CC: CHEMICAL CHANGES (CHEMICAL REACTIONS BASICALLY)

What changes are there?????????

• Physical change

• Chemical change

Physical change (e.g. chewing)

• No new substance is formed

• Properties of substances do not change

• No heat/little heat is taken in or out

Chemical change (e.g. baking / cooking, chewing but with digestive juices)

• New substances is formed

• Properties of substances are different from reactants

• Heat/light energy may be taken in or given out 

A+B (reactants) → C+D (products)

HOW do you know chemical reaction has taken place?

• Colour change

• heat/ light given off

• Odour given off

• Effervescence

• Precipitate formed (solid forming in liquid)

Chemical changes occur due to…?

1. Interactions between different kinds of matter (mixing)

2. Interactions between matter and energy (heat, light, electricity)

Interactions between different kinds of matter (mixing)

1. Neutralisation

2. precipitation

Interactions between matter and energy (heat, light, electricity)

1. Combustion (heat)

2. Decomposition (heat, light electricity)

3. Electrolysis (electricity)

TYPES OF CHEMICAL REACTIONS

1. Involving acids and alkalis

   • Acids and alkalis chapter

2. Precipitation

3. Oxidation

4. Combustion

5. Decomposition

6. Other reactions in daily life

Precipitation

1. Salt solution + another salt solution

2. Salt solution + alkali

   • Process in which an insoluble solid (precipitate) is formed when two solutions are mixed

Oxidation

• A substance may react with oxygen to form a new substance (substance is oxidized)

1. Rusting 

2. Respiration

Combustion

• The burning of substances in oxygen [basically every equation need oxygen] (heating required)

  • Energy is released usually in the form of heat and light

1. Combustion of magnesium

2. Combustion of coal

3. Combustion of sulfur

4. Combustion of hydrogen

5. Combustion of methane ( cow fart contains methane)

Decomposition

• Process whereby a compound breaks down into two or more substances

1. Decomposition

2. Decomposition by light

3. Thermal decomposition

4. Electrolysis (using electricity to break down a compound)

Other reactions in daily life

1. Photosynthesis

2. Acid rain formation

Extra process:

• Cooking

• Decay of food

• Electroplating 

Cooking

• Denatured (break down bonds)

• Coagulation (forming new structures)

Decay of food

Breaking down organic matter into simpler substances

Electroplating

Process of depositing a layer of metal on another substance using electrolysis

BENEFITS OF CHEMICAL CHANGES:

• Releases nutrients back to earth

• Manufacturing stuff like detergent and fertilisers

• Metals are obtained

• Synthesis of medicine 

• Cooking

• Electroplating

HARMFUL EFFECTS OF CHEMICAL CHANGES:

• Rusting causes structures to corrode → unsafe

• Decomposition leads to wastage of food and resources

• Combustion release air pollutants (cars and factories)

• Some air pollutants cause acid rain

SUMMARY: Chemical changes occur due to interactions between matter and/when:

• Mixed

• Heat

• Light

• electricity