Chemistry: States of Matter and Particle Models
Explaining solids, liquids, gases, and changes of state with particles
Chemistry: States of Matter and Particle Models
Explaining solids, liquids, gases, and changes of state with particles
Chemistry - Grade 6-8
- 1
A student draws particles in a solid as tightly packed circles in a fixed pattern. Explain what the particles are doing even though the solid keeps its shape.
Think about motion that happens without changing position very much.
The particles in a solid vibrate in place. They do not move freely past one another, so the solid keeps a definite shape and volume. - 2
Compare the particle spacing and particle motion in a liquid and a gas.
In a liquid, particles are close together but can slide past one another. In a gas, particles are far apart and move quickly in many directions. - 3
A sealed balloon is placed in a warm room, and the balloon gets slightly larger. Use the particle model to explain why this happens.
Temperature is related to the average kinetic energy of particles.
The gas particles gain kinetic energy in the warmer room. They move faster, hit the inside of the balloon more often and harder, and cause the balloon to expand. - 4
Classify each substance as a solid, liquid, or gas at room temperature: ice cube, helium in a party balloon, cooking oil, and a metal spoon.
An ice cube is a solid, helium in a party balloon is a gas, cooking oil is a liquid, and a metal spoon is a solid. - 5
A beaker of water is heated on a hot plate. Describe what happens to the water particles as the temperature rises before boiling begins.
Focus on particle motion before the liquid changes into a gas.
As the temperature rises, the water particles gain kinetic energy and move faster. They remain close together as a liquid until enough energy is added for boiling to begin. - 6
Name the change of state when water vapor cools and forms liquid droplets on the outside of a cold glass. Explain the particle change.
The change of state is condensation. Gas particles lose energy, slow down, move closer together, and become liquid droplets. - 7
During melting, does the temperature of a pure substance usually keep rising, or does it stay nearly constant until melting is complete? Explain why.
Think about where the added heat energy goes during a phase change.
During melting, the temperature of a pure substance usually stays nearly constant until melting is complete. The added energy is used to loosen particle attractions instead of increasing average kinetic energy. - 8
A student says, "When a puddle evaporates, the water disappears and no longer exists." Correct this statement using the particle model.
Matter is still present even when it is too spread out to see.
The water does not disappear. During evaporation, some liquid water particles gain enough energy to escape into the air as water vapor. - 9
Look at a particle diagram showing particles packed close together but arranged randomly and able to slide. Which state of matter does the diagram represent? Explain your answer.
The diagram represents a liquid. The particles are close together like a condensed state, but their random arrangement and ability to slide show that the substance can flow. - 10
Dry ice is solid carbon dioxide. At room temperature, it changes directly from a solid to a gas without becoming a liquid. Name this change of state and describe the particle energy change.
This change skips the liquid state.
This change of state is sublimation. The particles gain enough energy to move from a tightly packed solid arrangement directly into the widely spaced motion of a gas. - 11
A gas is compressed in a syringe by pushing the plunger down while the tip is sealed. What happens to the spacing between gas particles and the volume of the gas?
The spacing between gas particles decreases, and the volume of the gas decreases. The number of particles stays the same, but they are forced into a smaller space. - 12
Explain why a liquid takes the shape of its container but a solid usually does not.
Compare how freely the particles can move in each state.
A liquid takes the shape of its container because its particles can move and slide past one another. A solid usually does not because its particles are held in fixed positions and only vibrate.