Class 12 chemistry-I subject. Baord- Maharashtra. also used for Cet, jee, aipmt, exam.

65. Pex
V2
And the
Volume
change.

83. 2 3 4

88. Path dependence nature of work
• Work is not the property of the system.
• Not state funtion.
W = - P (V2-V1)
A
(V1)

93. q + W

109. 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

118. = qp

128. 1

159. IUPAC Guideline for writing
thermochemical equations

181. Bond dissociation enthalpy
Amount 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

201. 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 =
q
T
=
𝐽
𝐾
=
𝑐𝑎𝑙
𝐾
• 1 e.u. = 1 JK-1
• Entropy measure the disorder in the system.
• Higher the disorder more is entropy

202. 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 =
∆𝑯˚𝒇𝒖𝒔
𝑻
Solid to liquid
• ∆S =
∆𝑯˚𝒗𝒂𝒑
𝑻
liquid to gas
• ∆S =
∆𝑯˚𝒔𝒖𝒃
𝑻
solid to gas

203. 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.

223. 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.

224. • ∆S = qrev/ T =
∆𝑯
𝑻
• For infinitesimal change, dS =
𝒅𝑯
𝑻
.
• If Cp = molar heat capacity at const P, then
• Cp =
𝒅𝑯
𝒅𝑻
or dH = Cp.dT
• dS =
𝑪𝒑.𝒅𝑻
𝑻
• If temperature change from T1 to T2, then the
entropy change ∆S will be.
• ∆S =
𝑪𝒑.𝒅𝑻
𝑻
• ∆S = 2.303 Cp log
𝑻𝟐
𝑻𝟏
Entropy change at different T and
constant pressure

227. Entropy change at different T and
constant pressure