REVERSIBLE CHANGES:
When materials go through a reversible change, they can be changed back into their original form.
CHANGES OF STATE:
Changes in state of matter are reversible:
example:
- when water is cooled to 0 degree Celsius, it freezes and changes into ice. It is changed from liquid state to solid state. When ice gains heat and melts, it changes from solid state back to liquid state.
Melting ice (video)
- When we heat a block of butter, it melts, changing from solid state to the liquid state. When it cools, it hardens and changes from liquid state back to the solid state.
- When some salt is added to water, the salt dissolves completely in the water to form a solution. This change is reversible because the dissolved salt can be recovered by evaporating the liquid from the solution.
NON-REVERSIBLE CHANGES
When materials go through a non-reversible change, they cannot be changed back into their original form. Chemical changes are usually non-reversible.
- Burning of materials
when paper is burned,it goes through a chemical change to form ash. Ash that is formed cannot be changed back into paper.
- Cooking
When an egg is cooked by heating, it goes through a chemical change and cannot be changed back into a raw egg.
- Mixing cement with water
When cement is mixed with water and other substances, a new material, concrete, is formed. Concrete cannot be changed back into cement and water because a chemical change has taken place.
FACTORS THAT CAUSE ROTTING OF WOOD:
What causes the rotting of wood?
The rotting of wood is a non-reversible change it takes place when there is:
- wood rot fungi
- moisture
When wood is exposed to moisture in the air, it becomes moist. Moist wood is home wood rot fungi.
Wood rot fungi attack wood cells which cause the wood to become porous and crumbly.
Factors that cause rusting
What causes the rusting of metals?
Rust is a layer of reddish-brown substance that is formed on metals such as iron and steel. Rusting is the formation of rust on metals.
The rusting of metals is a non-reversible change. It takes place when there is:
- oxygen
- moisture
When a metal is exposed into the air, it combines with oxygen and moisture. As a result,rust slowly forms.
FACTORS THAT CAUSE DECOMPOSITION
What cause decomposition of dead matter and animal waste?
Decomposition is the breaking down of dead matter that was once alive and animal waste such as faeces into simple substances such as minerals, water and carbon dioxide.
Decomposition is a non-reversible change. It takes place in the presence of:
- decomposers
- oxygen
- moisture
- warmth
Decomposers need oxygen, moisture and warmth to live and grow.
EFFECTS OF CHANGES IN MATERIALS ON THE ENVIRONMENT:
What are some good and bad effect of changes in materials on the environment?
GOOD EFFECTS OF CHANGES IN MATERIALS
Some changes in materials have good effects on the environment.
RETURN OF MINERALS, WATER AND CARBON DIOXIDE TO THE EARTH
Minerals, water and carbon dioxide are returned to the environment when dead matter and animal waste decompose minerals are returned to the environment when dead matter and animal waste decompose. Minerals are returned to the soil as nutrients to be used again by plants.Carbon dioxide which is returned to the air ensures that the amount of oxygen and carbon dioxide in the air remains balanced.Decomposition also ensures that the earth is not covered by dead matter and animal waste
CREATION OF BIODEGRADABLE MATERIAL
Plant starch can be changed into a type of plastic called bioplastics when it is mixed with water and some other substances. Bioplastics can be used as a material to make food packaging and utensils.Unlike other types of plastics, bioplastics are biodegradable and thus unlikely to cause harm to the environment.
BAD EFFECTS OF CHANGES IN MATERIALS
Some changes in materials have bad effects on the environment.
AIR POLLUTION air pollution video
The burning of materials such as fuels releases harmful substances into the air. This causes air pollution which can lead to health problems.
DAMAGE TO EQUIPMENT
Rust formed on a metal can slowly eat away the metal and cause it to corrode.
The rusting of metals can be dangerous too.
Example:
- When important parts of a car such as the engine and car brake rust, they become weaker and may not work as well as before. When metals in electrical connections rust, they cannot conduct electricity well.
