PS1-3 Phase Changes Review

Exam Review

PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.

Draw

Sketch a heating curve for water (Don't worry about exact numbers)

Multiple Choice

If we continuously heat a liquid, what happens to the temperature of when it starts to boil (during a phase change)?

• The temperature stays the same

• The temperature increases

• The temperature decreases

Multiple Choice

What is the approximate boiling point of this liquid?

• 0 °C

• 1500 °C

• 2700 °C

• 4000 °C

Open Ended

Why does the heating curve of water have this shape? Talk about when it is increasing and when it is flat. Use CER for full marks. Include words like particles, forces, energy and temperature.

Why does the heating curve of water have this shape? Talk about when it is increasing and when it is flat. Use CER for full marks. Include words like particles, forces, energy and temperature.

C: Heating curves have this shape because as heat is added, the substance goes through phase changes.

E: The graph is flat at 0°C and 100°C. When the substance is not at these temperatures, the graph rises at a constant rate.

R: As heat is added, the heat is used to increase the temperature of the water. When the water undergoes a phase change, the energy is used to break the bonds between water particles, so the temperature remains constant. The breaking of bonds weakens the forces between particles, causing the water to change states.

Multiple Choice

Substance A has a boiling point of 70°C and substance B has a boiling point of 120°C. Which substance has stronger forces between particles?

• Substance A

• Substance B

Open Ended

Why does a substance with a higher boiling point have stronger forces between particles? Use CER for full marks.

Why does a substance with a higher boiling point have stronger forces between particles? Use CER for full marks.

C: A substance with a higher boiling point has stronger forces between particles because it takes more energy to overcome the forces.

E: In two different heating curves, the one with a higher boiling point needs more heat (energy) added to undergo a phase change.

R: More heat (energy) is required to break the bonds between particles for a substance with a higher boiling point.

Draw

Label 0°C and 100°C. Mark the letter A where water goes from solid to liquid and a B where water goes from liquid to gas.

Audio Response

What state do you think substance A is in? Justify your answer.

Open Audio Recorder

What state do you think substance A is in? Justify your answer.

1. It is a liquid, and the temperature is increasing until it reaches the boiling point.

2. It is a gas, and the temperature will continue to increase.

(It cannot be a solid because it has already gone through one state change)

Open Ended

Use your answer from the last question, to compare the forces between particles of substance A and water. Use CER for full marks.

Use your answer from the last question, to compare the forces between particles of substance A and water. Use CER for full marks.

Using substance A as a liquid.

C: Substance A has stronger forces between particles.

E: According to the graph, Substance A has undergone one state change, and water has had two state changes.

R: Substance A has only had one state change, so it is in liquid form and has a higher boiling point than water. Water has had two state changes and is a gas. Substances with higher boiling points have stronger forces between particles because it takes more energy to overcome the forces.

Match

Match the following:

• Melting point

• Boiling point

• Particle

• Heat

• Temperature

Temperature at which a solid becomes a liquid

Temperature at which a liquid becomes a gas

A small portion of matter

Energy that is transferred from one thing to another

The measure of hotness of coldness

• Temperature at which a solid becomes a liquid

• Temperature at which a liquid becomes a gas

• A small portion of matter

• Energy that is transferred from one thing to another

• The measure of hotness of coldness

Draw

This is a sample of solid Nitrogen that is melted by continuous heating. Label where it is a solid, liquid and the phase change.

Open Ended

The temperature increases quickly, then slows down and increases quick again. Why? Use kinetic energy, force and bond in your answer.

The temperature increases quickly, then slows down and increases quick again. Why? Use Kinetic Energy, Force and Bond in your answer.

At first, Nitrogen is in solid state and the heat energy added will increase the kinetic energy (increasing the temperature)

Between about 200 - 1200 minutes, the temperature increases slowly because the nitrogen is in a state change. The energy increase is being used to weaken the forces between particles and break the bonds.

When Nitrogen becomes all liquid, the temperature begins to increase again as the kinetic energy of the particles increases.

Audio Response

What do you observe in the graph?

Open Audio Recorder

What do you obeserve in the graph?

When heat is supplied, the temperature goes up. When the graph is transitioning from solid to liquid or liquid to gas (undergoing a phase change) the temperature remains the same, even though more heat is being supplied.

Open Ended

Use CER to answer, "What does the graph show?"

Use CER to answer, "What does the graph show?"

C: The graph shows the heating curve if a substance.

E: It shows three different states of matter, solid, liquid, and gas. It shows that as heat is supplied, temperature increases, unless there is a state change.

R: As heat is added to a solid, the temperature increases until the melting point. At the melting point, the temperature remains constant as we add heat as the energy is being used to break the bonds. Once melted, adding heat increases temperature again until we reach the boiling point. When the substance changes from liquid to gas, the temperature remains constant because the heat is being used to break the bonds between particles.

Multiple Choice

The boiling point of CH₃Cl is -24.2°C. The boiling point of CH₃F is -78.6°C. Which has the strongest intermolecular forces?

• CH₃Cl

• CH₃F

Why does a substance with a higher boiling point have stronger forces between particles? Use CER for full marks.

C: A substance with a higher boiling point has stronger forces between particles because it takes more energy to overcome the forces.

E: In two different heating curves, the one with a higher boiling point needs more heat (energy) added to undergo a phase change.

R: More heat (energy) is required to break the bonds between particles for a substance with a higher boiling point.

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