Internal energy & energy transfers

• What is internal energy defined as?

  Total energy stored inside a system
• What are the two types of energy stored in molecules?

  Kinetic and potential energy
• What does the kinetic store of energy in molecules depend on?

  Random motion and vibration of particles
• What does the potential store of energy in molecules depend on?

  Position relative to each other
• How does heating a system affect its internal energy?

  It increases the kinetic energy of particles

  
• How is temperature related to the average kinetic energy of molecules?

  Higher temperature means higher kinetic energy
• What happens to gas molecules as the container is heated?

  They move faster with higher kinetic energy

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

  Energy transfers to the potential store instead
• What is the effect of energy transfer during a change of state?

  Temperature remains constant during the change
• What happens to the potential energy of molecules during a change of state?

  It increases to overcome intermolecular forces
• What is the latent heat?

  Energy needed for a substance to change state

  
• What are the two types of latent heat?

  Latent heat of fusion and vaporisation

  
• What is specific latent heat defined as?

  Energy required to change 1 kg of substance
• What is the specific latent heat of fusion?

  Energy to convert 1 kg between solid and liquid
• What is the specific latent heat of vaporisation?

  Energy to convert 1 kg between liquid and gas
• How is the energy transferred during melting or boiling?

  Temperature remains constant during the process
• What is the equation to calculate the change in energy?

  ΔE = mcΔθ
• If the mass of water is 0.48 kg and the temperature change is 0.7 °C, what is the energy transferred?

  1400 J
• What is the significance of specific heat capacity in materials?

  Determines how quickly a substance heats up

  
• Why is water's specific heat capacity high?

  It retains heat for a long time
• What is the role of specific heat capacity in kitchen appliances?

  Helps choose materials for efficient heating

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

  It remains constant despite energy transfer
• What is the latent heat of fusion used for?

  Changing state between solid and liquid

  
• What is the latent heat of vaporisation used for?

  Changing state between liquid and gas

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

  It remains constant until fully vaporised
• What is the effect of latent heat on temperature during state changes?

  Temperature does not change during state changes
• What is the specific latent heat of vaporisation defined as?

  Energy to convert 1 kg liquid to gas
• What happens to the temperature of a liquid during vaporisation?

  The temperature stays constant until vaporised
• What is the latent heat of vaporisation used for when a gas condenses?

  Energy transferred away until liquid state
• What is the temperature at which a gas condenses?

  Same as its boiling point
• Why is it important to include 'with no change in temperature' in the definition of specific latent heat?

  To be awarded full marks in exams
• How can you remember the difference between latent heat of fusion and vaporisation?

  • Latent heat of fusion: 'fusing' liquid to solid
  • Latent heat of vaporisation: vaporising liquid to gas

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

  Energy that appears hidden during state changes

  
• What is the formula for calculating the energy required for a change in state?

  E = mL
• What do the variables in the equation E = mL represent?

  E = energy, m = mass, L = latent heat
• What is the specific latent heat of fusion for water?

  330 kJ/kg

  
• What is the specific latent heat of vaporisation for water?

  2.26 MJ/kg
• How much more energy is required to evaporate 1 kg of water compared to melting the same amount of ice?

  Seven times more energy
• How would you calculate the energy transferred as 0.60 kg of stearic acid changes from liquid to solid?

  Use E = mL with L = 199,000 J/kg
• What happens to the temperature of a solid when energy is transferred to it?

  The temperature starts to increase