Mastering Phase Changes in Matter

Professor Dave explains phase changes, including melting, freezing, sublimation, and deposition. He discusses vapor pressure, boiling points, and how these are affected by atmospheric pressure. The video covers the concepts of freezing and melting points, heat of fusion and vaporization, and phase diagrams, including the triple point. The video concludes with a comprehension check.

What is the process called when a solid turns directly into a gas?

• Melting

• Deposition

• Sublimation

• Condensation

Which of the following processes involves a change in enthalpy?

• Freezing

• Melting

• All of the above

• Boiling

What happens to the boiling point of water as atmospheric pressure decreases?

• It increases

• It decreases

• It remains the same

• It fluctuates

At what temperature does a liquid turn into a crystalline solid?

• Boiling point

• Melting point

• Freezing point

• Sublimation point

During which phase change does the temperature of a substance remain constant?

• Melting

• Boiling

• Both melting and boiling

• Neither melting nor boiling

What is the energy required to change a solid to a liquid called?

• Heat of fusion

• Hydrogen bond energy

• Lattice energy

• Heat of vaporization

What does a phase diagram illustrate?

• The pressure of a substance

• The temperature of a substance

• The phase of a substance at various temperatures and pressures

• The density of a substance

What is the triple point on a phase diagram?

• The point where all three phases coexist in equilibrium

• The point where a substance is only a gas

• The point where a substance is only a liquid

• The point where a substance is only a solid

Why does the line between solid and liquid slant up and left for water on a phase diagram?

• Because water cannot sublimate

• Because water is always a liquid at atmospheric pressure

• Because the liquid form is denser than the solid form

• Because the solid form is denser than the liquid form

Why does dry ice typically sublimate at atmospheric pressure?

• Because carbon dioxide is denser as a gas

• Because carbon dioxide is never a liquid at atmospheric pressure

• Because carbon dioxide has a high boiling point

• Because carbon dioxide is always a liquid at atmospheric pressure