The Properties of Water

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  • Properties of Water
    • Specific Heat Capacity
      • water molecules stick together by hydrogen bonding
        • takes lots of energy to separate them
      • this is why water has higher boiling point than predicted
      • presence of hydrogen bonds mean that water has highest specific heat capacity
      • amount of energy needed to change temperature of 1kg of substance by 1 degrees
      • SHC of pure water is 4910
    • Latent Heat of Vapourisation
      • when substance turns from liquids to gas it requires energy
      • potential energy stored in forces between molecules need to be overcome by kinetic energy of motion of particles before it changes phase
      • high degree of hydrogen bonding between molecules means lots of energy is required to evaporate 1g of water
        • LHoV
      • water has large LHoV
      • explains why sweating cools body
        • body rises above normal temp, sweat is secreted
        • water molecules in sweat gain energy
          • break free from bonds & become water vapour
            • as water evaporates heat energy removed from skin
              • loss of energy cools skin
          • as water has high LHoV lots of heat energy
    • Cohesion
      • tendency of molecules to stick together
      • hydrogen bonds mean water has large cohesive forces
      • allows to be pulled through tube
        • e.g. xylem, straw, pipette
    • Surface Tension
      • where water meets air the water molecules tend to be pulled back in to body of water
        • means water acts like a skin & is strong enough to support small organisms on surface
    • Water as a Solvent
      • solvent - liquid which dissolves solute
      • solute - substance dissolves in solvent
      • water is medium in which enzyme-catalysed reactions take place
      • readily dissolves substances
        • respiratory gases
          • oxygen & CO2
        • excretory products
          • ammonia & urea
        • inorganic ions
          • hydrogen & iron
        • small hydrophilic ions
          • amino acids & ATP
    • Water in Metabolism
      • water used in hydrolysis reactions to break down complex molecules
        • protein --> amino acids
      • formed in condensations reactions
        • starch & protein synthesis
      • raw material required in photosynthesis & a product of respiration


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