Chapter 2 - Matter, Changes, and Energy

Definitions:

• Chemistry - Study of matter and the changes it undergoes
• Matter - anything that has mass and occupies space
• Element - most basic form under ordinary conditions, can not be broken down
• Compound - a substance composed of two or more elements

Physical properties of matter

States - gas, liquid, solid

1. Solid - has definite shape and definite volume
2. Liquid - have definite volume but no definite shape
3. Gas - no definite volume or shape

Density

Density = Mass per unit volume = Mass/Volume

Specific Gravity

Ratio of the density of an object compared to density of water

Specific gravity = density of substance/density of water

Chemical properties Vs. Physical properties

• Chemical properties describe how one substance reacts with other substances
• Physical properties are properties that can be observed and specified without reference to any other substance.

Mixtures

Two Types of mixtures

1. Heterogeneous mixture - non uniform, containing two or more phases
2. Homogenous mixture - uniform, one phase

Solution - a homogenous mixture with one liquid phase

Compare pure water, pure NaCl and salt water

• Boiling point elevation
• Freezing point depression
• Density

Alloy - a homogenous mixture of metallic elements in solid phase

Energy - the ability to do work

1. Light (or radiant) energy
2. Chemical energy
3. Heat energy
4. Mechanical energy
5. Electrical energy

Chemical Reaction Energy

1. Releases heat - EXOTHERMIC
2. Absorbs heat - ENDOTHERMIC

Types of Energy

1. Potential energy - energy available because of position or composition
2. Kinetic energy - energy resulting from motion

Specific Heat - the amount of heat required to raise the temperature of one gram of a substance one degree Celsius. (Specific heat does not change with the amount of substance)

Calorie - the amount of energy required to raise one gram of water one degree Celsius

SI Unit of heat - joule

1 cal = 4.184 joule (J)

Specific heat of water = 4.184 J/g × ° C (joules per gram per degree Celsius)

For any substance:

Law of Conservation of mass - matter is neither created nor destroyed mass at beginning of reaction = mass at the end of a reaction

Law of Conservation of energy - energy cannot be created or destroyed but only transformed (energy in the universe is constant)