Particle Model of Matter

• What is the definition of density?

  The density is defined as the mass per unit volume.
• How is density mathematically expressed?

  Density is expressed as $\rho =$$\frac{m}{V}$.
• What are the units of density?

  The units of density are kilograms per metre cubed (kg/m³).
• What does density depend on?

  Density depends on the spacing of the atoms in matter.
• How do the densities of solids and liquids compare?

  Solids and liquids have similar densities as the space between particles does not change significantly.
• What is the main exception to the rule that liquids usually have a lower density than solids?

  The main exception is ice and water.
• Why do gases have a far lower density compared to solids and liquids?

  Gases have a far lower density because the spacing between atoms increases significantly, leading to a greater volume.
• What happens to mass during a change of state?

  Mass is conserved during a change of state.
• If 20g of liquid evaporates, how much does the gas produced weigh?


  The gas produced will also weigh 20g.
• Why are changes of state considered physical changes?

  They are considered physical changes because the material retains its original properties when reversed.
• What are the different changes of state?

  • Melting
  • Freezing
  • Evaporating
  • Condensing
  • Sublimation
• What is internal energy?

  Internal energy is the energy stored by particles (atoms and molecules) within a system.
• What forms can internal energy take?

  Internal energy takes the forms of kinetic energy and potential energy.
• What happens to the energy of particles when a system is heated?

  Heating increases the energy the particles have, which increases the internal energy.
• What is specific heat capacity?

  Specific heat capacity is the amount of energy required to raise the temperature of 1kg of a substance by 1°C.
• What is the formula for change in thermal energy?


  The formula is $\Delta E =$$m \times c \times \Delta T$.
• What does $\Delta E$ represent in the formula for change in thermal energy?


  $\Delta E$ represents the change in thermal energy, in joules (J).
• What does $c$ represent in the formula for change in thermal energy?


  $c$ represents the specific heat capacity, in joules per kilogram per degree Celsius (Jkg⁻¹°C⁻¹).
• What does $m$ represent in the formula for change in thermal energy?


  $m$ represents the mass in kilograms (kg).
• What does $\Delta T$ represent in the formula for change in thermal energy?


  $\Delta T$ represents the temperature change in degrees Celsius (°C).
• What is specific latent heat?

  Specific latent heat is the amount of energy needed to change the state of 1kg of a substance without a change in temperature.
• What is the specific latent heat of fusion?

  The specific latent heat of fusion is the energy required to melt or freeze a substance.
• What is the specific latent heat of vaporisation?

  The specific latent heat of vaporisation is the energy required to boil or condense a substance.
• What is the formula for energy for a change of state?

  The formula is $E =$$m \times L$.
• What does $E$ represent in the formula for energy for a change of state?


  $E$ represents the energy in joules (J).
• What does $m$ represent in the formula for energy for a change of state?


  $m$ represents the mass in kilograms (kg).
• What does $L$ represent in the formula for energy for a change of state?


  $L$ represents the specific latent heat in joules per kilogram (J/kg).
• What happens to energy during melting and evaporating?


  Energy is absorbed when melting and evaporating.
• What happens to energy during freezing and condensing?

  Energy is released when freezing and condensing.
• What is sublimation?


  Sublimation is when a solid goes straight to gas.
• What is an example of sublimation?


  An example of sublimation is dry ice (solid CO₂) going directly to gas.
• What does the temperature graph of ice show at different points?

  • At A: Solid
  • At B: Reaches 0°C
  • From B to C: No temperature change (energy used for melting)
  • From C to D: Liquid state
  • From D to E: Water boiling (takes longer)
  • From E to F: Gas heating
• How is the temperature of a gas related to the average kinetic energy of its molecules?


  The temperature of the gas is related to the average kinetic energy of the molecules; higher temperature means greater average kinetic energy.
• What happens when gas molecules collide with the walls of their container?

  When gas molecules collide with the walls of their container, they exert a force on the wall, contributing to gas pressure.
• What is the Pressure law?

  The Pressure law states that changing the temperature of a gas, held at constant volume, changes the pressure exerted by the gas.
• How does changing the volume of a gas affect its pressure?

  Changing the volume of a gas affects the pressure; increasing the volume leads to a decrease in pressure.
• What is Boyle's law?

  Boyle's law states that increasing the volume of a gas at constant temperature leads to a decrease in pressure.
• What is the formula for Boyle's law?

  The formula is $P_1 V_1 =$$P_2 V_2$.
• What happens when work is done on a gas?

  Doing work on a gas increases its temperature.
• How does adding more particles to a fixed volume affect pressure?

  Adding more particles to a fixed volume increases the pressure due to more collisions with the walls.