Latent Heat Capacity

• What is required to change the state of a substance?

  Energy
• What happens to temperature during a change of state?

  There is no temperature change
• What is the term for energy supplied to change the state?

  Latent heat

  
• How is latent heat defined?

  Energy to change 1 kg without temperature change

  
• What are the two types of latent heat?

  • Specific latent heat of fusion (melting)
  • Specific latent heat of vaporisation (boiling)

  
• Why is specific latent heat defined by 1 kg?

  Because larger mass requires more energy
• What does the horizontal line of latent heat of fusion represent?

  Melting or freezing process

  
• What does the horizontal line of latent heat of vaporisation represent?

  Evaporation or condensation process

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

  Energy to convert 1 kg solid to liquid
• What does latent heat of fusion apply to?

  • Melting a solid
  • Freezing a liquid
• What is the specific latent heat of vaporisation defined as?

  Energy to convert 1 kg liquid to gas
• What does latent heat of vaporisation apply to?

  • Vaporising a liquid
  • Condensing a gas
• What is the formula to calculate the amount of energy required to change state?

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

  Q is energy, m is mass, L is 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
• Why does evaporating water require more energy than melting ice?

  Due to stronger intermolecular forces
• What does vaporisation do against atmospheric pressure?

  It does work
• What happens during thermal equilibrium?

  • Both substances reach the same final temperature
  • Energy is transferred between substances
• What happens to energy when ice is dropped into a warm drink?

  Energy is transferred to the ice
• How is the energy change indicated in calculations?

  With a negative sign
• What does ΔQcolder represent?

  Energy to raise temperature of colder material
• What does ΔQwarmer represent?

  Energy released by warmer material
• What must be included in calculations if a material changes phase?

  The phase change energy
• What is the equation for energy when a solid melts?

  ΔQcolder,solid + ΔQmelting + ΔQcolder,liquid = −ΔQwarmer
• What does ΔQmelting represent?

  Energy needed for phase change, melting
• What is the first step in calculating specific latent heat from energy needed?

  Write the thermal energy equation
• How do you rearrange Q = mL for latent heat?

  L = Q/m
• What is the mass of 530 g in kg?

  $0.530 \text{ kg}$
• What is the energy in joules for 0.6 MJ?

  $0.6 \times 10^6 \text{ J}$
• What is the specific heat capacity of coffee?

  $4180 \text{ J/kg K}$
• What is the specific heat capacity of ice?

  $2090 \text{ J/kg K}$
• What is the latent heat of fusion of ice?

  $334 \text{ J/g}$
• What happens to the energy of molecules during a phase change?

  • No change in temperature
  • Potential energy changes, not kinetic energy
• What causes the heat absorbed in melting and boiling?

  Overcoming intermolecular forces of attraction
• What happens to the intermolecular forces during freezing and condensation?

  They become stronger
• What is proportional to temperature in terms of energy?

  Kinetic energy
• What must happen if there is no change in temperature?

  No change in kinetic energy