Thermodynamics Chapter 6 PDF

 CHAPTER 6 Thermodynamics Thermodynamic Terms Processes System: Part of universe under investigation....

 CHAPTER 6 Thermodynamics Thermodynamic Terms Processes System: Part of universe under investigation. Isothermal Isochoric Isobaric Adiabatic Cyclic Surroundings: Rest part of universe except system. Boundary: Divide system and surroundings. T = const. V = const. P = const. No heat Initial and exchange final state System dq = 0 of system are same Open Closed Isolated Energy and matter Only energy can Neither energy nor can exchange exchange matter can exchange Reversible process Irreversible process State function Path function ™ Slow process ™ Fast process Properties for which change depends Change depends on path only on initial and final state of the or process. ™ At any time, system ™ Equilibrium between system and not on the process or path. e.g. work, heat system and surrounding e.g. U, H, S, G, etc. and surrounding are in only at initial and final equilibrium. stages. Thermodynamic Properties ™ Psys = Psurr ± dP ™ Psys = Psurr ± DP Extensive Intensive Heat (q) Properties which are dependent Properties which are independent Energy exchange due to temperature difference: on amount of matter (size and of amount of matter (size and mass) present in system mass) present in system. q = CDT, q = nCmDT, Molar volume Volume Density q = msDT Number of moles Refractive index Mass Surface tension C = Heat capacity Free Energy (G) Viscosity Entropy (S) Free energy per mole Enthalpy (H) Specific heat Cm = Molar heat capacity Internal energy (E and U) Pressure Heat capacity Temperature s = Specific heat capacity Boiling point, freezing point etc. m = Mass of substance General values of CV and CP for an ideal gas can be taken as follows. CV CP g Atomicity ntr nRot nVib Excl. Vib Incl. Vib Excl. Vib Incl. Vib Excl. Vib Incl. Vib 3 3 5 5 5 5 Mono 3 0 0 R R R R 2 2 2 2 3 3 5 7 7 9 7 9 Di 3 2 1 R R R R 2 2 2 2 5 7 5 13 7 15 7 15 Linear 3 2 4 R R R R 2 2 2 2 5 13 Tri Non 4 7 Linear 3 3 3 3R 6R 4R 7R 3 6 Work (w) Work done by the system = Negative Reversible Irreversible Heat given to system = Positive V2 Heat given by the system = Negative w rev = – ∫ Pext.dV wirr = –Pext (V2–V1) V1 Internal Energy (E & U) Sign Convention Every system having some quantity of matter is associated with a definite amount of energy called internal energy. W (+)ve q U = UKinetics + UPotential + UElectronic + Unuclear +........ system First Law of Thermodynamics W (–)ve q Law of conservation of energy DU = q + w Work done on system = Positive Enthalpy H = U + PV, DH = DU + (Dng) RT Process Expression for w Expression for q Work on PV-graph V2 V  w = –nRT ln q = nRT ln  2  V1  V1  Reversible isothermal P1 P  = –nRT ln q = nRT ln  1  P2  P2  q=0 w = nCV(T2–T1) Reversible adiabatic PVg = constant P V –PV process = 2 2 1 1 TVg–1 = constant γ –1 TP1–g/g = constant Statements of Second Law of Thermodynamics (i) No cyclic engine is possible which take heat from one single source and in a cycle completely convert it into work without producing any change in surroundings. 14 NEET (XI) Module-2 PW  Source Some Facts to be Remembered (a) Standard condition E w For gases/solid/liquid P = 1 bar Sink For ion/substance in solution Concentration = 1M (ii) In an irreversible process entropy of universe increases but it remains constant in a reversible process. (b) DGr = (DGf)product – (DGf)reactant DSsyt + DSsur = 0 for rev. process DHr = (DHf)product – (DHf)reactant DSr = (DSf)product – (DSf)reactant DSsyt + DSsur > 0 for irrev. process (All above equation will be derived in thermochemistry) DSsyt + DSsurr ≥ 0 (In general) Thermochemistry Calculation of Entropy Change for an Ideal Gas Bond Enthalpy General Expression Average amount of enthalpy required to dissociate one mole T2 V T P gaseous bond into separate gaseous atoms. DS = nCV ln + nR= ln 2 nCP ln 2 + nR ln 1 T1 V1 T1 P2 DrH = (Sum of bond enthalpy of gaseous reactant) – (Sum of bond Reversible & irreversible isothermal expansion or contraction enthalpy of gaseous product) V of an ideal gas DS = nR ln 2 Resonance Energy V1 ∆H °resonance = DfH° (experimental) - DfH° (calculated) Third Law of Thermodynamics = DCH° (calculated) - DCH° (experimental) “At absolute zero, the entropy of a perfectly crytalline substance is zero”. which means that at absolute zero every crystalline solid is Enthalpy of Neutralization (DHneut) in a state of perfect order and its entropy should be zero. (Always exothermic) Variation of DSr with Temperature & Pressure Change in enthalpy when one gram equivalent of an acid is T2 completely neutralized by one g-equivalent of a base in dilute (DSr)T – (DSr)T = (DCP)r ln 2 1 T1 solution. P1 (DSr)P – (DSr)P = DngR ln SA + SB → salt + water; DH°neut 2 1 P2 Similarly H+(aq) + OH–(aq) → H2O(l); DH = –13.7 kcal eq–1 = 57.3 kJ eq–1 (DHr)T – (DHr)T = (DCP)r (T2–T1) {Krichoff's equation} 2 1 In case of weak acid/ base or both |DHN° | < 13.7 kcal/eq–1 and (DUr)T – (DUr)T = (DCV)r (T2–T1) 2 1 the difference is enthalpy of ionisation of weak species except in Gibbs Free Energy (G) and Spontaneity case of HF when |DHN| > 13.7 kcal/eq–1 due to hydration of F–. A new thermodynamic state function G, the Gibbs free energy is defined as: NOTES: In a reaction if heat of reactant & products are given G = H – TS then, heat of that reaction can be measured as follows: At constant temperature and pressure (a) For heat of combustion & for bond enthalpy DG = DH – T DS If (DG)T,P < 0 Process is irreversible (spontaneous) DrH = Σ(DHC)reactant – Σ (DHC)product (DG)T,P = 0 Process is reversible (b) For heat of formation (DG)T,P > 0 Process is impossible (non spontaneous) DrH = Σ(DHf)product – Σ (DHf)reactant P W Thermodynamics 15