Chapter 5

THE WONDER OF WATER

Chap Overview

1. Use patters

2. Properties of

3. sources of

4. treatment of

5. ownership of

Properties - H2O is "suprising stuff"

"Universal" solvent

relatively hi BP&FP

high specific heat

Unusual Properties

Liquid @ RT & at. press (stp) N2, O2,C2

look @MM of H2O compared to these

#

Molecular Stucture & Physical Props

OH bond is covalent ---> e- shared but, unequal sharing look @ electronegitivity (table 5.5 p156)

relatice ability of atom to attract e- to itself

 

Polar Covalent Bond

     

 

H 2.1

So what happens when 2H2O molecules approach one another?

# How much E do you use taking a five minute shower?

1. Amt. of H20 (mass)

2. Temp. Change of H2O (Change in Temp.)

3. How much heat is needed to change eash gram of H2O?

So heat absorbed (q) =m x change in temp x S.H

If shower uses 19L/min

Homeostatis ---> 98.60F

Change of state 80cal/g

Solid ---> liqiud Heat of fusion What is it./mole?

-expands upon freezing

chemical formula ---> compostion

H2O How do we know?

electrolysis - the elctrical decomposition of a compound into its constiuent elements

cathode - electrode connect to (+) ---> O2 (g)

ratio --> 2:1 ---> H20

E+2H2O(e) ---> 2H2(g) +O2(g)

2H2 + O2 ---> 2H2O + E

#

Hydrogen Bonding

Intermolecular bond betwee molecule

*that is not as strong as an intramolecule

Props of H2O explained by H bonding

-High BP (1000C)

-High heat of vaporization (540 cal/g)

w/o H-bonding H2O would boil @ -750C

- expands upon freezing (fig 5.5)

-H2O is a highly associated liqiud

WATER AND ENERGY
High capacity to absorb hear

absorbed in oceans and clouds

During evaporation

realeased during condensation

in rain, sleet, snow

We cannot model the specifiecs of the system

Water vs ground (rocks, soil, etc)

Effects on climate and weather

Speicific Heat - quantity of hear energy required to raise 10C

H2) ---> 1 cal/g 0C = 4.184 J/g0C

#

80 Cal/g - Heat of Fusion

1440 cal + H20 (s) 0oC ---> H2O (L) @ 0oC

NO CHANGE IN TEMPERATURE

EQUILIBRIUM - 6 ICE CUBES IN A CUP

6 ICE CUBES IN A BUCKET

Liquid to gas - heat of vaporization

540 cal/g

9720cal + H2O(l) @ 100oC ---> H2O(g) @100oC

Why is this almost 7x greater than H.O.F

Intet mol. F b/w liquid and gas state

Much stronger than solied and liquid

#H20(l) has one of the highest sp. hear

It therefore makes a freat coolant

1. Human body

2. Industry

3. Power Plants

4. Cars (?)

Benzene C6H6 - .406 cal/goC

Why is water specific heart so high?

1. Structure

a. H bonding

b. resulting degree of order

REM - temp. is a measure of molec. motion

in crease in motion...increase in temp.

If mol. are strongly attached to each other, increase in energy to overcome Intermol. Forces H

H bonding is strong so E is high

#

Water as a solvent

Solvent - the component present in the largest concentration

Solute - component that dissolves in a solvent

Solution - homogenous Misture @ the atomic, molecular, and /or ionic level consisting of a solvent and a solute

Electrolyte - a solute that is capavle of conducting electricity

Solubility(?)

Ionic Compounds and Their solutions

NaCl - bonded by opposite charge

ions attracted to each other

(ionic bond) ---> Ionic compound

Na+ - cation

Cl- - anion

WHY DO CERTAIN ATOMS GAIN OR LOOSE AND ELECTRON?

Na has one e- in the outer orbital

- has strong tendency to lose it so it becomes Na+ ion this is

OXIDATION - a process where you loose an e-

CL has 7e- in outer orbital

has a strong tendency to aquire and e-

it becomes Cl- ion this is

REDUCTION - a process where you gain e-

SO...

2Na(s) + Cl2(g) -->2NaCl(o) + E

b/c NaCl conducts electricity this indicates e- transfer(Ionic bonding) not shared e-(covalent bonding)