Internal Energy & Energy Transfers

• What is internal energy defined as?

  The total energy stored inside a system by the particles that make up the system due to their motion and positions
• What are the two types of energy that contribute to the internal energy of molecules?

  Kinetic energy and potential energy
• How does heating a system affect the internal energy of a substance?

  It increases the kinetic energy of its particles

  
• What is the relationship between temperature and the average kinetic energy of molecules?

  The temperature is related to the average kinetic energy of the molecules
• What happens to the kinetic energy of gas molecules as the container is heated?

  The gas molecules move faster with higher kinetic energy

  
• What occurs when a substance reaches a certain temperature during heating?

  Energy is transferred to the potential store of the molecules instead of the kinetic store
• What is the effect of energy transfer on intermolecular forces during a change of state?

  It is used to overcome the intermolecular forces of attraction between the molecules
• What happens to the potential energy of molecules when a substance changes state?

  The potential energy of the molecules increases
• What is the specific heat capacity?

  The amount of energy required to raise the temperature of 1 kg of the substance by 1 °C
• How does the specific heat capacity affect the heating and cooling of substances?

  A low specific heat capacity means a substance heats up and cools down quickly

  
• Why is water considered ideal for heating homes?

  Because it has a very high specific heat capacity, allowing it to remain hot for a long time

  
• What is the equation to calculate the change in energy when heating a substance?

  ΔE = mcΔθ
• If the mass of a substance is 0.48 kg and the change in temperature is 0.7 °C, what is the energy transferred if the specific heat capacity is 4200 J/kg °C?

  ΔE = 1400 J
• What is latent heat?

  The energy needed for a substance to change state

  
• What happens to the temperature of a substance during a change of state?

  The temperature remains constant despite energy being transferred

  
• What are the two types of latent heat?

  Latent heat of fusion and latent heat of vaporisation

  
• What is specific latent heat defined as?

  The amount of energy required to change the state of 1 kg of a substance with no change in temperature
• What is the specific latent heat of fusion?

  The energy required to convert 1 kg of a substance between a solid and a liquid state with no change in temperature

  
• What is the specific latent heat of vaporisation?

  The energy required to convert 1 kg between a liquid and a gaseous state with no change in temperature

  
• What happens to the temperature of a substance when it is vaporised?

  The temperature will stay constant until all of the substance has vaporised
• What is the latent heat of fusion related to?

  The energy needed for all particles in a substance to overcome intermolecular forces during melting or freezing
• What is the latent heat of vaporisation related to?

  The energy needed for all particles in a substance to overcome intermolecular forces during vaporisation or condensation

  
• What is the specific latent heat of vaporisation defined as?

  The energy required to convert 1 kg between a liquid and a gaseous state with no change in temperature

  
• When does the temperature of a liquid substance stay constant during vaporisation?

  Until all of the substance has vaporised
• What does the latent heat of vaporisation represent?

  The amount of energy per kg needed for all particles to overcome intermolecular forces in the liquid state

  
• At what temperature does a gas condense?

  At the same temperature as its boiling point
• What happens to the latent heat of vaporisation when a gas condenses?

  It is the amount of energy per kg transferred away from the substance until all particles are in the liquid state

  
• What should you include in your definition of specific latent heat to receive full marks?

  'With no change in temperature'
• How can you remember the difference between latent heat of fusion and latent heat of vaporisation?

  • Latent heat of fusion: Imagine ‘fusing’ liquid molecules into a solid
  • Latent heat of vaporisation: Imagine vaporising liquid molecules into a gas

  
• What does the term 'latent' mean in the context of latent heat?

  It means hidden
• What happens to the temperature of a substance during melting?

  The temperature stops increasing as energy is used to overcome intermolecular forces
• What occurs when a substance reaches its boiling point during heating?

  The temperature stops increasing as energy is used to overcome intermolecular forces in the liquid state
• What is the process called when a gas turns back into a liquid?

  Condensation
• What happens to the temperature of a gas when energy is transferred away?

  The temperature starts to decrease as the particles lose kinetic energy
• What is the term for the process when a liquid turns back into a solid?

  Freezing
• What happens to the temperature of a liquid when energy is transferred away?

  The temperature starts to decrease as the particles lose kinetic energy

  
• What is the specific latent heat equation?

  E = mL

  
• What does 'E' represent in the specific latent heat equation?

  Thermal energy required for a change in state, in joules (J)

  
• What does 'm' represent in the specific latent heat equation?

  Mass, in kilograms (kg)

  
• What does 'L' represent in the specific latent heat equation?

  Specific latent heat, in joules per kilogram (J/kg)