3.2 P ROPERTIES AND C HANGES OF M ATTER 3.3 E NERGY Chemistry

Properties of Matter Introduction Chemists interested in characteristics that can be tested and observed Reliance on color, state (phase) – solid / liquid / gas, temperature, volume, mass, texture Some characteristics that cannot be directly observed

Physical and Chemical Properties Two basic types of properties used to describe or identify matter Physical properties – can be observed without changing identity of substance Water to steam Steam vapor form of water Chemical properties – only observed when substance changed into new substance Methane and oxygen to carbon dioxide and water New substances with different properties

Physical and Chemical Changes Physical changes – no change in identity of substance Change of state Separation of mixture Physical deformation Making solutions Chemical changes – one substance turned into another substance

Energy Introduction Energy complicated Light bulb vs. heating pad Lights Brushing teeth Making lunch Transportation to school

Types of Energy: Kinetic and Potential Energy – ability to do work or cause change Many different forms Kinetic – associated with motion Potential – stored energy that remains available until we choose to use it

Kinetic Energy Amount determined by mass and speed Heavier, faster = greater kinetic energy Common and easy to observe Only available when something moving When not effective?

Potential Energy Frequently used for power Batteries Many different storage methods – may be hard to recognize Often use chemical potential energy in chemistry Chemical potential energy – energy stored in atoms, molecules, and chemical bonds Different amounts in different chemicals Dependent on position and composition

The Law of Conservation of Matter and Energy Energy constantly changing from one type to another Law: energy cannot be created or destroyed Energy like money – can be exchanged or changed from one form to another, but never goes away E.g. throwing a ball

The Law of Conservation of Matter and Energy Energy and matter actually interchangeable Law – the total amount of mass and energy in the universe is conserved (does not change) Chemistry generally treats matter and energy separately.

Heat and Work Energy “use” actually transfer from one location to another Energy transferred as heat or work

Heat Heat – energy transfer from object at higher temperature to object at lower temperature E.g. heating pot from bottom Hot objects lots of energy that is transferred to colder objects when in contact Domino effect

Work Force (push or pull) applied over distance Not measure of effort No movement = no work