6.4 Energy of Phase Changes

• Exothermic phase changes release energy.


  True
• What overcomes intermolecular forces during phase changes?

  Energy
• What is the enthalpy of fusion for water (H2O)?

  6.01 kJ/mol
• Order the phase changes by the type of energy required or released:

  1️⃣ Melting (requires energy)

  2️⃣ Boiling (requires energy)

  3️⃣ Freezing (releases energy)

  4️⃣ Condensation (releases energy)

  5️⃣ Sublimation (requires energy)
• The enthalpy of fusion represents the energy required to change a substance from solid to liquid
• The enthalpy of fusion is typically expressed in units of kJ/mol or kcal/mol
• Phase changes occur when a substance absorbs or releases energy.


  True
• What is the enthalpy of fusion for water (H2O)?

  6.01 kJ/mol
• Match the phase change with its energy requirement:

  Melting ↔️ Requires energy (endothermic)

  Freezing ↔️ Releases energy (exothermic)
• Condensation is an exothermic process.

  True
• Common phase changes include melting, boiling, freezing, condensation, and sublimation
• The enthalpy of fusion is generally lower than the enthalpy of vaporization
• Phase changes can be either endothermic or exothermic
• The enthalpy of fusion for water is 6.01 kJ/mol, while the enthalpy of vaporization is 40.7 kJ/mol
• The melting of ice is an endothermic process because it absorbs energy
• Steps to calculate energy changes during phase transitions:

  1️⃣ Identify the phase change

  2️⃣ Multiply the moles by the enthalpy value

  3️⃣ Determine if energy is required or released
• The enthalpy of vaporization for water is higher than its enthalpy of fusion.

  True
• What must energy overcome during phase changes to allow transitions between solid, liquid, and gas states?

  Intermolecular forces
• Which phase change involves a substance directly transitioning from solid to gas?

  Sublimation
• The enthalpy of fusion is expressed in kJ/mol.


  True
• The enthalpy of vaporization for water (H2O) is 40.7 kJ/mol.


  True
• Endothermic phase changes absorb energy.


  True
• Calculating energy changes during phase changes requires multiplying the moles of substance by the corresponding enthalpy value.

  True
• In freezer operation, what type of energy change occurs during water freezing?

  Exothermic
• What do phase changes refer to?

  Transitions between states of matter
• Phase changes occur when the energy of the system is increased or decreased
• Adding heat energy to a solid can cause it to melt.


  True
• Match the enthalpy type with its description:

  Enthalpy of fusion ↔️ Energy to change solid to liquid

  Enthalpy of vaporization ↔️ Energy to change liquid to gas
• The enthalpy of fusion measures the energy required to change a substance from solid to liquid
• What is the enthalpy of vaporization for water (H2O)?

  40.7 kJ/mol
• The phase change from solid to liquid is called melting
• What is the enthalpy of fusion for water (H2O) in kJ/mol?

  6.01
• What does the enthalpy of vaporization depend on primarily?

  Intermolecular forces
• Which phase change is an example of an endothermic process?

  Melting
• What is the energy required to melt 2.5 mol of ice at 0°C using the enthalpy of fusion for water?

  15.025 kJ
• To melt 3 moles of ice, 18.03 kJ of energy is required.


  True