Chemical thermodynamic and Energetic

P.E transform into K.E.

Macroscopic Science

Deals with large no. of atom or molecule not individual atom or molecule.

e

Exchange Neither matter

nor energyIs called isolated system.

System which contain more

then one phase is called

heterogeneous system.

Const T

All reaction carried out in lab are at constant P.

Since the temperature

change, internal energy also change.

But T does change in

the system.

Against an External Pex

Pex

V2

And the Volume change.

2 3 4

The process take place in infinite

steps.

Path dependence nature of work

• Work is not the property of the system.• Not state funtion.W = - P (V2-V1)

A(V1) B

(V2)

W1 Expand Path1

W2 Pex2

W3 exapnsion reversibly 3

q + W

It indicate small change.

The process in which T of the system

remain Constant.

a process in which heat is not allowed

enter or leave the system.

A process in which

pressure remain

constant.

A process in which

Volume remain

constant.

Concept of Heat

• Another way of exchanging energy system and surrounding.• Not property of system. Not state

funtion.• Heat exchange only possible by path.• Heat is path dependence.• Eg. Rod heat transfer

qp

Heat content of the system at constant

pressure.

= qp

In general enthalpy change is given by

1

The component present in small quantity.

The component present in Large quantity.

IUPAC Guideline for writing thermochemical equations

Again Supply energy

Each step supply energy

Bond dissociation enthalpyAmount of energy require to break 1 mole of of a particular bond of a particular polyatomic gaseous molecules forming free gaseous atoms and radicals at constant temperature and pressure.STEP 1: CH4(g) → CH3(g) + H(g) ; Δbond H° = +427 KJmol-1

STEP 2: CH3(g) → CH2(g) + H(g) ; Δbond H° = +439 KJmol-1

STEP 3: CH2(g) → CH(g) + H(g) ; Δbond H° = +452 KJmol-1

STEP 4: CH(g) → C(g) + H(g) ; Δbond H° = +347 KJmol-1

Average bond enthalpy ΔC-HH° = ¼ (ΔaH°) = ¼ (1665 KJmol-1) = 416 KJmol-1

Entropy• Entropy change(∆S) of a system in a process

which is equal to the amount of heat transferred in a reversible manner(qrev) divided by the absolute temperature(T), at which the heat is absorbed.

• ∆S = = • 1 e.u. = 1 JK-1

• Entropy measure the disorder in the system.• Higher the disorder more is entropy

Entropy change for a phase change

• Phase change physical state of matter.• During phase change, both the phases

exist at equilibrium and temperature remain constant.• ∆S = Solid to liquid• ∆S = liquid to gas• ∆S = solid to gas

Different process accompanying entropy change

• Solid to liquid to gas entropy increases.• Solid or liquid dissolve in a solvent, entropy of the

substance increase.• When gas dissolve in solvent, entropy decreases.• When the gas mix, entropy increase.• Increase molecular complexity result in the increase in

entropy.• Spontaneous process, expansion of gas, disorder of

the system increase entropy.• Eg. When the Tr leave classroom entropy increase.

Unit- SI is J or kJCGS is cal or kcal.

Important of 3rd law of thermodynamic

• It gives the starting place from which to measure entropy.

• Entropy of a substance determine at any temperature higher then 0K at any state.

• Stand molar entropy (S˚) can be measure at 25˚C and 1 atm.

• Spontaneity of the reaction and ∆S˚ can be calculated.

• ∆S = qrev/ T = • For infinitesimal change, dS = .• If Cp = molar heat capacity at const P, then• Cp = or dH = Cp.dT• dS = • If temperature change from T1 to T2, then the

entropy change ∆S will be.• ∆S = • ∆S = 2.303 Cp log

Entropy change at different T and constant pressure

Entropy change at different T and constant pressure