Particle Model of Matter
What's covered
Key facts
Density
A 240 g block with a volume of 30 cm³ has a density of 8 g/cm³.
Gas Laws
At absolute zero, gas particles theoretically have no kinetic energy.
Gas Pressure
Gas exerts pressure on container walls because particles collide with the walls, each exerting a force per collision.
Internal Energy
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
Latent heat is the energy needed to change state without a change in temperature.
States of Matter
Deposition is the change of state in which a gas turns directly into a solid (without passing through the liquid state).
Temperature and Thermal Energy
100 °C = 100 + 273 = 373 K.
Density
A 540 g block with volume 200 cm³ has a density of 540 ÷ 200 = 2.7 g/cm³.
Gas Laws
A 2 m³ gas at 100 kPa compressed to 0.5 m³ at constant T gives p₂ = p₁V₁/V₂ = 100 × 2 / 0.5 = 400 kPa.
Gas Pressure
Compressing a gas increases pressure because particles experience more collisions per area per second.
Sample questions
A taste of the 66 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
If gas volume halves at constant temperature, pressure:
- ✓Doubles
- •Halves
- •Quadruples
- •Unchanged
What happens to gas pressure if temperature increases at fixed volume?
- •Pressure becomes zero
- •Pressure decreases
- ✓Pressure increases
- •Pressure stays the same
What happens to internal energy during a change of state at constant temperature?
- •Both kinetic and potential energy decrease
- •Internal energy stays completely constant throughout
- •Kinetic energy increases while potential energy falls
- ✓Potential energy increases while kinetic energy stays the same
What is latent heat?
- •Energy needed to raise temperature only
- ✓Energy to change state without temperature change
- •Heat lost when particles condense downward
- •Heat used to break chemical bonds apart
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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