Unit Question

How can the appearance of a substance change without it becoming a different substance?

Chapter 1

Question: What happened to the liquid in Titan’s lake?

Investigations Questions: 

• How does the appearance of a substance change when it changes phase? (1.2)

• What happens to the molecules of a substance when it changes phase? (1.3, 1.4, 1.5, 1.6)

Key Concepts:

• A solid holds its shape and does not take the shape of its container. (1.2)

• A gas has no visible shape and fills its container. (1.2)

• A liquid flows and can take the shape of its container. (1.2)

• A solid keeps its shape because its molecules only move in place, not around each other. (1.5)

• A liquid can flow because its molecules move around, not away from each other. (1.5)

• A gas does not have a visible shape because gas molecules can move away from each other. (1.5)

• A phase change is when the molecules that make up a substance experience a change to their freedom of movement. This phase change involves a macroscale change in appearance. (1.6)

• A change that can be observed at the macroscale can be explained by a change at the molecular scale, which cannot be observed with the naked eye. (1.6)

Chapter 2

Question: What could cause liquid methane to change phase?

Investigations Questions: 

• What can cause molecules’ freedom of movement to change? (2.1)

• Why can transferring energy into or out of a substance change molecules’ freedom of movement? (2.2)

Key Concepts:

• What can cause molecules’ freedom of movement to change? (2.1)

• Why can transferring energy into or out of a substance change molecules’ freedom of movement? (2.2)

Chapter 3

Question: Why didn’t the liquid methane change phase before 2007?

Investigations Questions: 

• Why does an energy transfer not always result in phase change? (3.1, 3.2)

• How does molecular attraction affect whether or not a phase change will occur? (3.2, 3.3)

Key Concepts:

• Whether or not a phase change occurs is determined by the interaction between the kinetic energy of the molecules and the attraction pulling the molecules together. (3.2)

• The molecular attraction of a substance never changes. (3.2)

• A phase change occurs when the kinetic energy increases enough to overcome the attraction between molecules. (3.3)

• A phase change occurs when the kinetic energy decreases enough so that the attraction between molecules pulls them together. (3.3)

• Different substances can have either weaker or stronger molecular attraction. (3.3)

Chapter 4: Science Seminar

Question: Why is the liquid oxygen machine producing less liquid oxygen than normal?