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Colour

State atroomtemp.

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Specificheat

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Match the property of water with the corresponding significance for life and correctly fill in the table

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rProperty of water

Ice is less dense than water

High surface tension

Strong cohesive properties and high tensile strength

Colourless with a high transmission

Liquid at room temperature

In order to evaporate it must absorb a large amount of energy (high latent heat of vaporisation)

Water can absorb a lot of energy for only a small rise in temperature (high specific heat capacity)

Significance for life

Conditions are stable in cells and aquatic environments

Can be used for cooling organisms by evaporation of for example sweat

The high surface tension of water means that it can form a habitat on the surface of the water

Ice forms an insulating layer over water

Can be used for transport and a medium for reactions

Light can pass through cells for photosynthesis

Water can be pulled through plants in a column as the water molecules are held together by H-bonds

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rProperty of water

Ice is less dense than water

High surface tension

Strong cohesive properties and high tensile strength

Colourless with a high transmission

Liquid at room temperature

In order to evaporate it must absorb a large amount of energy (high latent heat of vaporisation)

Water can absorb a lot of energy for only a small rise in temperature (high specific heat capacity)

Significance for life

Conditions are stable in cells and aquatic environments

Can be used for cooling organisms by evaporation of for example sweat

The high surface tension of water means that it can form a habitat on the surface of the water

Ice forms an insulating layer over water

Can be used for transport and a medium for reactions

Light can pass through cells for photosynthesis

Water can be pulled through plants in a column as the water molecules are held together by H-bonds

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rSurface Tension

• The surface of water can behave like an elastic sheet

• The molecules in the bulk of the liquid are effected by various intermolecular forces of attraction

• Those molecules in the surface are not effected by molecules above them, and therefore ‘pull’ together more strongly, effectively resembling a stretched membrane

• A habitat can therefore survive on the surface of the water

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rColour – transmission of light

• Water is colourless and is therefore transparent to light

• This means that sunlight can reach the cells and pass through them so that photosynthesis may occur 53%

10%13%

9%

32%8%7%

7%

Reflected by leaves

Transmitted through leaves

Sun light

Light absorbed by leaves (typical values):

Near IR 15%

Red 82%

Green 80%

Blue 84% BackBack

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rCohesion

• Water molecules show a strong attraction to one another, this is called cohesion.

Droplets of water form spheres due to cohesion between water molecules

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rLatent heat

• While changing state, a substance will take in heat energy (solid liquid gas), or expel heat energy (gas liquid solid) without a change in temperature. This is termed Latent Heat.

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temperature

time

SOLI

D

LIQ

UID

GAS

melt

solidify

evaporate

condense

• Water has a large latent heat of vaporisation, and therefore absorbs a large amount of heat energy while changing from water to vapour.

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rState at room temperature

• Water is a liquid at room temperature. However, all other similar molecules are gases.

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• Hydrogen bonds act between the water molecules, and they attract them enough so that it behaves as a liquid.

H H

O++

2-

H H

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2-

H H

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H H

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Hydrogen bonds form because of polar covalent bonding between the oxygen and hydrogen atoms

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rSpecific Heat Capacity

• The heat needed to raise the temperature of 1kg of water by 1°C is termed the Specific Heat Capacity.

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1kg of water

• Water has a large specific heat capacity, and therefore can absorb large amounts of heat energy before its temperature raises a significant amount.

thermometer

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rDensity of water

• Unlike other substances, water expands as it freezes.

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• As water expands when it freezes, its density (mass per unit volume) will decrease.

• This means that ice is less dense than water, and will therefore float on top of it.

Water molecules are able to approach one another quite closely

H H

O

H H

OH H

OH H

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H H

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H H

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H H

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H H

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H H

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H H

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H H

O

Water molecules in ice form a rigid structure so that there is more space between them, this is seen as expansion as a wholeWater

Ice