CHEMISTRY 161

Revision Chapters 4-6

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4. CHEMICAL REACTIONS

4.1. properties of solutions

4.2. reactions in solutions

a) precipitation reactions

b) acid-base reactions (proton transfer)

c) redox reactions (electron transfer)

non-electrolyte weak electrolyte strong electrolyte

methanol

sugar

ethanol

water

dark bright

ionic compounds

NaOH

HCl

H2SO4

CH3COOH

HCOOH

HF

medium

DISSOCIATION

‘breaking apart’

NaCl (s) → Na+ (aq) + Cl- (aq)

NaOH (s) → Na+ (aq) + OH- (aq)

HCl (g) → H+ (aq) + Cl- (aq)

strong electrolytes are fully dissociated

weak electrolyte

CH3COOH(aq) + H2O(l) H3O+(aq) + CH3COO-(aq)

NH3(aq) + H2O(l) NH4+ + OH-

strong electrolyte

HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq)

HNO3(aq) + H2O(l) → H3O+(aq) + NO3-(aq)

monoprotic acids

4.2.1. insoluble compounds

1.M+ compounds (M = H, Li, Na, K, Rb, Cs, NH4)

2. A- compounds (A = NO3, HCO3, ClO3, Cl, Br, I)(AgX, PbX2)

3. SO42-

(Ag, Ca, Sr, Ba, Hg, Pb)

4. CO32-, PO4

3-, CrO42-, S2-

(exception: M+)

4.2.2. ACID-BASE REACTION

acid + base → salt + water

(neutralization reaction)

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

molecular equation – ionic equation – spectator ions

4.2.3. OXIDATION NUMBER

ionic compounds ↔ molecular compounds

NaCl HF, H2

Na+Cl- ?electrons are fully transferred covalent bond

‘oxidation number’

charges an atom would have if electrons are transferred completely

TYPES OF REDOX REACTIONS

1.combination reactions

A + B → C

2. decomposition reactions

C → A + B

3. displacement reactions

A + BC → AC + B

4. disproportionation reactions

[p] = Nm-2 = kg m-1 s-2 = Pa

SI units

5. GASES

p × V = n × R × T

1. ideal gas equation

R = 8.314 J / mol / K

Vm = 22.4 l

2. molar volume

3. Kinetic Molecular Theory of Gases

4. Distribution of Molecular Speeds

Ekin = ½ M u2 = 3/2 R T

5. Real Gas Law

(p + (a n2 / V2) ) (V – n b) = n R T

Enthalpy of Reaction

heat released or absorbed by the system at a constant pressure

H = HH = Hproductsproducts - H - HreactantsreactantsH = HH = Hproductsproducts - H - Hreactantsreactants

Hfinal > Hinitial : H > 0 ENDOTHERMICHfinal > Hinitial : H > 0 ENDOTHERMIC

Hfinal < Hinitial : H < 0 EXOTHERMICHfinal < Hinitial : H < 0 EXOTHERMIC

6. THERMOCHEMISTRY

measurement of heat changes

HHmm = = ΔΔQQmm = = ccmpmp ΔΔTT HHmm = = ΔΔQQmm = = ccmpmp ΔΔTT

ccmpmp(H(H22O) = 75.3 J molO) = 75.3 J mol-1-1 K K-1-1ccmpmp(H(H22O) = 75.3 J molO) = 75.3 J mol-1-1 K K-1-1

H = H = ΔΔQ = (Q = (ccmpmp × n + c × n + ccupcup) ) ΔΔTT H = H = ΔΔQ = (Q = (ccmpmp × n + c × n + ccupcup) ) ΔΔTT

Standard Enthalpy of Formation

HHffOOHHff

OO

heat change when 1 mole of a compound is formed from its elements at a pressure of 1 atm

(T = 298 K)

HHffO O (element) = 0 kJ/mol(element) = 0 kJ/molHHff

O O (element) = 0 kJ/mol(element) = 0 kJ/mol

HHffO O (graphite) = 0 kJ/mol(graphite) = 0 kJ/molHHff

O O (graphite) = 0 kJ/mol(graphite) = 0 kJ/mol HHffO O (diamond) = 1.9 kJ/mol(diamond) = 1.9 kJ/molHHff

O O (diamond) = 1.9 kJ/mol(diamond) = 1.9 kJ/mol

EN

TH

AL

PY

, H

HHreactantsreactantsHHreactantsreactants

HHproductsproductsHHproductsproducts

C(s, graphite) + O2(g)

CO2(g)

Hf0 = - 393.51 kJ mol-1

0

-393.51

C(s, graphite) + O2(g) CO2(g) Hf0 = - 393.51 kJ mol-1

Standard Enthalpy of Formation

C(s, graphite) + 2H2(g) CH4(g) Hf0 = - 74.81 kJ mol-1

½ N2(g) + 3/2 H2(g) NH3(g) Hf0 = - 46.11 kJ mol-1

(1/2) N2(g) + (1/2) O2(g) NO(g) Hf0 = + 33.18 kJ mol-1

HHOOrxn rxn = = ΣΣnnΔΔHHff

00(prod) – (prod) – ΣΣmmΔΔHHff00(react)(react) HHOO

rxn rxn = = ΣΣnnΔΔHHff00(prod) – (prod) – ΣΣmmΔΔHHff

00(react)(react)

Standard Enthalpy of Reaction

CaO(s) + CO2(g) → CaCO3(s)

-635.6 -393.5 -1206.9 [kJ/mol]

HHOOrxn rxn = -177.8 kJ/mol= -177.8 kJ/molHHOO

rxn rxn = -177.8 kJ/mol= -177.8 kJ/mol

1 atm = 760 mm Hg = 760 torr = 103,325 Pa

R = 8.314 J / mol / K

cmp(H2O) = 75.3 J / mol / K

p V = n R T

HHOOrxn rxn = = ΣΣnnΔΔHHff

00(prod) – (prod) – ΣΣmmΔΔHHff00(react)(react) HHOO

rxn rxn = = ΣΣnnΔΔHHff00(prod) – (prod) – ΣΣmmΔΔHHff

00(react)(react)

Ekin = ½ M u2 = 3/2 R T

ΔΔQ = (Q = (ccmpmp × n + c × n + ccupcup) ) ΔΔTT ΔΔQ = (Q = (ccmpmp × n + c × n + ccupcup) ) ΔΔTT

Come in Time!Do not forget your calculator!