will go cloudy.

Question 20

Balancing equations Key information:

Answer 20

• You cannot change small numbers
• You can put numbers in front of elements and compounds