WATER, TAKEN IN MODERATION, CANNOT HURT
ANYBODY.
- Mark Twain -
CYCLES ARE COMMON IN NATURE.
WE EVEN SAW THEM IN ASTRONOMY. STARS
HAVE A FINITE LIFETIME. THEY ARE BORN IN
NEBULAS, THEY PRODUCE ENERGY, USE UP
THEIR FUEL, AND DIE IN GIGANTIC
EXPLOSIONS CALLED SUPER NOVA.
THE DUST AND GAS IS SCATTERED IN SPACE
AND EVENTUALLY FORMS INTO NEBULA, AND
THE CYCLE BEGINS AGAIN.
ON THE SURFACE OF THE EARTH, WE HAVE THE ROCK
CYCLE.
PLATE TECTONICS USE ENERGY FROM THE INTERIOR OF THE
EARTH TO BUILD UP CONTINENTS AND MOUNTAINS.
WEATHERING AND EROSION WEAR THE ROCK DOWN AND
CREATE NEW ROCK THROUGH SEDIMENTATION.
ROCKS ARE SUBDUCTED AS PLATES COLLIDE.
THEY CAN BE MELTED AND COOLED TO MAKE
IGNEOUS ROCK.
OR, THEY CAN BE RECRYSTALLIZED THROUGH
HEAT AND PRESSURE TO MAKE METAMORPHIC
ROCK.
THE WATER CYCLE IS PART OF THIS BATTLE OF FORCES THAT
SHAPES THE SURFACE OF THE EARTH.
THE SUN SUPPLIES THE ENERGY TO DRIVE THE WATER
CYCLE.
THERE ARE THREE WAYS WE CAN LOOK AT THE WATER
CYCLE.
- FIRST, WE COULD LOOK AT THE RESERVOIRS THAT
CONTAIN THE WATER IN THE WATER CYCLE
- SECOND, WE COULD LOOK AT THE RESIDENCE TIMES
FOR WATER IN THE RESERVOIRS
- THIRD, WE COULD LOOK AT THE PATHWAYS
BETWEEN THE RESERVOIRS – HOW THE WATER
MOVES BETWEEN THEM
97.5% OF ALL WATER ON EARTH IS SALT.
2.5% IS FRESH.
2.0% IS FROZEN (ICE CAPS OR GLACIERS)
0.592% IS GROUND WATER
0.014% IS RIVERS, LAKES, WATER VAPOR
REMEMBER, 70% OF EARTH’S SURFACE IS
COVERED WITH WATER – MOST OF IT SALT.
THAT SEEMS LIKE A VERY SMALL AMOUNT OF WATER AS
FRESH SURFACE WATER. HOWEVER, THE RESIDENCE TIME
FOR A MOLECULE OF WATER AS WATER VAPOR IS VERY
SHORT – ON AVERAGE ABOUT ONE DAY.
WATER IS CONTINUALLY MOVING IN THIS CYCLE.
THE RESIDENCE TIME OF A WATER MOLECULE AS
SURFACE FRESH WATER COULD BE MEASURED IN YEARS.
THE RESIDENCE TIME OF A WATER MOLECULE AS
GROUND WATER COULD BE MEASURED IN THOUSANDS
OF YEARS.
EVENTUALLY, ALL WATER FLOWS BACK TO THE OCEANS.
MOST OF THE WATER THAT WE HAVE ON EARTH HAS
BEEN HERE FOR AT LEAST 4 BILLION YEARS.
VERY LITTLE IS CREATED OR DESTROYED. IT IS SIMPLY
REUSED.
WATER IS A VERY UNUSUAL COMPOUND. IT IS A POLAR
MOLECULE, AND THIS GIVES IT SOME SPECIAL
PROPERTIES.
IN A POLAR MOLECULE, THE CHARGES ARE NOT
EQUALLY DISTRIBUTED, SO IT HAS A NEGATIVE END
AND A POSITIVE END.
SPECIAL PROPERTIES OF WATER:
1) IT HAS A HIGH MELTING POINT AND BOILING
POINT FOR ITS MASS
2) IT IS A GREAT SOLVENT
3) IT HAS A HIGH HEAT CAPACITY
4) IT HAS A HIGH HEAT OF FUSION AND HEAT
OF VAPORIZATION
5) IT HAS A HIGH SURFACE TENSIION
6) THE SOLID IS LESS DENSE THAN THE LIQUID
SINCE WATER IS A POLAR MOLECULE, IF YOU PUT A
BUNCH OF WATER MOLECULES TOGETHER, THE
POSITIVE ENDS OF SOME WILL BE ATTRACTED TO THE
NEGATIVE ENDS OF OTHERS.
THIS GIVES THE MOLECULES AN ADDITIONAL
“STICKEYNESS” THAT MANY SUBSTANCES DON’T HAVE.
Melting Point Boiling Point
Water, H2O
Methane, CH4
Oo C
100o C
-184o C
-162o C
WATER AND METHANE HAVE MOLECULAR MASSES THAT
ARE SIMILAR, BUT THEY HAVE VERY DIFFERENT MELTING
AND BOILING POINTS BECAUSE OF THE ADDITIONAL
STICKEYNESS.
HEAT CAPACITY IS THE AMOUNT OF HEAT REQUIRED TO
RAISE THE TEMPERATURE OF 1 GRAM OF A SUBSTANCE 1
oC.
WATER HAS A HEAT CAPACITY OF 1 CALORIE PER GRAM
PER DEGREE.
THIS MEANS THAT IT WOULD TAKE 100 CALORIES TO
RAISE THE TEMPERATURE OF 1 GRAM OF WATER FROM
0oC TO 100oC.
THIS HELPS PROVIDE THERMAL STABILITY TO OUR
BODIES, AS WE ARE ABOUT 2/3 WATER.
HEAT CAPACITY – 1 CALORIE PER GRAM PER DEGREE
HEAT OF FUSION – 80 CALORIES PER GRAM (HEAT TO
MELT 1 GRAM OF ICE)
HEAT OF VAPORIZATION – 540 CALORIES PER GRAM
(HEAT TO VAPORIZE 1 GRAM OF WATER TO WATER
VAPOR)
THE HIGH HEAT OF VAPORIZATION HELPS WHEN WE
COOL THE BODY THROUGH SWEATING IN THE SUMMER.
SOLID WATER IS LESS DENSE THAN LIQUID WATER.
THIS WOULD BE VERY IMPORTANT IF YOU WERE A FISH.
SURFACE TENSION IS THE ENERGY REQUIRED TO INCREASE
THE SURFACE AREA OF A LIQUID.
SURFACE TENSION IS DUE TO UNEQUAL FORCES AT THE
SURFACE OF WATER.
THERE ARE NO MOLECULES ABOVE THE SURFACE, SO ALL OF
THE FORCES ARE DIRECTED TO THE SIDES AND DOWN.
SURFACE TENSION IS WHY WATER DROPLETS ARE
SPHERICAL.
A SPHERE HAS THE HIGHEST VOLUME TO SURFACE
AREA RATIO OF ANY SOLID.
SURFACE TENSION IS ALSO WHY WATER SPIDERS CAN
WALK ON THE SURFACE OF WATER.
REVIEW OF THE SPECIAL PROPERTIES OF WATER:
1) HIGH MELTING POINT AND BOILING POINT FOR ITS
MOLECULAR MASS
2) HIGH HEAT CAPACITY
3) HIGH HEAT OF FUSION
4) HIGH HEAT OF VAPORIZTION
5) HIGH SURFACE TENSION
6) WATER EXPANDS WHEN IT FREEZES
7) GREAT SOLVENT