Science - Physical and Chemical Changes

Physical Change

A change where no new substance is formed, usually done by heat or force

• Sugar dissolving in tea

• Ice melting

• Chopping wood

Usually can be reversed easily

Chemical Change

A change in which a new substance is formed, cannot be reversed easily

• Burning paper

• A nail rusting

• Acid reacting with a base

Difference between physical and chemical changes

Physical Change

• No new substance formed

• Often no heat change involved

• Can be reversed easily

Chemical Change

• New substance formed

• Very difficult or impossible to reverse

• Heat is always needed or produced

Describe an experiment that shows if mass changes during a physical change

• First you measure a block of ice

• Then you melt it in a sealed container

• Next you weigh the water leftover

• The masses should be the same as there is no loss of mass during the change

Describe an experiment that shows if mass changes during a chemical change

• Get a flask, balloon, water and an effervescent tablet

• Then pour the water into the flask

• Weigh all the apparatus

• Put the tablet into the water and then quickly put the balloon over the flask

• After the reaction is complete, weigh all the items again

• The masses combine should be nearly the exact same but a little weight is lost in the time when you put on the balloon as the gas escapes

Law of the conservation of mass

Mass is neither created nor destroyed but simply moves from one form to another

Matter

Anything that has space and mass (solids, liquids and gases)

Particle theory

All physical matter is composed of tiny, constantly moving particles that have spaces between them,

Properties of a solid

• Definite Shape

• Definite Volume

• Cannot be compressed

• Cannot flow

How are particles set up in a solid?

The particles that make up solids are held very closely together

They cannot move freely - but can vibrate

Properties of a liquid

• No definite shape

• Fixed volume

• Cannot be compressed

• Can flow

How are particles set up in a liquid

Particles in a liquid are a bit more free than solids and that allows them to change shape and flow

Properties of gases

• No definite shape

• No definite volume

• Can be compressed

• Can flow

How are the particles in gases set up

Particles in a gas are so spread out that they can be compressed

Diffusion

The movement of molecules from an area of high concentration to an area of low concentration (food colouring mixing in water, air freshener spreading in a room)

Boiling

A rapid, bulk change throughout the liquid at a specific temperature (boiling point), forming visible bubbles, like water cooking on a stove, requiring external heat.

The particles in a liquid get heated up really fast and spread out turning the liquid into a gas

Evaporation

A slow, surface-level liquid-to-gas change at any temperature, like a puddle drying, occurring without bubbles

The particles in a liquid get heated up slowly and spread out turning the liquid into a gas

Melting

Melting is the process from which a solid turns into a liquid as a result of heat. The particles get spread out turning into a liquid

Freezing

The process in which a liquid turns into a solid as a result of a loss of heat. The particles slowly pack back together to form a solid

Condensing

The process in which a gas turns into a liquid as a result of a loss of heat. The particles cool down and go closer together but don’t fully pack together and turns into a liquid

Mixture

Made up of two or more substances mingled together but not chemically combined (saltwater, tea, coffee)

Filtration

Used to separate an insoluble solid and a liquid (such as soil and water)

Evaporation experiment

Used to separate a soluble solid and a liquid using heat (saltwater, tea and sugar)

Distillation

Used to separate substances which have different boiling point

Chromatography

A technique used to separate a mixture of dyes in ink based on their solubilities

Solute

The substance that dissolves

Solvent

The substance that the solute dissolves in

Solution

Solute + Solvent

Soluble

Name given to substances that dissolve in a solvent