Particle Model of Matter
What's covered
Key facts
A 240 g block with a volume of 30 cm³ has a density of 8 g/cm³.
Absolute zero (0 K) corresponds to −273 °C (more precisely −273.15 °C).
Gas exerts pressure on container walls because particles collide with the walls, each exerting a force per collision.
Heating a substance can either raise its temperature (between state changes) or change its state (during a state change), depending on whether particles are absorbing kinetic or potential energy.
Latent heat is the energy needed to change state without a change in temperature.
Deposition is the change of state in which a gas turns directly into a solid (without passing through the liquid state).
100 °C = 100 + 273 = 373 K.
A 540 g block with volume 200 cm³ has a density of 540 ÷ 200 = 2.7 g/cm³.
At absolute zero, gas particles theoretically have no kinetic energy.
Compressing a gas increases pressure because particles experience more collisions per area per second.
Sample questions
A taste of the 81 questions in this topic — answers marked. Sign up to practise the full set with spaced repetition.
Which equation correctly defines density?
- •ρ = m × V; units kg·m³
- ✓ρ = m/V; units kg/m³ or g/cm³
- •ρ = m/V²; units kg/m⁶
- •ρ = V/m; units m³/kg
Why does pressure rise when a gas is heated at constant volume?
- ✓Faster particles collide harder and more often with walls
- •Gas molecules attract one another more
- •More particles appear inside the container
- •The container becomes smaller as it heats
What causes gas pressure?
- •Gravity pulling gas downward
- •Heat radiating from container
- •Particles attracting each other
- ✓Particles colliding with container walls
What is internal energy?
- •Energy lost to surroundings while warming
- •Only kinetic energy stored by particles
- •Only potential energy stored by particles
- ✓Total kinetic and potential energy of particles
Why does temperature stay constant during a change of state even though energy is supplied?
- ✓Energy breaks intermolecular bonds rather than increasing particle kinetic energy
- •Energy is lost completely to the surroundings as heat during the change of state
- •Energy is stored in atomic nuclei during the transition and released later
- •Temperature cannot be measured accurately while a substance is changing state
How are particles arranged differently in a solid compared with a gas?
- •Both close-packed, but gas particles vibrate more energetically in place
- •Solid particles have far more kinetic energy than gas particles do
- ✓Solid: close-packed in fixed positions; gas: spread apart, moving randomly
- •Solid: spread far apart, moving randomly; gas: close-packed in fixed positions
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