Hydrogen bonding and water

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  • Created by: J.E.C.
  • Created on: 01-05-14 17:37
Hydrogen bonding in water is particularly strong because...?
There are two lone pairs and two positively charged hydrogen atoms per oxygen atom.
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Give 3 unusual properties of water?
1. High bp and enthalpy change of vaporisation 2. Greater SHC than most other liquids 3. Decrease in density when it freezes
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What is enthalpy change of vaporisation?
Energy required to put into a liquid to overcome the intermolecular bonds and turn one mole of molecules from liquid to vapour.
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Explain why hydrogen bonds in ammonia are not as effective as those in H2O and HF?
Nitrogen is not as highly electronegative as fluorine or oxygen, so the hydrogen bonds that form (only one per molecule) are not as effective.
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Define specific heat capacity?
Energy needed to raise 1g of a substance through 1 K.
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Why does water have an unusually high specific heat capacity?
Much energy needed to overcome the hydrogen bonds between clusters of water molecules. Therefore the energy supplied does not raise the kinetic energy, instead it is used in breaking the bonds.
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Explain what happens to water as it approaches freezing temperature?
At 4°C the water contracts and its volume decreases. The water expands as its temperature reaches 0°C and there is a further expansion when it freezes.
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What is the arrangement of atoms in ice, and the consequences of this?
The 4 groups around each oxygen are arranged tetrahedrally in 3 dimensions. This maximises hydrogen bonding between water molecules, and creates a large open structure with large spaces in it.
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Explain why density increases when ice melts?
The open structure collapses and the water molecules fall into some of the open spaces, giving it a greater density.
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Other cards in this set

Card 2

Front

Give 3 unusual properties of water?

Back

1. High bp and enthalpy change of vaporisation 2. Greater SHC than most other liquids 3. Decrease in density when it freezes

Card 3

Front

What is enthalpy change of vaporisation?

Back

Preview of the front of card 3

Card 4

Front

Explain why hydrogen bonds in ammonia are not as effective as those in H2O and HF?

Back

Preview of the front of card 4

Card 5

Front

Define specific heat capacity?

Back

Preview of the front of card 5
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