section 2.4
1)cohesion
1) Hydrogen bonding keeps water molecules close to each other, and this cohesion helps pull water upward in the microscope vessels of plants. Hydrogen bonding is also responsible for water's surface tension.
Four emergent properties of water contribute to earth's fitness for life
1)cohesion 2)moderation of temperature 3)insulation of bodies of water by floating ice 4)the solvent of life
3) Insulation of bodies of water by floating ice
3) Ice floats because it is less dense than liquid water. This allows life to exist under the frozen surfaces of lakes and polar seas.
2) moderation of temperature
2) water has a high specific heat: heat is absorded when hydrogen bonds break and is released when hydrogen bonds form.
4) the solvent of life
4) Water is an unusually versatile solvent because its polar molecules are attracted to charged and polar substances capable of forming hydrogen bonds. Hydrophilic substances have an affinity for water; hydrophobic substances do not.
acidic and basic conditions affect living organisms
A water molecule can transfer an H+ to another water molecule to form H3O+ (represented simply by H+) and OH-
This is a dynamic equilibrium;reactions are still going on,but with no net effect on the concentrations of reactants and products.
Equilibrium does not mean that the reactants and products are equal in concentration, but only that their concentrations have stabilized at a particular ratio.
A hydrogen bond forms when the slightly negatively charged oxygen of one water molecule is attracted to the slightly positively charged hydrogen of a nearby molecule.
Hydrogen bonding between water molecules is the basis for water's unusual properties.
Coefficients indicates the numbers of molecules involved;for example, the coefficient 2 in front of the H2 means that the reaction starts with two molecules.
Notice all atoms of the reactants must be accounted for in the products. Matter is conserved in a chemical reaction:reactions cannot create or destroy matter but can only rearrange it.
The making and breaking of chemical bonds, leading to changes in the composition of matter, are called chemical reactions.
Reactions breaks the covalent bonds of H2 and O2 forms the new bonds of H2O. When we write a chemical reaction, we use an arrow to indicate the conversion of the starting materials, called the reatants, to the products.
Threats to water quality on Earth
The burning of fossil fuels results in emission of oxides (leading to acid precipitation) and increased amounts of CO2. Some CO2 become dissolved in the oceans, lowering pH and potentially affecting the rate of calcification on coral reefs.
One of the factors affecting the rate of a reaction is the centration of reactants. The greater the concentration of reactant molecules,the more frequently they colide with one another and have the opportunity to react and form products.
The forward and reverse reactions occur at the same rate, and the relative concentrations of products and reactants stop changing. The point at which the reactions offset one another exactly called chemical equilibrium.
