Question

1. start with the substance as a solid.

○ what do the particles look like?
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○ what happens when you slowly increase the temperature?
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○ at what point do you notice a change of state? (describe)
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1. now change the substance to liquid and begin at a moderate temperature.

○ describe the movement of particles in the liquid state.
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○ what happens when you increase the temperature further?
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○ what happens when you decrease the temperature?
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1. finally, start with the substance as a gas.

○ describe how the particles behave in the gas state.
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○ what happens when you decrease the temperature slowly?
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○ at what moment do you see condensation or change to a liquid?
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Explanation:

1.

• Particles in solid: In a solid, particles are closely packed in a regular, fixed pattern. They vibrate in place but do not move freely.
• Effect of heating solid: When the temperature of a solid is slowly increased, the particles gain kinetic energy. Their vibrations become more vigorous.
• Change of state in solid: A change of state (melting) is noticed when the temperature reaches the melting point. At this point, the solid starts to turn into a liquid as the forces holding the particles in the fixed pattern are overcome.

2.

• Particle movement in liquid: In the liquid state, particles are still close together but have more freedom of movement than in a solid. They can slide past one another.
• Effect of further heating liquid: When the temperature of a liquid is increased further, the particles gain more kinetic energy. Evaporation (and eventually boiling if the temperature is high enough) occurs as particles escape from the liquid surface (or throughout the liquid in boiling).
• Effect of cooling liquid: When the temperature of a liquid is decreased, the particles lose kinetic energy. The liquid may eventually solidify (freeze) if the temperature is low enough (reaching the freezing point).

3.

• Particle behavior in gas: In the gas state, particles are far apart and move freely in all directions at high speeds. They have a lot of kinetic energy.
• Effect of cooling gas: When the temperature of a gas is slowly decreased, the particles lose kinetic energy. Their movement slows down.
• Condensation in gas: Condensation (change to a liquid) is seen when the temperature reaches the condensation point. At this moment, the particles have lost enough kinetic energy that the attractive forces between them become significant enough to pull them closer together and form a liquid.

Answer:

1.

• Particles in solid: Closely - packed, vibrating in fixed positions.
• Effect of heating solid: Particles vibrate more vigorously.
• Change of state in solid: At melting point, solid turns to liquid.

2.

• Particle movement in liquid: Can slide past each other.
• Effect of further heating liquid: Evaporation (or boiling) occurs.
• Effect of cooling liquid: May solidify (freeze).

3.

• Particle behavior in gas: Move freely, far apart.
• Effect of cooling gas: Particles slow down.
• Condensation in gas: At condensation point, gas turns to liquid.