Flashcards · 4PH1 · Topic 5

Solids, liquids and gases flashcards

21 cards on Topic 5, subtopics 5a to 5d. Pick a subtopic or study them all.

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Units of density and of pressure: Density: kilogram/metre³ (kg/m³). Pressure: pascal (Pa); 1 Pa = 1 N/m².
Units of temperature: Degree Celsius (°C) and kelvin (K). A change of 1 K equals a change of 1 °C.
Unit of specific heat capacity: Joules per kilogram degree Celsius (J/kg °C). (Paper 2 only)

Density equation: Density = mass ÷ volume, ρ = m/V.
How do you find the density of an irregular solid?: Measure its mass on a balance. Find its volume by displacement: the rise in water level in a measuring cylinder. ρ = m/V.
Pressure equation: Pressure = force ÷ area, p = F/A.
In which direction does pressure act in a liquid or gas at rest?: Equally in all directions at a given point.
Pressure difference between the surface and 5.0 m deep in water (ρ = 1000 kg/m³, g = 9.8 N/kg): p = h × ρ × g = 5.0 × 1000 × 9.8 = 49 000 Pa.
Why is a dam built thicker at the base?: Pressure in a liquid depends only on depth and density (not the container's shape or the volume), so it is greatest at the bottom.

Particle arrangement and motion in solids, liquids and gases: Solid: regular, close-packed, vibrate about fixed positions. Liquid: close, irregular, slide past one another. Gas: far apart, random, fast in all directions. (Paper 2 only)
What can heating a substance do to its stored energy?: Raise its temperature, or change its state. (Paper 2 only)
Why does the temperature stay constant during a change of state?: The energy supplied breaks the forces between particles instead of increasing their kinetic energy. On a temperature–time graph this is a flat section. (Paper 2 only)
Specific heat capacity: The energy needed to raise the temperature of 1 kg of a substance by 1 °C. ΔQ = m × c × ΔT. (Paper 2 only)
Energy to heat 2.0 kg of water (c = 4200 J/kg °C) from 20 °C to 100 °C?: ΔQ = mcΔT = 2.0 × 4200 × 80 = 672 000 J. (Paper 2 only)
Do particles expand when a solid is heated?: No. They vibrate more vigorously and take up more space; the particles themselves do not expand. (Paper 2 only)

What causes gas pressure?: Molecules in random motion collide with the container walls and exert a force on them.
Absolute zero: 0 K (−273 °C): the temperature at which molecules have minimum kinetic energy (not zero energy).
Kelvin temperature and molecular energy: T (K) = θ (°C) + 273. The kelvin temperature is directly proportional to the average kinetic energy of the molecules: doubling T doubles the average kinetic energy.
Gas at 2.0 × 10⁵ Pa and 0.30 m³ is compressed to 0.10 m³ at constant temperature. New pressure?: p₁V₁ = p₂V₂ (fixed mass, constant temperature): p₂ = 2.0 × 10⁵ × 0.30 ÷ 0.10 = 6.0 × 10⁵ Pa.
A fixed volume of gas at 1.0 × 10⁵ Pa is heated from 27 °C to 127 °C. New pressure?: p₁/T₁ = p₂/T₂ with T in kelvin: 300 K and 400 K. p₂ = 1.0 × 10⁵ × 400 ÷ 300 = 1.3 × 10⁵ Pa.
Particle explanation: reducing volume vs raising temperature: Smaller volume (constant T): molecules hit the walls more frequently, so pressure rises. Higher temperature (constant V): molecules move faster, hitting the walls more frequently and harder.