Chemistry! 9/22/09 Properties of Matter. Measuring matter Mass: amount of matter. (kg, g, lbs) Volume: Space taken up in 3D (m 3, mL, cm 3, Liters)

Chemistry!

9/22/09

Properties of Matter

Measuring matter

Mass: amount of matter. (kg, g, lbs) Volume: Space taken up in 3D (m3,

mL, cm3 , Liters)

Types of properties

Extensive: length, mass, volume, weight. (change with amount of substance)

Intensive: density, reactivity, hardness, viscosity.

Changes in matter

Physical change: change in extensive properties.

Examples: cutting, expanding, deforming

Chemical change: change in intensive properties

Examples: mixing baking soda and vinegar, burning gasoline.

Signs of chemical change

Exothermic (reaction gives off heat) Endothermic (reaction needs heat

around it to happen) Color change

Physical or chemical change?

Physical or chemical change?

Physical or chemical change?

Physical or chemical change?

Physical or chemical change?

Volume Readings

Read the meniscus at eye level

Reading the meniscus

WATER prefers to adhere to the glass walls. Hg prefers to COHERE (sticks to

itself).

Cohesion vs. adhesion: a meniscus may be either concave or convex, depending on fluid.

Measuring Volume with water displacement

Phase Changes

Solid: Crystal structure,

Molecules held in place.

Liquid: molecules “slide” past each other

Gas: molecules repel away from each other, spread out.

Phase Changes

Solid: Definite shape,

definite volume.

Liquid: takes container shape,

definite volume.

Gas: takes container

shape and volume.

Temperature Scales:Farenheit

Water boils/condenses:

Water freezes/thaws:

Absolute zero:

212°

32°

-459.67°

Temperature Scales:Celsius

Water boils/condenses:

Water freezes/thaws:

Absolute zero:

100°

0°

-273.15°

Temperature Scales:Kelvin

Water boils/condenses:

Water freezes/thaws:

Absolute zero:

373.15 K

273.15 K

0 K

Temperature Scales:Celsius

1° F is “narrower” than 1° C.

Converting between Farenheit and Celsius: Scales start in different places.

An increase of 1° C = 9/5° F

F = 9/5C + 32

At 0° C : F = C + 32

Temperature Scales:Kelvin

Kelvin: “width” of 1 K same as 1° C.

0 K is absolute zero.

Significant Figures

How do I round this answer?

Significant figures: rules for rounding answers, writing measurements.

Significant Figures

300.123 g : very precise.

Precise measurements: more sig. figs.

300 g : not as precise.

6 s.f.

1 s.f.

Converted to pounds:

0.136136 lbs

0.1 lbs

Significant Figures: my mass

1 s.f.: 60 kg, 60000 g, 0.06 Mg,

0.00006 Gg, 6 x 10-8 Tg All the same thing!

Go back and measure more carefully:

2 s.f.: 63 kg, 63000 g, 0.063 Mg,

0.000063 Gg 6.3x 10-8 Tg

Rough measurement: 60 kg

3 s.f.: 63.2 kg, 63200 g, 0.0632 Mg, 0.0000632 Gg 6.32x 10-8 Tg

Significant Figures: my mass

5 s.f.: 63.205 kg, 63205 g, 0.063205 Mg,

0.000063205 Gg, 6.3205 x 10-8 Tg

4 s.f.: 63.20 kg, 63200 g, 0.06320 Mg, 0.00006320 Gg 6.320x 10-8 Tg

Significant Figures: the rules

Always count nonzero digits.

Count zeroes only when:

They come between non-zero digits (502 g)

If after decimal, they don’t change the value of the number if removed (e.g. 63.0 mL)