Water and Aqueous Systems

Transcription

1 Water and Aqueous Systems Chemistry CP propertiesofwater/water.html

2 The Water Molecule Bent Two lone electron pairs Polar molecule Considered to be the universal solvent Solutions: contain a solute and solvent Solute: gets dissolved Solvent: does dissolving

3 Polarity Water is a solvent because it s polar Oxygen atom in the water molecule has a high electronegativity Electrons shared by the hydrogen and oxygen atoms are more attracted to the oxygen Unequal attraction of electrons generates partial electric charges within the water molecule Oxygen atom has partial negative charge, and the hydrogen atoms have a partial positive charge

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5 Hydrogen Bonding Attractive interaction between a hydrogen atom and an electromagnetic atom (O, N,F) Hydrogen bonding is responsible for many of the unique properties of water such as: high surface tension low vapor pressure lower density in the solid form than in the liquid high specific heat

6 Surface Tension Is the result of unbalanced forces which exist on the surface of a liquid Submerged molecules are tugged in all directions But molecules on surface have no pull upward on them Surface tension is an inward force that causes the surface to behave as a skin Surface tension causes water to form nearly spherical droplets The higher the intermolecular forces the greater the surface tension

7 Surface Tension Surface tension causes water to form nearly spherical droplets

8 Surface Tension of Water

9 Capillarity Tendency for a liquid to rise spontaneously in a small tube Unbalanced forces experienced by surface molecules are alleviated by polar water molecules that are also attracted to tubes (Adhesion) Combination of forces pulls a film of water onto waters of tubes and water molecules that hang together (cohesion) move up into the tube

10 Water s Low Vapor Pressure Vapor Pressure: liquids exert pressure above their surfaces when placed in a closed container with space above them Molecules on surface have enough K.E. to escape the pull of intermolecular forces and leave liquid phase Their collisions with container generate pressure Related to speed of evaporation and strength of intermolecular forces

11 Water s Low Vapor Pressure Because of hydrogen bonds holding the water molecules together, molecules have low tendency to break free from the surface into the vapor phase

12 Density of Water Ice has a lower density than liquid water Maximum density of water happens at 4 O C (not as ice!)

13 Density of Water Most substances are denser in solid state than in liquid state In solid state, each molecule of water is hydrogen bonded to four other water molecules Forms an open crystal lattice with open space When ice melts, hydrogen bonds break Lattice collapses Water molecules move closer together and occupy less space

14 Specific Heat of Water Water has an extraordinarily high specific heat, or capacity to absorb energy Specific heat is measured as the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius Water s specific heat is unusually high because it contains many hydrogen bonds A large amount of energy is needed to break the hydrogen bonds between the molecules before heat is transferred

15 Specific Heat of Water A great deal of heat energy is require to change water s phase (or state) from solid ice to liquid or from liquid to gas (steam). When liquid water has absorbed enough energy to break all of the hydrogen bonds, it changes from a liquid to a gas-steam. Water vapor has the highest entropy ( S) of the three phases Entropy is a measure of disorder