Composition of MatterChap 3

Physical Properties of Matter• Characteristics observed or measured

without changing the identify of a substance.

• Shape, physical state, odor, boiling and freezing points, density, and color of that substance.

Physical ChangesA physical change occurs in a substance if there is

• A change in the state.• A change in the physical shape.• No change in the identity and composition of the

substance.

Examples of physical changes: • Paper torn into little pieces (change of size)• Copper hammered into thin sheets (change of

shape)• Water poured into a glass (change of shape)

Chemical PropertiesChemical properties describethe ability of a substance• To interact with other substances.• To change into a new substance.

Example:Iron has the ability to form rust when exposed to oxygen.

Chemical ChangesIn a chemical change, a new substance

forms that has• A new composition• New chemical properties• New physical properties

4 Ways to Separate a Mixture

1. Filtration

2. Distillation

3. Crystallization

4. Chromatography

Evidence of a Chemical Reaction1.Change in color2.Production of Gas or odor3.Formation of Heat4.Formation of Precipitate

Conservation of Mass

Mass reactants = Mass products

2 HgO 2 Hg + O2

216g 200g + 16g

Sample ProblemFrom a laboratory process designed to

separate water into hydrogen and oxygen gas, a student collected 10.0g hydrogen and 79.4g oxygen. How much water was originally involved in the process?

Sample ProblemA student carefully placed 15.6g sodium in a reactor supplied with an excess quantity of chlorine gas. When the reaction was complete, the student obtained 39.7g of sodium chloride. How many grams of chlorine gas reacted? How many grams of sodium reacted?

Sample ProblemA 28.0g sample of nitrogen gas combines completely with 6.0g of hydrogen gas to form ammonia. What is the mass of the ammonia formed?

Sample ProblemA substance breaks down into its component elements when heated. If 68.0g of the substance is present before it is heated, what is the combined mass of the component elements after heating?

Sample Problem12.4 grams of nitrogen are combined with 32.5g of oxygen. What mass of nitrogen oxide is formed?

Sample ProblemIf 122.7g of lithium fluoride are broken down into lithium and fluorine gas. The amount of lithium produced is 78.4g. How much fluorine gas was produced?

Law of Definite ProportionsA compound is always composed of the same elements in the same proportions by mass

Water H2O

H 1.0g x 2O 16.0g

Percent by Mass% Mass = Mass Element X 100

Mass CompoundThe percent by mass of each element in a compound remains constant even if the amount changes.

Analysis of Sucrose

Element Analysis by Mass Percent by Mass

Carbon 8.44g 42%

Hydrogen 1.30g 6.50%

Oxygen 10.26g 51.30%

Total 20.00g 100%

Analysis of a 20.oo g quantity of sucrose

Analysis of Sucrose 500gElement Analysis by Mass Percent by Mass

Carbon 211.0 g 42%

Hydrogen 32.5 g 6.50%

Oxygen 256.5 g 51.30%

Total 500 g 100%