boiling point and melting point m3

• Boiling Point (BP)


  The temperature at which the vapor pressure of the substance equals the pressure of the atmosphere above it
• Boiling Point


  • It is a physical constant that can be used in identification and characterization, as well as a criterion of purity of a substance
• Pure compounds


  Have a constant boiling point
• Mixtures


  Have a boiling point range except for azeotropes
• Compounds involving ionic bonds


  Have higher boiling point because the amount of heat required to separate the ions is higher than the amount required to separate molecules in covalent compounds
• Factors That Affect the Boiling Point


  • Strength of intermolecular forces
  • Length of carbon-carbon chain
  • Branching decreases the boiling point
  • Polarity
  • Impurities
• Non-volatile impurities


  Usually increase the boiling point of the liquid due to a decrease in the vapor pressure
• Volatile impurities


  Usually decrease the boiling point of the liquid
• Melting Point (MP)


  The temperature at which a solid melts and becomes a liquid
• Melting Point


  • Depends on the structure of the molecule involved - an example of the relationship between structure and properties
• Melting Point


  • Confirmation of synthesized organic compounds, however now different spectral techniques are also available (like IR, NMR and Mass Spectroscopy) but melting point confirmation through reference melting point is an economical, easy and convenient way for confirming the synthesized compound
• Factors That Affect the Melting Point


  • Molecular Symmetry
  • Molecular Size
  • Polarity/Intermolecular Forces
  • Impurities
• Molecular Symmetry


  • Conformation and Orientation (Linear vs Branched)
  • Odd vs Even chain length
• Molecular Size


  • Length of carbon-carbon chain
• The higher the molecular mass, the greater the intermolecular forces between molecules.
• At high temperatures, particles have enough energy to overcome weak intermolecular forces and break free from their neighbors.
• Increasing temperature increases kinetic energy, causing particles to move faster and collide more frequently with other particles.
• This means that larger molecules have stronger intermolecular forces than smaller ones.
• Increasing the number of atoms in a molecule increases its size and therefore the strength of the intermolecular forces.
• As temperature increases, more and more particles gain sufficient kinetic energy to escape from neighboring particles.
• Increasing temperature causes particles to vibrate faster and collide with one another more frequently.
• Substances that are solid or liquid at room temperature can be converted into gases by heating them until they reach their boiling points.
• When the average kinetic energy is sufficient to overcome the attractive forces holding particles together, the substance undergoes a phase change.
• As temperature increases, the average kinetic energy of particles also increases, allowing them to overcome these strong intermolecular forces and separate into individual molecules or atoms.
• Intermolecular Forces are responsible for holding molecules together in solids and liquids.
• As the number of atoms in a molecule increases, so does the strength of the intermolecular forces.
• Stronger Intermolecular Forces require higher Temperatures to be broken apart.
• Intermolecular Forces are attractive or repulsive forces acting between molecules.
• Melting points increase as the strength of the intermolecular forces increases.
• The higher the boiling point, the greater the strength of the intermolecular forces between particles.
• Melting point is also related to the strength of the intermolecular forces between particles.
• Boiling points also increase as the strength of the intermolecular forces increases.
• Boiling point is directly proportional to the strength of the intermolecular forces between particles.
• The higher the molecular mass of a compound, the greater the force between the molecules and the higher the boiling point will be.
• Boiling point is related to the strength of the intermolecular forces between particles.
• Melting Point - The temperature at which a solid changes directly into a liquid without passing through an intermediate state (e.g., gas).
• Boiling Point - The temperature at which a liquid changes directly into a gas without passing through an intermediate state (e.g., solid).
• The stronger the intermolecular forces between particles, the higher the boiling point of the substance will be.
• Boiling point is the temperature at which the vapor pressure of a liquid equals atmospheric pressure.
• The strength of Intermolecular Forces depends on the type of bond between the molecules.