Question 1

Which of the following best describes what happens to the temperature of ice as it melts in a well-insulated container at 0°C?

Accepted Answer

The temperature remains constant at 0°C until all the ice has melted.

Question 2

At standard atmospheric pressure, what is the boiling point of water, and why does it change in a pressure cooker?

Accepted Answer

100°C; because the pressure is higher inside a pressure cooker, raising the boiling point.

Question 3

Which phase change occurs when dry ice (solid CO₂) is left at room temperature and atmospheric pressure?

Accepted Answer

Sublimation

Question 4

What is the significance of the triple point of water?

Accepted Answer

It is the only temperature and pressure where solid, liquid, and gas phases of water coexist in equilibrium.

Question 5

Why does ice float on liquid water?

Accepted Answer

Because ice is less dense than liquid water.

Question 6

Which of the following statements about the critical point on a phase diagram is correct?

Accepted Answer

Above the critical point, liquid and gas phases are indistinguishable.

Question 7

If you compress ice at 0°C, what unusual property of water might you observe?

Accepted Answer

The ice will turn into liquid water due to increased pressure.

Question 8

What is the Kelvin temperature corresponding to the triple point of water?

Accepted Answer

$$273.16\ \mathrm{K}$$

Question 9

Which process describes the direct transition from gas to solid?

Accepted Answer

Deposition

Question 10

A CO₂ fire extinguisher contains liquid carbon dioxide. What does this imply about the pressure inside the extinguisher?

Accepted Answer

The pressure is greater than 5 atm.

Question 11

Why is the triple point of water used as a reference for the Kelvin temperature scale?

Accepted Answer

Because it is independent of pressure and allows for a unique reference.

Question 12

Which of the following best describes phase equilibrium?

Accepted Answer

A state where two or more phases coexist at specific temperature and pressure.

Question 13

At what temperature and pressure does the triple point of water occur?

Accepted Answer

$$0.01\ ^\circ\mathrm{C}$$ and $$0.006\ \mathrm{atm}$$

Question 14

Which of the following statements about the melting and freezing points of water is correct?

Accepted Answer

The melting and freezing points are the same at a given pressure.

Question 15

Why does food cook faster in a pressure cooker?

Accepted Answer

Because the boiling point of water is raised, so food cooks at a higher temperature.

Question 16

Which of the following is true about the phase diagram of water?

Accepted Answer

The solid-liquid boundary slopes to the left due to ice being less dense than liquid water.

Question 17

Steam can be heated above 100°C in a sealed container. What does this demonstrate about the properties of gases?

Accepted Answer

The boiling point of a liquid depends on the external pressure.

Question 18

Which of the following best explains why the Celsius scale is not ideal for defining temperature standards?

Accepted Answer

Because the reference points (melting and boiling points of water) vary with pressure.

Question 19

What happens to the temperature of water as it boils at 1 atm pressure?

Accepted Answer

It remains constant at 100°C until all the water has boiled.

Question 20

Which of the following is the correct value for absolute zero on the Celsius scale, as used in calculations with significant figures?

Accepted Answer

$$-273\ ^\circ\mathrm{C}$$

Phase Changes and Phase Diagrams in Properties of Matter

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