MS – PS 1.4

Chapter 2 Pearson

Energy – the ability to do work or cause change

LCD in a TV or cell phone stands for Liquid Crystal Display. They use less power. Liquid Crystal is neither solid nor liquid – they are somewhere in between. It takes just a small amount of thermal energy to change a liquid crystal to a liquid, so LCDs are very sensitive to heat.

Solid – has a definite shape and volume.

The particles that make up a solid are packed very closely together and are tightly fixed in one position. The particles can move, but are so closely locked in position, that they can only vibrate in place. (like a group of people running in place)

Types of solids –

Solids made up of particles that form a regular, repeating pattern are

called crystalline solids. Salt, sugar, and snow are examples of crystalline solids. When a crystalline solid is heated, it will melt at a certain temperature.

Snowflake being formed:

https://www.youtube.com/watch?v=MCA2VmDVzEo

Amorphous solids have particles NOT arranged in a regular pattern, and they do not melt at a distinct temperature. Instead, it will just

become softer or change into another substance.

Glass, plastics, and rubber are examples of amorphous solids.Glass blowing video:

https://www.youtube.com/watch?v=dtxrtKd-Vao

Describing a liquid –

Liquid – has a definite volume, but no shape of its own

The particles in a liquid are packed almost as closely together as in a solid, but they can move around one another freely

These freely moving particles allow a liquid to flow from place to place. A liquid is also called a fluid, meaning “a substance that flows.”

Properties of a liquid –

Surface Tension – the inward pull among the molecules in a liquid that brings the molecules on the surface closer together

Viscosity – a liquid’s resistance to flowing

Water has a low viscosity; honey has a high viscosity

Describing a Gas –

Like a liquid, gas is also considered a fluid, but gas does NOT have a definite shape nor a definite volume.

Gas particles will move and spread about in a container.

Volume – the amount of space that matter fills. Volume can be measured in cubic centimeters (cm³) cubic meters (m³), milliliters (mL), liters (L). Gas particles move and fill all of the space available, so a volume of gas is the same as the volume of the container.

Gas particles are constantly colliding with one another and with the walls of their container.

Pressure – the force of the outward push divided by the area of the walls of the container

Example – the air inside an inflated ball has a higher pressure than the air outside, because there is a higher concentration of gas particles inside the ball than in the surrounding air.

The firmness of a gas-filled object comes from the pressure of the gas. When a ball has a tiny hole, air leaks out because the gas particles inside the ball reach the hole and escape more often than gas particles outside the ball are going in. The pressure inside drops until it is equal to the pressure outside.

Temperature - is a measure of the average energy of random motion of particles of matter.

The faster the particles are moving, the greater their energy and the higher the temperature. (So a thermometer is really like a speedometer for particles in a liquid)

Even at room temperature, the average speed of particles in a gas is very fast. At 20*C, the particles are traveling about 500 meters per

second – that’s twice the speed of a jet plane.

In a hot air balloon, a propane burner is used to heat the air inside the balloon. Once the temperature of the air is hot enough, the balloon will begin to rise.https://www.youtube.com/watch?v=46Tgd5WJUUg

hot air balloon taking off

CHANGES of STATE of MATTER

What happens to the Particles of a Solid as It Melts?

Particles of a liquid have more thermal energy than the same

substance in solid form. A change from a solid to a liquid involves an increase in thermal energy . A change from a liquid to a solid involves a DECREASE in thermal energy.

The change in state from a solid to a liquid is called melting. In crystalline solids, melting occurs at a specific temperature called the melting point. Chemists compare melting points when trying to identify an unknown material. The melting point of pure water is 0*C.

The energy needed to melt an ice cube comes mostly from the air in the room. The added thermal energy makes the water molecules vibrate faster, raising their temperature. At a solid’s melting point, its particles vibrate so fast that they break free from their fixed positions. At 0*C, the temperature of ice stops increasing. Any added energy continues to change the arrangement of the water molecules from ice crystals into liquid water, and the ice melts.

Freezing: The change of state from a liquid to a solid is called freezing. At a liquid’s freezing point, its particles are moving so slowly that they begin to take on a fixed position. When water is put in a

freezer, the water loses energy to the cold air in the freezer. The water molecules move more and more slowly as they lose energy, then become solid ice.

What happens to the Particles of a Liquid as it Vaporizes?

The change in state from a liquid to a gas is called vaporization. Vaporization occurs when the particles in a liquid gain enough energy to move independently.

Two types of vaporization:

Evaporation – vaporization that takes place only on the surface of a liquid (like a shrinking puddle). Water in the puddle gains energy from the ground, the air, or the sun. The added energy helps some of the water molecules escape into the air.

Boiling: vaporization that takes place both below and at the surface of a liquid. When water boils, vaporized water molecules form bubbles below the surface. The

bubbles rise and break the surface of the liquid. The temperature at which a liquid boils is called its boiling point.

Condensation: Change in state from a gas to a liquid (reverse of vaporization) Example: when breathing on a mirror, the warm water vapor in your breath reaches the cooler surface of the mirror, and the water vapor condenses into liquid droplets. Condensation occurs when particles in a gas lose

enough thermal energy to form a liquid.

Clouds typically form when water vapor in the atmosphere condenses into tiny liquid droplets. When the water droplets get heavy enough, they fall as rain. Water vapor is a gas – steam, clouds, and fog are not – they are water droplets.

What Happens to the Particles of a Solid as it Sublimes?

Sublimation occurs when the surface particles of a solid gain enough energy that they form a gas.

Vapor is another word for gas

Dry Ice

Dry ice is solid carbon dioxide. At ordinary atmospheric pressure, carbon dioxide cannot exist as a liquid. So instead of melting, it changes directly into a gas. When dry ice becomes a gas, it cools water

vapor in the nearby air. The water vapor then condenses into a liquid, forming fog near the dry ice.