Topic 14 – Particle model

• • Solids: Particles vibrate in fixed positions, arranged closely in a regular pattern.
  • Liquids: Particles move freely but remain in contact, close together but not fixed.
  • Gases: Particles move freely and randomly, far apart with no regular arrangement.
• What is the density formula?

  $p =$$m / v$(mass is in kg while volume is in $m^3$)
• What is the method used for finding the density of solids and liquids?

  1. Measure object mass (m1) with a balance.
  2. Fill bottle with known-density liquid (e.g., water) and seal with stopper.
  3. Dry bottle exterior and measure mass (m2).
  4. Empty bottle and place object inside.
  5. Repeat steps 2-3, measuring mass with object (m3).
  6. Calculate volume of displaced water:

  • Mass of displaced water = m2 - (m2 - m3).
  • Use density of water (known) to find volume: V = m / ρ.

  1. Calculate object density using ρ = m1 / V (mass from step 1, volume from step 6).
• • Solids: Atoms/molecules tightly packed in fixed arrangement, high density.
  • Liquids: Atoms/molecules less tightly packed, can move past each other, lower density.
  • Gases: Atoms/molecules widely spaced, move freely, lowest density.
• when substances melt, freeze, evaporate, boil, condense or sublimate mass is conserved and these physical changes differ from some chemical changes because the material recovers its original properties if the change is reversed.
• Heating a system will change the energy stored within the system and raise its temperature or produce changes of state.
• What is the definition of specific heat capacity?

  The specific heat capacity of a material is the energy required to raise one kilogram (kg) of the material by one degree Celsius (°C).
• What is the formula for specific heat capacity?

  $ΔQ =$$m *$$c *$$Δθ$ where $Q$is energy (J) $c$is specific heat capacity (J/kg) and $θ$is temperature (C).
• What is the definition of specific latent heat?

  The specific latent heat of a substance is the amount of energy needed to change the state of 1 kg of the substance without changing its temperature.
• What is the formula for specific latent heat?

  $Q =$$M *$$L$where $Q$ is thermal energy and $L$ is specific latent heat.

  
• Explain ways of reducing unwanted energy transfer through thermal insulation:

  • Increase thickness: A Longer pathway for heat to travel.
  • Choose low thermal conductivity materials: Reduce conduction rate.
  • Trap air pockets: Inhibit convective heat transfer.
  • Use reflective surfaces: Reflect heat radiation.
  • Ensure tight seals: Prevent convection and air infiltration.
  • Install double glazing: Reduce conduction and convective currents.
• What is the method for finding the specific heat capacity of water?

  1. Measure insulating container mass with a mass balance.
  2. Fill container with water and measure mass difference.
  3. Set up experiment, ensuring joulemeter reads zero.
  4. Measure water temperature, then turn on power.
  5. Monitor temperature until desired increase, then record energy and temperature rise.
  6. Calculate water's specific heat capacity using collected data.
  7. Repeat experiment multiple times for an average result.
• What experiment is used for visualising the change of state in water?

  1. Fill beaker with crushed ice.
  2. Record initial ice temperature using thermometer.
  3. Gradually heat beaker with Bunsen burner.
  4. Record temperature and ice state every twenty seconds.
  5. Continue heating until water begins to boil.
  6. Plot temperature vs. time graph for experiment.

  
• Explain the pressure of a gas in terms of the motion of its particles:

  • Gas particles are in constant, random motion.
  • Collisions with container walls transfer momentum.
  • Increased particle speed leads to higher pressure.
  • Pressure is proportional to collision frequency and force.
  • Boyle's law: Pressure inversely proportional to volume at constant temperature
• What is the effect of temperature on gas particles?

  • Higher temperature increases particle velocity.
  • Faster particles collide with container walls more frequently.
  • Increased collision frequency results in higher pressure for a fixed mass of gas at constant volume.
• Describe the term absolute zero, −273 °C, in terms of the lack of movement of particles:

  • Absolute zero: Lowest possible temperature.
  • Particles have minimal kinetic energy.
  • Particle movement ceases entirely.
  • Corresponds to 0 Kelvin on the Kelvin scale.
  • Complete absence of thermal motion and energy.
• 0 kelvin = -273 Celsius.
• Gases can be compressed or expanded by pressure changes.
• The pressure of a gas produces a net force at right angles to any surface.

  
• • Decreasing gas volume increases collision frequency with container walls.
  • Higher collision frequency leads to higher pressure.
  • Increasing gas volume decreases collision frequency.
  • Lower collision frequency leads to lower pressure.
  • Described by Boyle's Law: pressure is inversely proportional to volume at a constant temperature.
• What formula is used to calculate pressure or volume for gases of fixed mass at constant temperature?

  $P1 ×V1 =$$P2 ×V2$

  
• • Doing work on a gas increases its internal energy, raising its temperature.
  • Mechanical work, like using a bike pump, adds energy to gas particles.
  • Gas exerts pressure on the pump, requiring work to push the plunger.
  • Work transfers energy to gas particles, increasing their kinetic energy and temperature.
  • Energy transferred to connected objects, like a tyre, can raise their temperature.