Phases
This phase has a definite shape because its molecules only move in place.
This is the process of a solid changing into a liquid.
What is melting?
a group of atoms joined together in a particular way
molecule
If I add the same amount of energy into two substances that are solids and only one turns into a liquid, which substance has the weaker molecular attraction?
The substance that changes phase
This is a measure of the average kinetic energy of the molecules in a substance.
What is temperature?
This phase can flow because its molecules move around each other.
What is a liquid?
This is the process of a liquid changing into a gas.
What is evaporation?
a measure of how hot or cold something is
temperature
If I take out the same amount of energy from two substances that are gases and only one turns into a liquid, which substance has the weaker molecular attraction?
The substance that did not change phase.
This is the pull between molecules that is always the same for a particular substance.
What is molecular attraction?
In this phase, molecules can move away from each other, so the substance does not have a visible shape.
What is a gas?
What happens to the average kinetic energy of molecules when energy is added to a substance?
It increases.
the way molecules in a substance move around relative to each other
freedom of movement
If I take out the same amount of energy from two substances that are liquids and only one turns into a solid, which substance has the stronger molecular attraction?
The substance that changed phase
When energy is transferred away from a substance, what happens to the molecules' kinetic energy?
It decreases.
A substance has molecules that are close together but can move around each other. What phase is it in, and what does this tell you about its molecules' freedom of movement?
What is a liquid? Its molecules have more freedom of movement than molecules in a solid.
A solid is heated until it becomes a liquid. Explain what happens to its kinetic energy and freedom of movement.
Kinetic energy increases, causing the molecules to have more freedom of movement.
a pull between two molecules that is always the same for a substance
molecular attraction
If I add the same amount of energy to two substances that are liquids and only one turns into a gas, which substance has the stronger molecular attraction?
The substance that did not change phase
Two substances are heated. Substance A changes phase before Substance B. What could you infer about their molecular attractions?
Substance A may have weaker molecular attraction than Substance B.
A student says, “Gas molecules are bigger than solid molecules.” Use what you know about molecular movement to refute this claim.
Gas molecules are not necessarily bigger. The molecules have more freedom of movement and can move farther apart from one another.
A student says, “A phase change happens because the molecules become a completely different substance.” Use molecule, kinetic energy, and phase change to refute the claim.
The molecules do not become a different substance. Their kinetic energy and freedom of movement change, causing the substance to change phase.
the energy that an object has because it is moving
Why did the lake on Titan not change phase from 2002-2007 even though energy was being added to it?
The kinetic energy was not able to overcome the molecular attraction between the methane molecules
Explain why adding energy can cause a solid to become a liquid. Use temperature, kinetic energy, molecular attraction, and freedom of movement.
Adding energy increases temperature and kinetic energy. When the molecules have enough kinetic energy to overcome some of the molecular attraction, they can move around each other, increasing their freedom of movement and causing a phase change.