Flashcards · 8463 · Topic 3

Particle model of matter flashcards

19 cards on Topic 3, subtopics 4.3.1 to 4.3.3. Pick a subtopic or study them all.

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Density equation, with units: ρ = m / V ρ in kg/m³, m in kg, V in m³.
Why is a gas much less dense than the same substance as a solid or liquid?: The same mass of particles is spread over a much bigger volume, because gas particles are far apart.
Particle arrangement and motion in a solid, a liquid and a gas: Solid: touching, regular, vibrate in place. Liquid: touching, irregular, slide past each other. Gas: far apart, random, move fast in all directions.
Why is a change of state a physical change?: Mass is conserved and, if the change is reversed, the material gets its original properties back. No new substance forms.
Required practical 5: finding the volume of an irregular solid: By displacement: measure the rise in water level in a measuring cylinder, or collect the overflow from a eureka can in a measuring cylinder.
A 0.60 kg block has a volume of 2.4 × 10⁻⁴ m³. What is its density?: ρ = 0.60 ÷ 2.4 × 10⁻⁴ = 2500 kg/m³
Sublimation: A change of state from solid straight to gas.

Internal energy: The total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system.
Two things heating a system can do: Raise its temperature (particles gain kinetic energy), or change its state (particles gain potential energy, temperature stays constant).
Specific latent heat: The energy needed to change the state of 1 kg of a substance with no change in temperature. E = mL (J, kg, J/kg).
Specific latent heat of fusion vs of vaporisation: Fusion: solid ↔ liquid. Vaporisation: liquid ↔ vapour.
What is happening on a flat section of a heating graph?: A change of state (melting or boiling). The energy supplied raises the internal energy, but the temperature stays constant. Use E = mL, not ΔE = mcΔθ.
How much energy melts 0.50 kg of ice at 0 °C? (L = 334 000 J/kg): E = mL = 0.50 × 334 000 = 167 000 J

What causes gas pressure?: Molecules in constant random motion collide with the container walls, producing a net force at right angles to the wall.
Temperature of a gas is related to…: The average kinetic energy of its molecules.
Why does the pressure of a gas rise when it is heated at constant volume?: The molecules move faster, so they hit the walls more often and with more force.
Why does the pressure of a gas fall when its volume increases at constant temperature?: The molecules move at the same speed but hit each unit area of the wall less often.
Gas at 200 kPa in 0.050 m³ is compressed to 0.020 m³ at constant temperature. New pressure?: p₁V₁ = p₂V₂, so p₂ = 200 × 0.050 ÷ 0.020 = 500 kPa
Why does a bicycle pump get warm when you use it?Higher: Work is done on the gas (work is the transfer of energy by a force). This increases the internal energy of the gas, so its temperature rises.