Describe a substance based on its ability to change into a new substance with different different propertiesproperties

Does wood have a chemical property?

a piece of wood can be burned to create new substances (ash and smoke) with properties different from the original piece of wood.

– Flammability– Non-flammability– Reactivity with oxygen– Reactivity with acid– Reactivity with water

• (reactivity just means that when two substances get together, something can happen.)

• Chemical properties can be observed with your senses. However, chemical properties aren’t as easy to observe as physical properties.

• You can observe the flammability of wood only while the wood is burning

• You can observe the non-flammability of gold only when you try to burn it and it won’t burn

Why do cars rust??• Most car bodies are made from

steel, which is mostly iron• Iron has many desirable physical

properties, including strength, malleability, and a high melting point

• Iron also has many desirable chemical properties, including nonreactivity with oil and gasoline.

• However, one unfavorable chemical property of iron is its reactivity with oxygen. When iron is exposed to oxygen, it rusts.

• Because paint doesn’t react with oxygen, it provides a barrier between oxygen and the iron in the steel. If the paint chips, it exposes the iron in the car’s body to oxygen. The

iron will rust and eventually crumble away.

• Some bumpers are rust free because they are coated with a barrier of chromium or stainless steel, which is nonreactive with oxygen.

• Car manufacturers also use plastic products to reduce the effects of rust.

• A new car contains up to 180 kilograms of plastic. Back in 1970, cars contained only about 27 kilograms of plastic.

• Can you think of areas in a car where plastic is used?

• What is the advantages of using plastic parts instead of metal parts.

• You can describe matter by both physical and chemical properties.

• The properties that are most useful in identifying a substance are its characteristic properties.

• Scientists rely on characteristic properties to identify and classify substances.

• The following table compares both physical and chemical properties of some common substances.

Comparing Physical and Chemical Properties

Substance Physical Property Chemical Property

Helium Less dense than air Nonflammable

Wood Grainy texture Flammable

Baking soda White powder Reacts with vinegar to produce bubbles

Powdered sugar White powder Does not react with vinegar

Rubbing alcohol Clear liquid Flammable

Red food coloring Red color Reacts with bleach and loses color

Iron Malleable Reacts with oxygen