Chemical Thermodynamics Notes PDF

# ABHISHEK SIR CHEMISTRY ## CHEMICAL THERMODYNAMICS **System:** A part of the universe under thermodynamic investigation. ### TYPES OF SYSTEM * **Open system:** exchanges both energy & matter * **CLOSED SYSTEM:** exchanges only energy & not matter. * **ISOLATED SYSTEM:** exchanges not allow exch...

# ABHISHEK SIR CHEMISTRY ## CHEMICAL THERMODYNAMICS **System:** A part of the universe under thermodynamic investigation. ### TYPES OF SYSTEM * **Open system:** exchanges both energy & matter * **CLOSED SYSTEM:** exchanges only energy & not matter. * **ISOLATED SYSTEM:** exchanges not allow exchange of either energy or matter ### EXTENSIVE Property: A property which depends on amount of matter * eg: Mass, Volume, internal energy, heat capacity, no. of moles. ### INTENSIVE Property: A property which is independent of amt of matter * eg: Pressure, Temp. ### State Function: Property which depends on state of the system & independent of path. * eg: density, enthalpy. ### Path function: Property which depends on path. * eg: klork, heat. ## Thermodynamic Equilibrium: A system is said to be in the thermodynamic equilibrium when it's state functions do not vary with time. Thermodynamics considered here is limited to equilibrium states. ### PROCESS & Its TYPES 1. **ISOTHERMAL PROCESS** It is the process in which temperature of the system remains constant. ΔT = 0 2. **ISOBARIC PROCESS.** It is the process in which pressure remains constant during the transformation. ΔP = 0 3. **ISOCHORIC PROCESS:** It is the process during which the volume of the system remains constant during the transformation. ΔV = 0 4. **ADIABATIC PROCESS** The process in which there is no exchange of heat between the system and surrounding is Adiabatic process. Q = 0 ## # Nature of klork: P = f /A : PV = f x V/A = f x d3/d2 : W = fd ## # SIGN CONVENTIONS * **Work done on the system:** +W * **Work done by the system:** -W * **Heat absorbed:** +Q * **Heat released:** -Q ## # Expression for PV Work f = -Pext x A - (1) W=Fxd .: W = -Pext x Axd... from (1) AV = Axod - (2) .: W = -Pext x ΔV .... from(2) ∴ W = -Pext (V2-V1) If V=0 W = -Pext x ΔV W = 0 ## # Concept of Maximum Work ΔP = P-Pext Pext = P-ΔP W = - Pext ΔV W = -(P-ΔP) ΔV ## # Expression for Maximum klork: | Step 1 | Step 2 | Step 3 | continued | | :------------ | :------------- | :------------- | :---------- | | Gas | Gas | gas | gas | | dv | dv↑ | dv↑ | | | | | | | dw = -Pext dv P-Pext = dp .: P-dp = Pext - (1) dw = -(P-dp). dv .... from (1) dw = - P. dv + dp. dv dw = - P. dv By integrating We get, final ∫dw = -∫ P.dv initiat PV=nRT Wmax = -∫ P.dv = -∫ dRT/V. dv V1 Wmax = -nRT∫ dv/V V1 W2 Wmax = -nRT ln (V/V1) Wmax = -nRT ln (V2-V1)/V1 Wmax = -nRT ln V2/V1 Wmax = -2.303 *nRT log V2/V1 Also P1V1 = P2V2 P2/ P1 = V2/V1 Wmax = -2.303 *nRT log P1/P2 ## # Internal Energy: It is made up of kinetic & potential energies of individual particles of the system ΔU = U2-U1 ## # FIRST LAW OF THERMODYNAMICS: ΔU = Q+W ## # St law of Thermodynamics for Various Processes 1. **Isothermal Process:** Temp is constant : ΔU = 0 0 = Q + W or W=-Q 2. **Adiabatic Process** Φ=0 -ΔV=-W 3. **Isochoric Process** W= - Pext ΔV ΔU = Q-Pext ΔV - ΔU = Qv 4. **Isobaric Process** ΔV≠0 Qp = AU + Pext ΔV ## # Enthalpy: Enthalpy of a system is the sum of internal energy of a system & the energy is equivalent to PV work. H = U + PV - (1) ΔH = H2-H1 - H1 = U1+P1V1 - (3) H2 = U2 + P2V2 - (4) Substituting eqn (3) & (4) in (2) ΔH = U2+P2V2-U1+P1V1 = (U2-U1) + (P2V2-P1V1) -ΔH = ΔU+PΔV Qp = ΔU+PΔV ΔΗ=Qp ## # Relationship btn ΔΗ & Δυ ΔH = ΔU + PΔV ΔH = ΔU+P(V2-V1) ΔH = ΔU + PV2-PV1 But PV = nRT PV2 = n2RT .: ΔH = ΔU+ (n2RT-n1RT) ΔH = ΔU + (n2-n1) RT "ΔH = ΔH + Δng RT ## # klork done in chemical Reactn: W=-Pext ΔV = -PΔV = -P(V2-V1) W = -PV2 + PV1 By Ideal gas eqn, PV1=n1RT PV2 = n2RT W1 = -n2RT+n1RT = -(n2-n1) RT W = - ΔngrT ## # BOND ENTHALPY: The enthalpy change required to break particular covalent bond in one mole of gaseous molecule to produce gaseous atoms /radicals. ## # HESS LAW: Overall enthalpy change for the reaction is equal to the sum of enthalpy changes of individual steps in the reaction. * 2H2 + N2 → N2H4 * N2H4 + H2 → 2NH3 * 3H2 +N2 → 2NH3 ## # Entropy: The disorder of randomness is measured by entropy Enthropy is a measure of molecular disorder or randomness. ## # 2nd Law of Thermodynamics: Total entropy of a system and it's surrounding increases in a spontaneous process. AS total = AS sys + ASsurr> 0 * **i** AS total > 0 → Spontaneous * **ii** AS total < 0 → Nonspontaneous. * **iii** AS total = 0 → At equilibrium. ## # Gibbs Energy: Gibbs energy is defined as G=H-TS Change in Gibbs energy ΔG = ΔH-TAS * **Relation 6th ΔG & ΔStotal** ΔStotal = AS sys + Assurr - (1) But ΔStotal = AS + AS surr - ASSurr = ΔH/T - (2) .: ΔStotal = AS - ΔH/T .- from 2 .. TΔStotal = ΔH-TAS ΔG = -TAS total ## # Gibbs function & equilibrium constant: AG= AG°+ RTen Q Consider a A+bB→CC+dD ΔG = ΔG° + R T ln QC or = ΔG°+RTen [C]c [D]d / [A]a[B]b ΔG = AG° + R T en Qp = AG° + RTen PCx PD^d / PA^a PB^b At Equilibrium, AG°=0 Qc = Kc Qp = Kp 0 = AG° + RTlnge & 0 = AG° + R.T Inkp or AG° = -RT In Kc & AG° = -RT Inkp .: AG°= -2.303RTlogo Kc & AG°=-2-303 RTlogiokp