PHYSICAL AND CHEMICAL PROPERTIES

Sections 2.2 and 2.3

What is a Physical Property?

Any characteristic of a material that can be observed or measured without changing the composition of the substances in the material. Viscosity, conductivity, malleability,

harness, melting and boiling points, density, and temperature are just a few examples.

Viscosity

The tendency of a liquid to keep from flowing- its resistance to flowing.

The higher the viscosity of a liquid, the slower the liquid moves.

When a substance is heated, the viscosity of that substance lowers.

Conductivity

A material’s ability to allow heat to flow.

Materials with a high conductivity are called conductors.

Malleability

The ability of a solid (metal) to be shaped without breaking.

Hardness, Melting & Boiling Points

To test hardness of material, you see which material can scratch the other.

Melting Point: The temperature at which a substance changes from a solid to liquid.

Boiling Point: The temperature at which a substance boils.

Density

Density is a ratio of the mass of a substance to its volume d=m/v

Objects made out of the same material have the same density.

Density can be used to test the purity of a substance.

Using Properties to Separate Mixtures

Filtration: A process that separates materials based on the size of their particles by using a strainer or filter.

Distillation: A process that separates the substance in a solution based on their boiling points.

Physical Changes

Occurs When some of the properties of a material change, but the substances in the material remain the same.

Some physical changes can be reversed. Freezing, melting, then

freezing water again

What is a Chemical Property?

Any ability to produce a change in the composition of matter.

Can only be observed when the substances in a sample of matter are changing into different substances.

Examples

Flammability The material’s

ability to burn in the presence of oxygen.

Lighting a candle

Reactivity How readily a

substance combines chemically with another substance.

Oxygen reacts easily with most elements. When oxygen reacts with iron and water rust forms.

Flammability Reactivity

Recognizing a Chemical Change

A chemical change occurs when a substance reacts and forms one or more new substances.

Three common types of evidence: Change of Color Production of Gas Formation of a Precipitate

Any solid that forms and separates from a liquid mixture.

Is it Chemical or Physical?

Don’t be fooled! A color change or production of gas doesn’t

always mean that a chemical change has taken place.

Ask yourself this: Are different substances present after the

change takes place? If you answer “no” then it’s a physical change If you answer “yes then it’s a chemical change