Chapter 3Physical and Chemical

Properties

Physical and Chemical Changes

Physical Properties

• Physical properties can be observed or measured without changing the composition of matter.

• Physical properties include: appearance, texture, color, odor, melting point, boiling point, density, solubility, and many others.

What do you think this is?

What do you think this is?What physical properties can be “observed”?

Physical Properties

• Physical State: Solid

• Description:

– Grayish metal.

• Melting Point: 922K 649°C 1200°F Boiling Point: 1363K 1090°C 1994°F

• Density: 1.738g/cm3

• Specific Heat: 1.02J/g∙°C

Chemical Properties

• Chemical properties of matter describe how a substance reacts to form a new substance(s).

Chemical Properties

• “Reactivity” is really the only chemical property. Anything that describes how a substance reacts is a chemical property.

• For example hydrogen is explosive.

Chemical Properties

•Reacts slowly with water to form a base.

•Reacts violently with acid forming hydrogen gas.

•Reacts with carbon dioxide producing an intense light.

Chemical Properties

Magnesium reacting with dry ice.

Magnesium and Carbon Dioxide

Physical Changes

• A physical change takes place without any changes in composition.

• The same element or compound is present before and after the change.

Chemical Changes or Reactions

• Chemical changes result in one or more substances of entirely different composition from the original substances.

• The atoms at the start of the reaction are rearranged into new substances.

PHYSICAL CHANGE CHEMICAL CHANGE

Do not change the chemical makeup of the changed

material (no new substance formed)

Result in a new material with a different chemical makeup

being formed (new substance formed)

Change only the physical properties of a material

Change both physical and chemical properties of a

material

relatively simple to reverse very difficult to reverse

Look to be fairly simple changes Look more dramatic

Not Likely to be accompanied by changes in color, temperature,

state (unforced), or smell.

Often accompanied by change in color, temperature, state ( unforced), or smell.*

Sucrose (sugar) reacts with sulfuric acid.

• Sucrose (sugar) reacts with sulfuric acid creating carbon and water.

• C12H22O11 + H2SO4 → different substances

Changes of State are physical changes but can accompany a chemical change.

• Physical Change • Chemical Change

Precipitate

Precipitate

• A solid insoluble substance that forms when solutions are mixed.

Separation Techniques for Mixtures

• Distillation

• Fractional Crystallization

Distillation

• Distillation is used to separate parts of a mixture that have different boiling points.

• Distillation is the process of heating a liquid until it boils, capturing and cooling the resultant hot vapors, and collecting the condensed vapors.

Fractional Crystallization

• Separates different solutes from a solution based on differences in their solubility.

• A process by which a chemical compound is separated by crystallization.

What is the solubility of KNO3 at 80ºC?

≈ 160g KNO3 per 100 g water

At what temperature is the solubility of KBr equal to 60g/100g H2O?

≈ 10°C

Homework

• Chapter 3 Worksheet 3-1