2.3 – physical and chemical properties of matter

2.3 – Physical and Chemical Properties of Matter

Every fire needs the same three components: fuel, oxygen gas, and heat

In a campfire:◦ The fuel is the wood, wood is rich in carbon◦ The carbon reacts with oxygen in the air, only if

the air can reach the carbon (which is why the log is split into splinters called kindling, so more carbon is exposed to the air)

The Chemistry of a Campfire

When lighting a fire, extra oxygen is sometimes needed (which is why blowing lightly on the embers helps, as long as you don’t blow the heat away)

Combustion releases heat, which is why there is no need to keep relighting the flame.◦ Combustion: a chemical change producing heat

and light

The Chemistry of a Campfire

Burning a log produces new substances: ◦ carbon dioxide that blows away◦ Ash that doesn’t burn

A campfire produces gas (carbon dioxide) and heat!

A campfire is a chemical reaction

In a physical change, a substance may change state (ie: ice cream melting), but the substance itself does not change.

In a chemical change, new substances are formed. We look for indicators, such as heat produced, gas produced, colour change, etc… (we will learn more about this soon!)

Physical Change vs. Chemical Change

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A physical property describes a characteristic of a substance that can be observed or measured.

Example: the melting point of something is a physical property. It can be measured.

Physical Properties

Water freezes and melts at 0°C

Water expands when it freezes◦ Good: Ice floats on water, making life still possible

in winter in lakes◦ Bad: Causes cracks and potholes in roads

Physical Properties of Water

Lustre – shiny or dull Colour Transparency – how see-through it is Mass Volume Density Conductivity Hardness Etc……

Observing Physical Properties

A substance may change appearance (such as changing state or size), but a new substance is not formed.

Eg: Water turning to ice, chopping wood

A physical change is reversible!

Physical Change

A chemical property describes the ability of a substance to change into a new substance or substances

Chemical properties include:◦ How a substance interacts with other substances◦ How it reacts to heat or light

Chemical Properties

A chemical change always results in the formation of new substances

Examples:◦ Burning paper◦ Baking a cake◦ Mixing vinegar and baking soda together

A chemical reaction is the process in which a chemical change occurs

Chemical Changes

Evidence of a chemical change can include a great variety of changes, including:◦ Colour

Ex: A chemical change makes a banana ripe, changing from green to yellow

◦ Odour Ex: When milk goes sour, it gives off a gross smell

Evidence of a Chemical Change

◦ Temperature Ex: A chemical cold bag, or mitt warmers

◦ Production of light Ex: a firefly has a chemical called luciferin, which

glows when it reacts with oxygen

Ex: A glowstick, once you crack it and mix the chemicals a light is produced

Evidence of a Chemical Change

◦ Formation of a new solid inside a liquid Ex: Milk going sour, producing curds inside the liquid

◦ Production of gas Ex: Mixing baking soda and vinegar, look for bubbles

◦ Etc…

Evidence of a Chemical Change

Physical or Chemical?

Physical or Chemical?

Physical or Chemical?

Physical or Chemical?

Physical or Chemical?

Physical or Chemical?