science; chapter 5

• what are the physical characteristics of pure water

  boiling point = 100°C

  freezing point = 0°C

  colourless

  density = 1 g cm-3
• cohesive force means attractive force between same molecules
• adhesive force means attractive force between different molecules
• surface tension is a result of cohesive force and water molecules at the surface
• capillary action is when (cohesive and adhesive force between water molecules) and (the cell walls of xylem water) draws up water from the roots to leaves of plants
• solid: heat is absorbed (melting) and turns into liquid

  liquid: heat is absorbed (evaporation/boiling) and turns into gas
• gas: heat is released (condensation) and turns into liquid

  liquid: heat is released (freezing) and turns into solid
• what is water? what is it made out of? how can you determine the composition of elements in a water molecule?

  • compound
  • oxygen and hydrogen combined chemically
  • through electrolysis
• anode: positive terminal of a battery

  cathode: negative terminal of a battery
• the molecules of water at the surface have higher kinetic energy, thus they can move faster and escape into the air (process of water evaporation)
• factors affecting the rate of evaporation of water:

  • humidity = dry air contains less water vapour and holds more water molecules
  • surrounding temperature = if the s.t increases, the water molecules at the surface gain more energy and ESCAPE INTO THE AIR
  • exposed surface area of water = the larger the e.s.a.o.w, the more it allows more water molecules to escape
  • movement of air = high speed of wind cause the air at the surface water to dry