Physical chemistryPREPARED BY:

NOR SYAFINAZ BINTI ABDUL GHANIMIC2A2

2010466248

Chapter 1

THERMOCHEMISTRY

Thermal energy is the energy associated with the random motion of atoms and molecules.

Heat is the transfer of thermal energy between two bodies that are different temperature.

Temperature is a measure of thermal energy.

Heat

Enthalpy of a system is the heat content of the system or the sum of the internal energy and the product of its pressure & volume.

Also known as heat content.

Enthalpy (H) is used to quantify the heat flow into and out of a system in a process that occurs at constant pressure

∆H˚=∑ H˚ᶠ(products)-∑H˚ᶠ(reactants)∆H : heat given off or absorbed during a reaction at

constant pressure.

ENTHALPY

Internal energy of reactant is greater than the product

Heat released to the surrounding

∆H is negative

exotherm

ic

Internal energy of product is greater than the reactant

Heat is absorbed from the surrounding

∆H is positive

endothermic

∆H<0 2H2(g) + O2(g)

energy heat

2H2O(l)

∆H>0 2Hg (l) + O2(g)

Energy heat

2HgO(s)

Heat/enthalpy of reaction

The enthalpy of combustion

• Energy released as heat when a compound undergoes complete combustion with oxygen under stated condition of temperature & pressure.

The enthalpy of neutralisation

• Heat released when one mole water is formed when an acid reacts with a base under stated condition or during the neutralisation of strong acid by an alkali.

• The value is always negative

The enthalpy of solution

• The heat change when one mole of substance or a certain amount of solute dissolve in a certain amount of solvent.

The enthalpy of formation

• The heat change when one mole of a compound is formed from its element s at stated temperature and pressure.

The enthalpy of reaction

• The enthalpy change in reaction when both reactantas and products are at their standard states at 298 K.

Calorimetry•Measurement of heat flow.

Calorimeter•Apparatus that measures heat flow.

Heat capacity•The amount of energy required to raise the temperature of an object.

Molar heat capacity•Heat capacity of 1 mol of a substance.

Specific heat capacity

•Heat capacity of 1g of a substance.

Calorimetry

Calorimetry

method

q = mc∆T

q = c∆T

qrxn= -(qwater +

qbomb)

∆H = qrxn/no. of

mole

For any chemical change made in several steps, the net ∆H is equal to the sum of the

∆H values of the separate steps

Hess’ law

Balance the equation(s).

Sketch a rough draft based on

∆H values.

Draw the overall chemical reaction

as an enthalpy diagram.

Draw a reaction representing the

intermediate step.

Check arrows.

complete balancing – all

levels must have same atoms

Add axes and ∆H values.

Steps in drawing enthalpy diagrams

Enthalpy cycle used to calculate lattice enthalpy of an ionic compound

Two different routes to form an ionic compound.

BORN-HABER CYCLE

The enthalpy change when one mole of an ionic solid is formed from its gaseous ions.

The values are always negative because of formation of ionic bond.

Lattice energy

Chapter 2CHEMICAL KINETICS

The change in the concentration of a reactant or a product with time (M/s)

A B reactant(-) product(+) rate of appearance = positive rate of dissapearance = negative

Reaction rate

Expresses the relationship of the rate of reaction to the rate constant and the concentrations of reactants raised to some powers.

aA+bB→ cC+dDRate = k [A]x [B]y

Order of reaction xth order in A yth order in B (x+y)th is the overall order

Rate law

ORDER RATE LAW CONCENTRATION- TIME EQUATION

HALF-LIFE

0 Rate=k [A]= [A]- kt .t1/2=[A]/2k

1 Rate=k[A] Ln[A]= ln[A]-kt

t1/2= ln2/k

2 rate=k[A]^2 1/[A]=1/[A] +kt

t1/2= 1/k[A]

Concentration of reactants – concentration of reactants increase, so does the likehood that reactant molecules will collide.

Temperature – at high temperature,reactants molecules have more kinetic energy,move faster and collide more often.

Catalyst – speed rxn by changing mechanism.

Activation energy – minimum amount of energy required for reaction.

Factors affecting reaction rates

k = A.e(-Ea/RT)

Ea = activation energy (J/mol)

R = gas constant (8.314 J/K.mol)T = absolute temperature

A = frequency factor

Arrhenius equation

At two temperature, T1 and T2

Ln k1/k2=Ea/R(1/T2-1/T1)

Alternate form of the Arrhenius Equation

The overall progress of a chemical reaction represented by a series of elementary steps.

