Physical Properties and Changes of Matter: States of Matter and Phase Changes

What is a solid?

A state of matter with definite shape and volume; particles tightly packed with strong intermolecular forces.

What is a liquid?

A state of matter with definite volume but no definite shape; particles close but able to slide past each other.

What is a gas?

A state of matter with no definite shape or volume; particles far apart with very weak intermolecular forces.

How do solids behave?

Particles vibrate in place, high density, not compressible.

How do liquids behave?

Particles slide and flow, moderate density, low compressibility, take shape of container.

How do gases behave?

Particles move freely and rapidly, lowest density, highly compressible, fill entire container.

What determines the state of matter?

Strength of intermolecular forces between particles.

Why are solids dense?

Particles are tightly packed with little space between them.

Why are gases least dense?

Particles are far apart with large empty space between them.

Why do liquids have moderate density?

Particles are close but not as close as solids.

What is compressibility?

How easily a substance’s volume can be decreased; gases compress most, solids least.

Why is ice less dense than water?

Ice forms a tetrahedral hydrogen-bond lattice that spaces molecules farther apart.

How do solid particles move?

They vibrate but stay in fixed positions.

How do liquid particles move?

They slide and flow past each other.

How do gas particles move?

They move rapidly, randomly, and spread apart.

What is melting?

Solid to liquid; requires heat; endothermic.

What is freezing?

Liquid to solid; releases heat; exothermic.

What is vaporization?

Liquid to gas; requires heat; endothermic; occurs at boiling point.

What is condensation?

Gas to liquid; releases heat; exothermic.

What is sublimation?

Solid to gas; requires heat; endothermic (example: dry ice).

What is deposition?

Gas to solid; releases heat; exothermic (example: frost formation).

What is an endothermic process?

Phase change that absorbs heat (melting, vaporization, sublimation).

What is an exothermic process?

Phase change that releases heat (freezing, condensation, deposition).

What is the melting point?

Temperature where solid ↔ liquid; same for melting and freezing.

What is the boiling point?

Temperature where liquid ↔ gas; same for vaporization and condensation.

How does temperature affect molecules?

Higher temperature = faster movement and farther spacing.

How does pressure affect molecules?

Higher pressure = pushes molecules closer together.

What is a phase diagram?

A graph showing which state of matter exists at different temperatures and pressures.

What is the triple point?

Temperature and pressure where solid, liquid, and gas all exist in equilibrium.

What is the critical point?

Temperature beyond which a liquid cannot exist; forms a supercritical fluid.

How does increased pressure affect phase?

Higher pressure favors solids and liquids (particles closer).

How does decreased pressure affect phase?

Favors gases (particles farther apart).

What is evaporation?

Surface-level liquid to gas below boiling point; endothermic.

How is evaporation different from boiling?

Evaporation occurs only at surface; boiling occurs throughout the liquid.

What increases evaporation rate?

Higher temperature, larger surface area, lower atmospheric pressure.

What decreases evaporation rate?

Lower temperature, high atmospheric pressure, small surface area.

Why does heat energy increase evaporation?

Faster-moving molecules escape the surface more easily.

How does atmospheric pressure affect evaporation?

Higher pressure slows evaporation; lower pressure speeds it up.

What is condensation?

Gas to liquid due to cooling or pressure increase; requires intermolecular forces to pull molecules together.

What are intermolecular cohesive forces?

Forces that pull molecules together; stronger forces make condensation easier.

What is the hydrologic cycle?

Movement of water through evaporation, condensation, and precipitation on Earth.

Role of evaporation in hydrologic cycle.

Water absorbs heat, becomes vapor, rises into atmosphere.

Role of condensation in hydrologic cycle.

Water vapor cools, condenses into liquid droplets forming clouds.

What is precipitation?

Liquid water falling from clouds as rain (or snow/sleet).

Why does warm air rise in the hydrologic cycle?

Convection currents push warm air upward, causing cooling and condensation.

What causes frost (deposition)?

Water vapor turns directly into ice when air is very cold.

Why do gases expand to fill a container?

Particles move freely with minimal intermolecular attraction.

Why do liquids take shape of container?

Particles slide while staying close together.

Why do solids keep shape?

Strong intermolecular forces keep particles fixed in place.

What happens to density during phase changes?

Solids are most dense, liquids less dense, gases least dense (exception: ice < water).

What happens to particle spacing in melting?

Particles spread farther apart as bonds weaken.

What happens to particle spacing in freezing?

Particles become closer or arranged into a rigid structure.

What happens to particle motion in melting?

Motion increases.

What happens to particle motion in freezing?

Motion decreases.

Why do gases have high compressibility?

Large empty space between particles.

What does endothermic mean in TEAS terms?

Heat is absorbed; temperature increases the movement of particles.

What does exothermic mean in TEAS terms?

Heat is released; particles slow and move closer.

Which phase changes are endothermic?

Melting, vaporization, sublimation.

Which phase changes are exothermic?

Freezing, condensation, deposition.

What is the relationship between density and particle spacing?

Closer spacing = higher density; farther spacing = lower density.

Why does higher temperature lower density in liquids?

Particles move apart slightly as kinetic energy increases.

Why does a balloon shrink in cold air?

Gas particles slow down and move closer together (lower kinetic energy).

Why does a balloon expand in heat?

Gas particles move faster and spread out.

Why can gases be compressed but not solids?

Gases have space between particles; solids do not.

How does increasing temperature affect volume of gases?

Increases volume (gas expands).

How does increasing pressure affect gases?

Decreases volume (particles pushed closer).

What process forms clouds?

Condensation of water vapor in cooling air.

What is needed for condensation to occur?

Particles must lose heat and come closer due to intermolecular forces.

What is the role of the Sun in evaporation?

Provides heat energy that speeds molecular motion.

Why does water evaporate slower on humid days?

Air already contains many vapor molecules, slowing evaporation.

Why does evaporation cool surfaces?

High-energy molecules leave, lowering average kinetic energy.