Ch 10 Section 5 Flashcards
water is the most abundant
liquid
oceans, rivers, and lakes cover about
75% of earth’s surface
water is an essential component of all organisms: 70% to 90% of the mass of living things is
water
the chemical reactions of most life processes takes place in water, and water is frequently a
reactant or product in such reactions
water molecules consist of two atoms of hydrogen and one atom of
oxygen united by polar-covalent bonds
water molecule shape:
bent
the angle between the two hydrogen-oxygen bonds is about
105 degrees
this is close to the angle expected for … of the oxygen-atom orbitals
sp3 hybridization
the molecules in solid/ liquid wate rare linked by
hydrogen bonding
the number of linked molecules decreases with increasing temperature because increases in kinetic energy make
hydrogen bond formation difficult
nevertheless, there are usually from … to … molecules per…
4 to 8; group in liquid water
if it were not for these molecular groups, water would be a
gas at room temperature
nonpolar molecules, such as methane, that are similar in size and mass to water molecules do not
undergo hydrogen bonding. they are gases at room temp
ice consists of water molecules in the
hexagonal arrangement
the empty spaces between molecules in this pattern account for the relatively
low density of ice
as ice is heated, the increased energy of the molecules causes them to
move and vibrate more vigorously
when the melting pt is reached, the energy of the molecules is so great that the
rigid open structure of the ice crystals breaks down, and ice turns into liquid water
hydrogen bonds between molecules of liquid water at 0 degrees celsius are …. and more …. than those between molecules of ice at the
fewer; disordered; same temperature
because the rigid open structure of ice has broken down, water molecules can
crowd closer together
liquid water is
denser than ice
as the liquid water is warmed from 0 degrees celsius, the water molecules
crowd still closer together
water molecules are as tightly packed as possible at
3.98 degrees celsius
at temperatures above 3.98 degrees celsius, the increasing kinetic energy of the water molecules causes them to
overcome molecular attractions
the molecules move farther apart as the temperature continues to
rise
as the temperature approaches the boiling point, groups of liquid water molecules absorb enough energy to
break up into separate molecules
because of hydrogen bonding between water molecules, a high kinetic energy is needed, causing water’s boiling point to be
relatively high (100 degrees celsius) compared to other liquids that have similar molar masses
at room temperature, pure liquid water is
transparent, odorless, tasteless, and almost colorless
any observable odor or tase is caused by
impurities, such as dissolved minerals, liquids, or gases
water freezes and ice melts at
0 degrees celsius at a pressure of 1 atm
molar enthalpy of fusion of ice is
6.009 kJ/mol
the molar enthalpy of fusion of ice is relatively larged compared with the molar enthalpy of fusion of
other solids
water has the unusual property of …. in volume as it freezes, because its molecules form an..
expanding; open rigid structure
ice at 0 degrees celsius has a density of only about …. wile liquid water at 0 degrees celsius has a density of
.917 g/ cm3 ; .99984 g/ cm3
this lower density explains why ice floats in
liquid water
the insulating effect of floating ice is particularly important int he case of
large bodies of water
iv ice were more dense than liquid water, it would sink to the bottom of
lakes and ponds, where it would be less likely to melt completely
the water of such bodies of water in temperature climates would eventually
freeze solid, killing nearly all the living things in it
at 100 degrees celsius (boiling point at 1 atm) water’s molar enthalpy of vaporization is
40.79 kJ/ mol
both the boiling pt and the molar enthalpy of vaporization of water are quite high compared with those of
nonpolar substances of comparable molecular mass, such as methane
the values are high because of the strong hydrogen bonding that must be overcome for
boiling to occur
the high molar enthalpy of vaporization makes water useful for
household steam-heating systems
the steam (vaporized water) stores a great deal of
energy as heat
when steam condenses in radiators, great quantities of
energy are released
