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