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process①:W1≈0, process②:W2≈ - pVg = -nRT, △U2 = Q2 + W2= n△vapHm-nRT △H2 = Q2 = n△vapHm W3 = - p△V = - p(V1-V2) = nR(T2-T1) process③:△U3 = Q3 + W3, process④:△U4= △H4 = 0 △U = △U1 + △U2 + △U3 + △U4 △H = △H1 + △H2 + △H3 + △H4 irreversible phase transition §1-2.5 Application of the first law of thermodynamics (2) Chemical reaction 1-3 Thermochemistry 1-3 Thermochemistry Thermochemistry: a branch of thermodynamics, concentrating on the heat produced or required by chemical reactions. Process releasing heat-exothermic: ?rH 0 (isothermal and isobaric process) Process absorbing heat-endothermic: ?rH 0 (isothermal and isobaric process) As pex(i)=psys(i) - dpi, (Vi+1 -Vi) = dVi,n→∞ Wexp= -∑ pex(i) dVi = - ∑ pex(i) dVi + ∑ dpi dVi ≈ - ∑ pex(i) dVi = ∫ - pex dVi ∞ i =Ⅰ ∞ i =Ⅰ i =Ⅰ ∞ ∞ i =Ⅰ V2 V1 pex(Ⅰ) pex(n) V1 V2 Vi V If pex(i)=psys(i) + dpi,Wcontr.=∫ -psys. dVi= -Wexp. V2 V1 |Wcontr.| = | Wexp.| Reversible process with maximum work The internal energy, U : the total energy of a system is called its internal energy;it is the total kinetic and potential energy of the molecules composing the system. 2.2 Internal energy and the first law of thermodynamic 2.2.1 Definition of internal energy Positive and negative particles (ions) attract one another. Two atoms can bond As the particles attract they have a lower potential energy Kinetic energy — energy of motion. Potential Kinetic Energy NaCl — composed of Na+ and Cl- ions. 2.2.1 Definition of internal energy PE + KE = Internal energy (E or U) Int. E of a chemical system depends on number of particles type of particles temperature Potential Kinetic Energy 2.2.1 Definition of internal energy The internal energy is a state function. It is a extensive property. Internal energy, heat, and work are measured in the same units, the Joule (J). 2.2.1 Definition of internal energy 2.2.1 Definition of internal ene
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