Water

• Water forms hydrogen bonds with other molecules between the slightly positive hydrogens and the negative lone pair of electrons of the other molecule‘s oxygen.
• Why does water have a high boiling point?

  The hydrogen bonds in between molecules are difficult to break, and so require a lot of energy.
• Why does water become less dense when frozen?

  As water is cooled below 4•C, the hydrogen bonds fix the positions of the polar molecules slightly further apart than the averge distance in liquid state.
• Cohesion in water


  The hydrogen bonds cause molecules to stick together.
• Water acts as a solvent in which many solutes can be dissolved, as many solutes are polar, like water.
• Water makes a very efficient transport medium within living organisms. Cohesion means that when water is transported through the body, molecules will stick together.
• Adhesion in water. 


  Adhesion occurs between water molecules and other polar molecules and surfaces. The effects of adhesion and cohesion result in water exhibiting capillary action.
• Capillary action. 


  The process by which water can rise up a narrow tube against the force of gravity.
• The importance of cohesion and surface tension to living organisms. 


  Surface tension allows some living organisms to walk on water, slows down water loss in plants, and attraction makes water less likely to evaporate, allowing large bodies of water to collect and remain a viable environment for life.
• The importance of water being a good solvent to living organisms. 


  Water helps cells transport and use substances like oxygen or nutrients. Water is capable of dissolving more substances than any other liquid, and enables plants to pick up nutrients and move them around.
• Specific heat capacity of water. 


  Water requires 4.2J of energy to raise 1•C in temperature.

  This is high as, when heat is absorbed, hydrogen bonds are broken and water molecules can move more freely. As a long time to heat and a long time to cool.
• The importance of water’s specific heat capacity to living organisms. 


  Water resists sudden changes in temperature, which makes water an excellent habitat, allowing organisms to survive without experiencing wide temp fluctuations.
• Surface tension is a measure of the force attraction among molecules at the surface of a liquid. Surface tension allows some living organisms to walk on water, slows down water loss in plants, and attraction makes water less likely to evaporate, allowing large bodies of water to collect and remain a viable environment for life.

   
• Cohesion refers to the attraction that molecules have for others of the same type. Water molecules have strong cohesive forces because of their ability to form hydrogen bonds with one another.
• Latent heat

  The amount of energy required to change the state of a substance without changing its temperature
• Water

  • High latent heat
  • Due to network of hydrogen bonding amongst water molecules
  • High input of energy required to transform liquid water into water vapour
• Hydrogen bonding


  Makes it difficult to separate water molecules from each other, which is required for water to enter its gaseous phase
• Water

  Acts as a heat sink and so requires much more heat to boil
• Water evaporation

  1. Energy is taken up by the process

  2. Cooling the environment where evaporation is taking place
• Organisms, including humans

  • Evaporation of sweat (90% water) allows the organism to cool
  • Maintains homeostasis of body temperature
• A metabolite is a molecule that takes part in a metabolic reaction. water is often a reactant necessary to start a metabolic reaction and is often a byproduct of these reactions. Water is a key metabolite in condensation and hydrolysis reaction. A metabolic reaction is a biochemical reaction that takes place in a living organism to keep them alive.
• Water is transparent because it does not absorb or scatter much light at visible wavelengths. Water is a polar molecule that lets light through relatively easily. Water is also optically homogenous, which means it has the same refractive index throughout. Aquatic plants need sunlight for photosynthesis - the clearer the water, the deeper sunlight will penetrate. The sun is a source of energy to all biological phenomena. When light attenuates, it alters or limits the capacity of life for some biological communities.
• When the temperature lowers, there is not enough energy to break hydrogen bonds, so water molecules form a crystalline structure maintained by hydrogen bonding. this makes ice less dense that liquid water - hydrogen bonds push molecules further apart. When ice forms on the surface of lakes or ponds, it creates an insulating barrier that protects animals and plant life from freezing (living organisms cannot survive being frozen as ice crystals that form upon freezing rupture delicate membranes. Calls can only survive if water is temporarily replaced).