Energetics

Exothermic:
-Enthalpy of Products < Enthalpy of Reactants
-#H is negative
-Heat is being evolved into the surroundings
-A rise in temperature

Endothermic:
VICE VERSA!

Standard Enthalpy Change of Reaction
It is the energy change when molar quantities of reactants in the stated equation react together under standard conditions

>can be +ve or -ve
>Amount of reactants / products is halved, enthalpy also halved.

Standard Enthalpy Change of Formation
It is the energy change when one mole of compound is formed from its constituent elements under standard conditions

>#Hf of an element = O

Standard Enthalpy Change of Combustion
It is the energy change when one mole of compound is completely burnt in oxygen under standard conditions

>#Hc = -ve
>Excess O2 needed to ensure complete combustion
>determined by use of bomb calorimeter

Standard Enthalpy Change of Neutralisation
It is the enthalpy change when one mole od water is formed during the neutralisation of an acid and an alkali under standard conditions

>-57kJ/mol = involving STRONG acids and alkalis which are completely dissociated in aq.
>values lesser than -57kJ/mol (eg. -55kJ/mol): weak acids and alkalis only dissociated partially thus part of enthalpy evolved is used to dissociate them completely before neutralisaton occurs.

Standard Enthalpy Change of Atomisation
It is the energy change when one mole of gaseous atoms is formed from its element under standard conditions

>always +ve, endothermic, energy is needed to break al the bonds and seperate atoms

Standard Bond Dissociation Enthalpy, Bond Energy
It is the energy change to break one more of convalent bonds between 2 atoms in the gaseous states under standard conditions

>always +ve, endothermic
>reverse process of bond formation, -#Hf = +#Hdiss
>#Hatm = 1/2#Hdiss

First Ionisation Energy, 1st I.E
It is the energy change when one mole of electrons is being removed from one mole of gaseous atoms to form one mole of singly-charged cations

>always +ve, endothermic, energy needed to break attraction btwn nuclues and valance e.

First Electron Affinity, 1st E.A
It is the energy change when one mole of electrons is being added to one mole of gaseous atoms to form one mole of singly-charged anions.

>1st E.A = negative, evolves energy since a bond is formed
>2nd and .... = positive,, energy needed to overcome repulsive force btwn incoming e and -vely charged ion

Standard lattice Enthalpy, L.E
it is the enthalpy change when one mole of an ionic compound is formed from its constituent gaseous ins at standard conditions

>always -ve, exothermic

Standard Enthalpy Change of Hydration
It is the enthalpy change when one mole of gaseous ions is surrounded by water molecules, forming a solution at infinite dilution under standard conditions

>ion-dipole interaction
>always -ve, exothermic
>small, highly charged ions undergo hydration MOST easily
>total #Hhyd of a salt = #Hhyd(cation) +#Hhyd(anion)

Standard Enthalpy Change of Solution
It is the enthalpy change when one mole of substance is dissolved by solvent (usually H2O) such that further dilution produces no more heat change under standard conditions.

>can be +ve, -ve
>compounds with small endothermic value will absorb energy from surroundings to dissolve --> register drop in temperature
>more exothermic the #Hsol, the more soluble

Heat lost by reaction = heat gained by solution
Q = mc#T
#H = (heat evolved or absorbed) / (amt of substance)

Specific heat capacity,c, is the heat energy needed to raise the temperature of a substance of unit mass by 1K : kJ/kg/K

#Hrxn = sum of #Hc of R - sum of #Hc of P
#Hrxn = sum of #Hf of P - sum of #Hf of R
#Hrxn = sum of energies of bond BROKEN + sum of energies of bond FORMED

#Hsol = -L.E + #Hhyd

HESS' LAW
BORN HABER CYCLE

Entropy
S is a measure of the order of a system
-When a system is more disordered / more random, S increases, #S>0 (when the final state of system is of greater probability)
-#S = Sfinal - Sinitial (J/K/mol)

Change in volume of gases
In larger volume of space, there are more ways to arrange the gas particles in the system, hence S increases.

Change in phase
Sgas >> Sliquid > Ssolid
-During melting and boiling, there is an increase in disorder in the system since there're more ways to arrange the particles in system, hence S increases.
-During boiling, increase is S from liquid to gas phase is greater than increase S from solid to liquid because increase in volume from liquid to gas phase is greater than increase in volume from solid to liquid phase.

Change in no. of particles (esp gaseous system)
-Look at equation, if there is an increase in total no. of molecules (2mol--> 3mol), it will lead to increase in no. of ways to arrange the molecules in system, hence S increases.

Mixing of particles
-When a gas expands, particles will occupy entire container.
-When gases mix, each gas will expand to occupy entire container, this higher state of disorder, hence there are more ways to arrange the particles in system, hence S increaes.

Liquids
-Mixing od liquids with SIMILAR POLARITIES results in more ways to arrange the particles in system, hence S increases

Dissolving solids
-When an IONIC solid dissolves in a solvent (eg water), overall enthalpy change of system is contributed by entropy changed involved for interactions btwn solute and solvent particles.
-Entropy of dissolved ionic solid is usually higher than entropy of pur ionic solid as the ions experience a large increase n disorder as they break away from ionic lattice, hence increase in S.
-When formed ion-dipole interaction, water molecules become more ordered around ions, leading to decrease in disorder and hence decrease in entropy
-Overall entropy change depends on magnitudes of indiv entropy contributions

Change in Temperature
-temperature od system is proportional to energy possessed by particles in system (in quanta).
-total energy of system is not evenly distributed among particles
-higher temperature, more energy the system possesses which implies more ways to distribute the energy among particles, hence S increases.

Gibbs Free Energy Change, #G
-Under standard conditions, 298K, 101kPa
- #G = #H -T#S

-Free energy is the maximum useful work that can be produced by chemicaal reaction (with minimum heat produced)

-#G <0 : energetically feasible, reaction sponstaneous
-#G>0 : vice versa
-#G = 0: Equilibrium, no net change.
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