# Chapter 5 – Chemical Reactions

Document Sample

```					Chapter 5 – Chemical Reactions – Chem 11/Daniel
5.1 Intro
Chemistry study of matter and its changes.

Chem rxn definition

Chemical equation

Conservation of mass

5.2 Molecular Weight and Formula Weights
10. g/marble * 1000 marbles = 10,000 g = 10 kg
Count by weighing

Factor Label Method. Show how I can count 500 marbles by weighting.

Ionic vs molecular Cmp

H2O (molecule) versus NaCl (formula unit)

atomic weight = atomic mass =
.

1 amu = ? g _________________g

1 average H atom =__________ amu       1 averageO atom ___________ amu

1 H2O molecule has a molecular weight of

2 H atoms X _________ amu/H atoms = 2 X 1.008 =     2.016 amu

1 O atom X __________amu / O atom=1 X 15.999 = 16.00
=                 18.016 amu (? SF)

1 NaCl formula unit has a formula weight of 22.9898 amu
+ 35.4527 amu
= 58.4425 amu
formula weight more general term, can be used for formula units or covalent
compounds, molecular weight only used for molecules.

5.3 Our friend the mole
1 molecule or 1 FU not good for much

ammonia = NH3

molecular weight of NH3 = ____________________amu

~14 amu N / 3 amu H = ratio by mass of N to H needed

1 atom N has a mass of 14.0067 amu
large # N has a mass of 14.0067 g
Large # called a mole

Mole definition relative to 12C

Mass of 1 mole of C = 12.01 g
Mass of 1 mole of O =__________________

Mass of 1 mole of U = __________________

Molar mass definition

Avogadro’s # = 1 mole = 6.02 X 1023 12C has a mass of 12 grams
“         of O atoms has a mass of 15.9994 grams

“           of O2 molecules has a mass of ______________________

1 mole of O2 molecules has 2 mole of O atoms
Molar mass of O atoms 15.9994 g/mol
Molar mass of O2 molecules 31.9988 g/mol
molar mass of NaCl is 58.4425 g/mol

Take ammonia, NH3    ~17 g ammonia/mol, 1 mol N/3 mol H

I have 50.0 g of NH3 How many moles of NH3 do I have?

50.0 g NH3 X 1 mol NH3/ 17.03 g NH3 = ____________________

How many moles N and H do I have? NH3 tells you 1 mol N / 1 mol NH3 and 3
mol H/1mol NH3
2.94 mol NH3 X 1mol N/1mol NH3 = ________________ mol N

and 2.94 mol NH3 X 3 mol H/1 mol NH3 = ________________mol H

I have 100. moles of ammonia, what mass do I have?

________mol NH3 X _________g NH3 / mol NH3 = _____________g

How many ammonia molecules do you have?
100. mol X ( 6.02 X1023 molecules/ mol ) = 6.02 X 1025 NH3 molecules

What is molar mass (NH4)3 PO4

Molar mass Ferrocene (C5H5)2 Fe = (10XC) + (10XH) + Fe = 186.034 g/mol
5.4 Balancing equations:
Dalton explained conservation of mass by saying atoms not created or
destroyed.

Chemical change – reactants  products atoms rearranged
HgO              Hg + O2

2HgO → 2Hg + O2

p.137 How to Balance

1. Begin with elements that appear in only one reactant and one
product
2. Save free elements for last.
3. Change coefficients, not chemical formulas

Combustions reactions of organic compounds - Balance C,H,O
O in every substance, save for last
O2 element save for last

Catabolism – ca tab o lism

C6H12O6 + O2 →         CO2 + H2O

Initial amounts
C     6       →     1

H      12       →     2

O       6+2     →     2+1        Multiply by coefficients and save O for last to
balance.
