Properties of Matter and Derived Units

1.3 Properties of Matter

Physical vs. Chemical Properties

· Physical properties: Measured without changing the substance (e.g. color, density, odor, melting point).

· Chemical properties: Describe how substances react or change to form different substances (e.g. hydrogen burns in oxygen).

· Intensive properties: Do not depend on the amount of substance present (e.g. temperature, melting point); give an idea of the composition of a substance.

· Extensive properties: Depend on quantity of substance present (e.g. mass, volume).

Physical and Chemical Change

· Physical change: Substance changes physical appearance without altering its identity (e.g. changes of state).

· Chemical changes (or chemical reactions): Substances transform into chemically different substances (i.e. identity changes, e.g. decomposition of water, explosion of nitrogen triiodide).

The Scientific Method

The scientific method: guidelines for the practice of science.

· Collect data (observe, experiment, etc.)

· Look for patterns, try to explain them and develop a hypothesis.

· Test hypothesis; refine it.

· Bring all information together into a scientific law (concise statement or equation that summarizes tested hypotheses).

· Bring hypotheses and laws together into a theory. a theory should explain general principles.

1.4 Units of Measurement

· Many properties of matter are quantitative.

· A measured quantity must have BOTH a number and a unit.

· The units most often used for scientific measurement are those of the metric system.

SI Units

· 1960: all scientific units use Systeme International d’Unites (SI Units)

· There are seven base units.

· Smaller and larger units are decimal fractions or multiples of the base units.

Length and Mass

· SI base unit of length = meter (1 m = 1.0936 yards).

· SI base unit of mass (not weight) = kilogram (1 kg = 2.2 pounds).

§ Mass is a measure of the amount of material in an object.

Temperature

· Scientific studies use Celsius and Kelvin scales.

· Celsius scale: Water freezes at 0 oC and boils at 100 oC (sea level).

· Kelvin scale (SI unit)

§ Water freezes at 273.15 K and boils at 373.15 K (sea level).

§ Based on properties of gases.

§ Zero is lowest possible temperature (absolute zero).

§ 0 K = -273.15 oC.

· Fahrenheit (not used in science)

§ Water freezes at 32 oF and boils at 212 oF (sea level)

§ Conversions:

oF - 32 = 1.8 oC K = oC + 273.15

Derived SI Units

· These are formed from the seven base units.

· Example: velocity is distance traveled per unit time, so units of velocity are units of distance (m) divided by units of time (s): m / s

Volume

· Units of volume = (units of length)3 e.g. m3

· This unit is unrealistically large, so we use more reasonable units:

§ cm3 (also known as mL or cc (cubic centimeters))

§ dm3 (also known as liters, L)

§ Important: the liter is not an SI unit.

Density

· Used to characterize substances.

· Density is defined as mass divided by volume.

· Units are usually g / cm 3.

· Originally based on mass (the density was defined as the mass of 1.00 g of pure water).