Honors Chemistry: Phase Changes, Gas Laws, and Atmospheric Pressure

What is atmospheric pressure?

Atmospheric pressure is caused by the force (weight) of air due to gravity.

What is standard atmospheric pressure?

Standard atmospheric pressure is air pressure at sea level (1 atm, 760 mmHg, 101.3 kPa).

What is evaporation?

Evaporation is the transition of particles from liquid to gas at a temperature below the boiling point.

What is vapor?

Vapor is a gas.

What is vapor pressure?

Vapor pressure is the pressure exerted by gas particles above a liquid.

What is the boiling point of a substance?

The boiling point is when the vapor pressure equals the atmospheric pressure and bubbles form.

What is the normal boiling point?

The normal boiling point is the temperature a liquid will boil at when the pressure above the liquid is at 760 mmHg.

What is the melting point?

The melting point is the temperature a solid changes into a liquid.

What is the freezing point?

The freezing point is the temperature a liquid changes into a solid.

What does it mean if a solid has a crystal structure?

A crystal structure means that the particles are arranged in an orderly, repeating, 3-D pattern.

What is a unit cell?

A unit cell is the smallest group of particles within a crystal that retains the geometric shape.

What are allotropes?

Allotropes are 2 or more different molecular structures of the same element.

What is an amorphous solid?

An amorphous solid lacks an ordered internal structure (atoms are randomly arranged).

What are examples of amorphous solids?

Rubber, plastic, wax, and glass are all examples.

What are the three assumptions of the kinetic theory of gases?

1. Gas particles have negligible volume and are very far apart. 2. Gas particles are in constant, random motion. 3. Gas particles have elastic collisions (no attractive forces between them).

What are three ways that pressure of a gas can be increased?

1. More particles (higher density). 2. Higher temperature. 3. Decreased volume.

What is the relationship between kinetic energy and temperature?

Temperature is a measure of the average kinetic energy of the particles in a substance; they are directly proportional.

What happens to atmospheric pressure as you change elevation?

As you increase elevation, there is less air pressure due to there being less gases higher in the atmosphere.

How does evaporation differ from boiling?

During evaporation, the temperature of the liquid decreases and there are no bubbles; during boiling, the temperature remains constant and bubbles form.

How is vapor pressure affected by temperature?

As temperature increases, vapor pressure increases.

At what point does boiling occur?

Boiling occurs when vapor pressure equals atmospheric pressure.

What happens to the boiling point of a liquid as the elevation changes?

At sea level, the boiling point of water is 100 degrees Celsius; above sea level, it decreases; below sea level, it increases.

What are the similarities and differences among the relative properties of solids, liquids, and gases?

The particles in liquids and gases can move and change shape; gases can also change volume and are compressible. Gases are the least dense and have the most kinetic energy, while solids are the most dense and have the lowest kinetic energy.

What are the six phase changes?

1. Melting: Solid to liquid. 2. Freezing: Liquid to solid. 3. Vaporizing: Liquid to gas. 4. Condensing: Gas to liquid. 5. Sublimation: Solid to gas. 6. Deposition: Gas to solid.

What is a phase diagram?

A phase diagram shows the relationship between temperature and pressure and their effects on the phases of matter for a substance.

What is a critical point?

The critical point is where the liquid and gas phases are indistinguishable and appear as one phase.

What is a triple point?

The triple point is where the solid, liquid, and gas phases all exist at equilibrium.

What do the lines represent on a phase diagram?

The lines represent the points at which a phase change occurs (where two phases exist at the same time).

What is sublimation?

Sublimation is the transition from solid to gas (e.g., dry ice, freeze-drying).

What is deposition?

Deposition is the transition from gas to solid (e.g., frost forming).