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. FlammabilityReactivity

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