The sequence of elementary steps lead to product formation is the reaction mechanism.

Reaction mechanisms

Rate laws and elementary steps

Molecularity Elementary reaction

Rate law

Unimolecular A product Rate = k[A]

Bimolecular A + A product Rate = k[A]2

Bimolecular A + B product Rate = k[A][B]

Termolecular A + A +A product Rate = k[A]3

Termolecular A + A + B product

Rate = k[A]2[B]

Termolecular A + B + C product

Rate = k[A][B][C]

Chapter 3CHEMICAL EQUILIBRIUM

•Reacting species are the same phase•i.e: N2O2(g) 2NO2(g)•K’c = [ NO2 ]2 / [ N2O2 ]

Homogenous equilibrium

•Reactants and product are in different phases•i.e: CaCo3 (s) CaO (s) + CO2 (g)•K’c = [CaO] /[CaCo3]•The concentration of solid and pure liquid are not included in the expression for the equilibrium contant.

Heterogenous

equilibrium

Kp = Kc (RT)∆n

R = room pressure = 0.0821∆n = moles of gaseous products-

moles og gaseous reactant

If an external stress is applied to a system at equilibrium,the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position

Le Chartelier’s principle

change Shift equilibrium Change equilibrium constant

Concentration yes no

Pressure Yes no

Volume Yes no

Temperature Yes yes

catalyst No no

Chapter 4IONIC EQUILIBRIUM

THEORIES TO EXPLAIN ACID AND BASES

ARRHENIUS THEORY

Acid=dissociate in water to

produce hydrogen atomBase=dissociat

e in water to produce

hydroxide ions.

BRONSTED-LOWRY THEORY

Acid= a proton donor

Base= a proton acceptor

LEWIS THEORY

Acid=electron pair acceptor

Base =electron pair donor

ᾱ = [H3O] / [acid]

ᾱ = [H3O] / [acid] x 100

Degree of dissociation

1.For strong acidpH=-log [H]

2.For weak acid[H]=√KaC[OH]=√KbC

3.pH of Buffer pH= pKa-log[acid/salt]

pOH=pKa-log[base/salt]pKa= -logKa

4. Kw = [H][OH] = Ka x Kb = 1 x 10-4

Formulae

Chapter 5PHASE EQUILIBRIUM

A homogeneous system Separated from other parts of system

by a dinstinct boundary 3 phase of state

solidliquid

gaseous

Phase, ‘p’

No boundary between subtances – hemogenous

i.e: g-g system : oxygen and nitrogen l-l system : water and ethanol s-s system : gemstone

One phase system

Two substance with a boundary separating them

i.e: l-l : water and oil l-g : water and water vapour s-g : ice and water vapour

s-l : ice and water

Two phase system

3 substance with boundaries separating each other

i.e: s-l-g : ice, water and water vapour system

Three phase system

The least number of independently variable constituents which must be specified so that composition of each and every phase is described.

Component, ‘c’

The smallest number of independent variables of components (temperature, pressure, concentration) which must be specified to define completely the remaining variables of the system

Degree of freedom, ‘f’

F = C – P + 2

More components, more degree of freedomMore phases involved, less degree of freedom

Phase rule

One component system

Water and carbon dioxide

pressure, atm

solid liquid

0.006 gas

0.01 temperature,(0c)

Phase diagram of water

Phase diagram of carbon dioxide

pressure, atm

temperature, (0c)

solid liquid

gas

5.1

-57

Two component system

Two completely immisible solids (l-s)

Eutectic mixture – a mixture of 2 or more subtance with melting point lower than any other mixture of the same subtance

Eutectic system – a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other temperature

Non-ideal solutionDeviation from raoult’s law

Negative deviation

•Vapour-composition diagram of solution have minimum point•Boiling-composition diagram has maximum point

Positive deviation

•Vapour-composition diagram of solution have maximum point•Boiling-composition diagram has minimum point

Type of deviation

Partition coefficient= the ratio between the concentration of the

solute in the two solvents is, experimentally

constant.

PARTITION COEFFICIENT

Kc= [solute in upper layer]/[solute in the lower layer]

Kc= X/volume of ether mass of substance-X/volume of

water

formula