States of matter and Phase Changes

Describing States of matter You may have noticed that some materials have a definite shape and volume, and some materials do not Materials can be classified as solids, liquids and gases based on whether their shapes and volumes are definite or variable. Shape and volume are clues to how the particles within a material are arranged

The kinetic theory Kinetic energy is the energy an object has due to motion The faster an object moves, the greater its kinetic energy is A ball thrown at 85mph has more kinetic energy than a ball traveling at 70mph

The kinetic theory of matter The kinetic theory of matter says that all particles of matter are in constant motion Particles of matter are always moving, ALWAYS This theory explains the behavior of solids, liquids, and gases

Solids Solids have recognizable shape and they all take up a certain amount of space The materials in these objects all exist in a solid state The molecules in a solid have a specific pattern

The behavior of solids Solids have a definite volume and shape This is because the particles in a solid vibrate around fixed locations The molecules in a solid are positioned in fixed locations relative to their neighbors Each atom vibrates within its location, but it never switches places with other atoms

Liquids Liquids have a definite volume, but not a definite shape A liquid always has the same shape as its container - water in a glass

The behavior of liquids A liquid takes the shape of its container because particles in a liquid can flow to new locations The volume of a liquid is constant because forces of attraction keep the particles close together - H20 molecules attract to one another

Gases Gas neither has a definite shape nor a definite volume A gas will take on the shape of its container The molecules in a gas are constantly moving and are not arranged in a particular pattern

The behavior of gases The particles of a gas are NEVER at rest At room temperature, the average speed of the particles in a sample of gas move at about 1600km/hr Atoms move in a straight line until they bump into one another, then their direction is changed *Demo*

The kinetic Theory of gases The constant motion of particles in a gas allows a gas to fill a container of any shape or size Particles in a gas are in constant, random motion The motion of one particle is unaffected by the motion of other particles unless the particles collide Forces of attraction among particles in a gas can be ignored under ordinary circumstances

PHASE changes A phase change is the reversible physical change that occurs when a substance changes from one state of matter to another Melting Freezing Vaporization Condensation Sublimation Deposition

Melting When a solid experiences a phase change into liquid form Every substance has a unique “melting point” at which they turn to liquid

Freezing The phase change in which a liquid changes into a solid Not all liquids freeze in cold temperatures, some liquids are able to freeze at room temperature

Vaporization The phase change in which a liquid turns into a gas Occurs at a substance’s “boiling point”

condensation The phase change in which a substance changes from a gas or vapor into a liquid Dew on the grass in the morning Water droplets forming on the outside of your cup on a hot day

sublimation The phase change in which a substance changes from a solid to a gas without changing to a liquid first - Dry Ice

deposition The phase change in which a gas or vapor changes directly to a solid without first changing into a liquid Ice on car windshield

Temperature and phase changes One way to recognize a phase change is by measuring the temperature of the substance as it is heated or cooled The temperature of a substance does not change during a phase change

Energy and phase changes Energy can either be absorbed or released during a phase change The energy most commonly used in phase changes is heat energy The absorption of energy during a phase change is called an endothermic change The release of energy during a phase change is called an exothermic change

Endothermic Changes Endothermic changes happen when energy is absorbed by a system Water evaporating is an example of an endothermic change

Exothermic Changes An exothermic reaction occurs when energy is released by a system into its surroundings A melting ice cube is an example of an endothermic change