Solids, Liquids, and Gas

Changes of State

Changes in State

1. Changes Between Solid and Liquid

A. Melting

  • Melting is the change in state from solid to liquid, involving an increase in thermal energy.

  • Pure substances have a specific melting temperature known as the melting point, for example, 0°C for water.

  • Increased thermal energy causes solid particles to vibrate, leading to melting.

2. Changes Between Liquid and Gas When a liquid is heated to its boiling point, it undergoes a phase transition known as vaporization, where the molecules gain enough energy to break free from the liquid state and enter the gas phase.

3. Changes Between Liquid and Gas

Vaporization

  • Vaporization is the change from liquid to gas, which occurs when particles gain sufficient energy.

  • Types of Vaporization:

    1. Evaporation: Takes place on the surface of a liquid.

    2. Boiling: Occurs both on the surface and below, creating bubbles.

Boiling Point

  • The boiling point is the temperature at which vaporization occurs and varies with air pressure.

  • Example: Water boils at 100°C at sea level but lower at higher elevations (e.g., 95°C in Denver).

4. Condensation

  • Condensation is the opposite of vaporization, where gas particles lose thermal energy to form a liquid, as seen when breathing on a cool surface.

5. Changes Between Solid and Gas

Sublimation

  • Sublimation occurs when solid particles gain energy to form a gas without passing through the liquid state.

  • Example: Dry ice (solid CO2) sublimates directly into gas without becoming a liquid, absorbing thermal energy, which leads to fog formation when water vapor condenses.

Section 2 Assessment

Reviewing Key Concepts

  1. a. As a solid becomes a liquid, its particles gain thermal energy and vibrate faster.b. The thermal energy of solid water increases as it melts.c. Melting snow is preferable to eating it, as the former provides liquid water for hydration.

  2. a. Vaporization is the transition from liquid to gas.b. The two types of vaporization are evaporation and boiling; they differ in their mechanism and location of the process but both yield gas from liquid.c. Sweat evaporation cools the body as heat from the skin is used to change sweat (liquid) into vapor.

  3. a. Dry ice sublimates as it gains energy to form gas directly.b. The fog around dry ice is caused by water vapor condensing into tiny droplets due to cold temperatures.

Writing in Science

  • Using Analogies: Write about particle motion, comparing it to people dancing, illustrating the different motions and positions in liquid water and water vapor.