Balance

N2 + O2 → N2O3           (dinitrogen trioxide)

N

O

Al + 3HCl       →     AlCl3 + H2 (Balancd H last)

Al

Cl

H

*******************************************************************************

N2 + 3H2 → 2 NH3

N

H

******************************************************************************
Co (NO3)2 + K3PO4 →Co3(PO4)2 + KNO3

Co2+

K+

NO3-

PO43-
5.5 Mass relationships in chemical rxn. Stoichiometry
N2   +   3H2   →     2 NH3

1 molecule + 3 H2 molecules → 2 ammonia molecules

1 dozen N2 + __________dozen H2 → _________dozen NH3

1 mol N2   + __________ mol H2 →____________mol NH3

I need 150. moles ammonia, how many moles of N2 and H2 needed

150. mol NH3 X 1 mol N2 / 2 mol NH3 = ____________ mol N2

150. mol NH3 X 3 mol H2 / 2 mol NH3 = ____________ mol H2

Pt Cl4 + 2 NH3  Pt Cl2 (NH3)2 + Cl2

I need to make 45 mol of cisplatin. How much platinum (IV) chloride and
ammonia are needed?
N2    +       3H2 →           2 NH3
28 g/mol      2 g / mol        17 g / mol

28 g +           6g             34 g

I need 100. g ammonia.
How many grams N2 and H2 needed?

1.   convert g NH3 into moles NH3
2.   convert mole NH3 into moles then grams N2
3.   convert mole NH3 into moles then grams H2

Limiting Reactant – Say I have 4 moles of N2 and 9 moles H2. How much NH3
can I make?

N2         +           3 H2             2 NH3

6 ammonia

8 ammonia

2 mol NH3
4 mol N2 x       1 mol N2          =       8 mol NH3 (if we have plenty of H2)

2 mol NH3
9 mol H2 x                             =    6 mol NH3 (if we have plenty of N2)
3 mol H2

Which reactant limits production (or makes less) of NH3? This is the limiting
reactant.
I need 500. mol of NH3 made. How many mol N2 and mol H2 are needed?

H is the limiting reactant

Gasoline + oxygen used to power your car. Which react limits how far you can
travel?

OH

Vitamin A

Rhodopsin                 N             Opsin
reacts to light, sends
nerve impulse to visual cortex

Lack of limiting reactant vitamin A leads to night blindness due to lack of
Rhodopsin.
5.6 Predicting Aqueous Reactions
Dissociation definition

H2O       Na+(aq) + Cl-(aq)
NaCl(s)
alakali
metal
compound
H         O
H
H   O               H
H20      Ag+ + NO-3
AgNO3(s)                                             Na+       Cl-

ions can react

NaCl (aq) + AgNO3 (aq)→ AgCl (s) + NaNO3 (aq)

Spectator Ions

Net Ionic Equation
p. 146 – 4 Reaction Types

Types of reactions:

Combination:         A + B → AB

C + O2 → CO2

Decomposition: AB → A + B

Single Replacement:         A + BX → B + AX

Double replacement:               AX + BY → BX + AY(s,g,molecule)

Combustion:                 S + O2 → SO2
5.7 Reduction and Oxidation – e- transfer reactions

0      0               2+    2-             Combustion
2 Mg + O     2           Mg      O
-
2 e /(Mg atom) transfer

0          +        -           2+       -        0   Single Replacement
Cu + 2 Ag NO3               Cu         (NO3 )2 + 2 Ag

Mg (s) + HCl (aq) → H2 (g)+ MgCl2 (aq)

Oxidation

Reduction

OILRIG –

Ranking electronegativity H < C < O. So oxygen has a stronger
attraction on e- than C, and H has a weaker attraction on e-.

So, Oxidation is also C gaining oxygen, or C losing H
Reduction is also C losing oxygen, or gaining H
Redox reaction of ethyl alcohol in the body
H
O
H        H                                      H
O
H      C   C

H         C        C       O                          H   C       C
O
H
H                                     H
H        H                                      H                                           H
Oxiation - Removal of 2 H                                  Addition of O

H

H           O
H           C       O    H
C

H                   OH
H                      OH

HO                      H
HO                         H
Reduction
H                   OH
H                      OH

H                   OH
H                      OH

CH2OH
CH2OH

d - glucose                                           d-sorbitol (sugar substitute for diabetics

Oxidizing agent (oxidant)

Reducing agent (reductant)
Fe + O2 → Fe2O3

Substance reduced___________________= oxidizing agent_______________

Substance oxidized __________________= reducing agent________________

Mg + 2 HCl →Mg Cl2 + H2

5.8 Heat of Reaction

exothermic.

endothermic

```
DOCUMENT INFO
Shared By:
Categories:
Stats:
 views: 85 posted: 2/22/2010 language: English pages: 13