specific latent heat

• What is the energy needed to change the state of a substance called?

  Latent heat
• What happens to energy when a substance is melting or boiling?

  Energy is used to break bonds
• What does the energy transformed by heating not do during a change of state?

  It does not change the temperature
• What occurs when a substance is condensing or freezing?

  Bonds form, releasing energy
• What happens to internal energy during freezing?

  It decreases
• When does the temperature not decrease during freezing or condensing?

  Until all substance changes state
• What is specific latent heat (SLH)?

  • Energy needed to change 1 kg of substance
  • Occurs without changing temperature
• What is the specific latent heat of fusion?

  Energy for solid to liquid change
• What is the specific latent heat of vaporisation?

  Energy for liquid to gas change
• What is the formula for calculating energy needed for a change of state?

  Energy (E) = Mass (m) × Specific Latent Heat (l)

  • Energy in joules (J)
  • Mass in kg
  • SLH in J/kg
• If the mass is 250 g, how do you convert it to kg for calculations?

  Divide by 1000
• How much energy is needed to melt 250 g of a substance with SLH of 120,000 J/kg?

  $30,000 \text{ J}$
• What is the significance of the flat parts of a temperature-time graph during a change of state?

  They show energy transfer without temperature change
• How does the specific latent heat of fusion differ from that of vaporisation?

  Fusion is solid to liquid; vaporisation is liquid to gas
• Why is it important to know the specific latent heat for different materials?

  It varies for different materials and states
• What units are used for specific latent heat?

  J/kg
• What happens to temperature during a change of state?

  It remains constant
• How do the processes of melting and boiling differ in terms of energy usage?

  Both require energy to break bonds