Unit 3: Phase Change and Thermodynamics

Four Common Phases

Solid, Liquid, Gas, Plasma

What does an object phase depend on?

Temperature and Pressure

Definition of Evaporation

Change of phase from a liquid to a gaseous phase when more energy is added to the substance.

Describe the evaporation process

1. Molecules in the liquid move randomly at various speeds, colliding

2. Some molecules in the liquid gain kinetic energy as the temperature increases

3. Some energetic molecules escape and become a gas

4. The average kinetic energy of the remaining molecules in the liquid decreases, resulting in cooler water

Example of evaporation?

Sweat

Sublimation

A change directly from the solid to the gaseous state without becoming liquid

Example of Sublimation?

Dry Ice

Condensation

The change of state from a gas to a liquid

What is condensation the opposite of?

evaporation

Describe the condensation process

1. Condensation is the opposite of evaporation.

2. Gas molecules near a liquid surface are attracted to the liquid and strike the liquid's

surface, becoming part of the liquid.

3. The kinetic energy of the striking molecules is absorbed by the liquid, resulting in

increased temperature.

If you accidentally grab a hot panhandle while cooking, it's best if your hand is:

Wet

Boiling

The change of phase from liquid to gas by rapid evaporation beneath the surface of a liquid.

Describe Boiling

-Rapid form of evaporation beneath the surface forms vapor bubbles.

- Bubbles rise to the surface.

-If vapor pressure in the bubble is less than the surrounding pressure, then the bubbles

collapse.

-At boiling point, when the vapor pressure in the bubble is sufficient, bubbles of gas

escape the liquid.

What does the process of boiling do?

Cools the water being boiled and is a change of phase below the water surface.

Melting

The change in state from a solid to a liquid

Describe Melting

1. When heat is supplied to a solid, the molecular bonds that form the structure of the solid

vibrate more.

2. If the vibration is strong enough, the molecular bonds break and the molecules come

loose from the structure.

3. The breakdown of the molecular structure of the solid make the substance change into a

liquid.

Freezing

The change of state from a liquid to a solid

Describe Freezing

-Opposite of melting

-As energy is continually removed from a liquid, its molecular motion decreases

- When molecules move about less, chemical forces of attraction bind them together

- The bonds hold the molecules in their structure, turning the substance into a solid

When the direction of phase is solid - liquid - gas - plasma, then the substance

_______________ in energy.

Increases

When the direction of phase is plasma -gas - liquid - solid, then the substance

_______________ in energy.

Decreases

The internal energy of a substance changes during phase change but the temperature of the substance___________________________________________________________.

Does not change

When snow forms in clouds, the surrounding air is

warmed

Thermodynamics

The study of the relationship between heat, temperature, energy, and work

First Law of Thermodynamics/Law of Conservation of Energy

Energy can neither be created nor destroyed. It can only be converted from one form to another.

What is the equation for the law of conservation of energy?

ΔE= Q-W

Heat Engine

A closed system that converts heat into mechanical work

What two things does every heat engine have?

A reservoir of heat at a high temperature and a sink at a lower temperature

Adiabatic Process

The expansion or contraction of a gas with no change in temperature

What's the equation of an adiabatic process?

ΔE = -W

Second Law of Thermodynamics

The entropy of an insulated system tends to increase.

Entropy

The amount of internal energy that is not available to do work. (Wasted Energy)

Ideal Efficiency Equation

Tʰ - Tᶜ/ Tʰ x 100