Specific heat capacity
Energy = mass of water (KG) x 4200j kg•c x temp change
Latent heat of evaporation question
Energy = mass (kg) x 2260
Properties of water
- liquid between 0-100•C
- very high shc
- very high latent heat of evaporation and fusion
- solid water ice is less dense than liquid water highest density is at 4•C
- very high surface tension
- strong adhesion to surface
- strong cohesion between molecules
- low viscosity but not too low
- dissolves more substances than any other (universal solvent )
- high transmission of visible light (colourless)
- water and heat energy
Polarity
The polarity of water molecules allows hydrogen bonds to form between adjacent water molecules
Water has many essential roles in living organisms due to its properties:
The polarity of water molecules
The presence and number of hydrogen bonds between water molecules
Solvent
As water is a polar molecule many ions (e.g. sodium chloride) and covalently bonded polar substances (e.g. glucose) will dissolve in it
This allows chemical reactions to occur within cells (as the dissolved solutes are more chemically reactive when they are free to move about)
Metabolites can be transported efficiently (except non-polar molecules which are hydrophobic)
This process allows prokaryotic cells to exchange substances, such as nutrients and waste products, with their surroundings via the process of diffusion
High specific heat capacity
The specific heat capacity of a substance is the amount of thermal energy required to raise the temperature of 1kg of that substance by 1°C
Water’s specific heat capacity is 4200 J/kg°C meaning a relatively large amount of energy is required to raise its temperature
The high specific heat capacity is due to the many hydrogen bonds present in water. It takes a lot of thermal energy to break these bonds and a lot of energy to build them, thus the temperature of water does not fluctuate greatly
The advantage for living organisms is that it:
Provides suitable stable habitats in aquatic environments such as in lakes and the ocean
Is able to maintain a constant temperature as water is able to absorb a lot of heat without big temperature fluctuations
This is vital in maintaining temperatures that are optimal for enzyme activity in both prokaryotes and eukaryotes
Water in blood plasma is also vital in transferring heat around the body, helping to maintain a fairly constant temperature
As blood passes through more active (‘warmer’) regions of the body, heat energy is absorbed but the temperature remains fairly constant
Water in tissue fluid also plays an important regulatory role in maintaining a constant body temperature
Latent heat of vaporisation
In order to change state (from liquid to gas) a large amount of thermal energy must be absorbed by water to break the hydrogen bonds and evaporate
This is an advantage for living organisms as only a little water is required to evaporate for the organism to lose a great amount of heat
This provides a cooling effect for living organisms, for example the transpiration from leaves or evaporation of water in sweat on the skin
Cohesion and Adhesion
Hydrogen bonds between water molecules allows for strong cohesion between water molecules
This allows columns of water to move through the xylem of plants and through blood vessels in animals rather than individual molecules
This also enables surface tension where a body of water meets the air, these hydrogen bonds occur between the top layer of water molecules to create a sort of film on the body of water (this is what allows insects such as pond skaters to float)
Water is also able to hydrogen bond to other molecules, such as cellulose, which is known as adhesion
This also enables water to move up the xylem due to transpiration
