Heat and work Two forms of energy exchange between the System and the Surroundings They are NOT State Functions!! Heat( Q Energy exchange due to the temperature difference between the System and the Surroundings Work(W) All other energy exchange forms(other than Heat between the System and the surroundings e.g. Mechanical work, Electric work, Interfacial work, Expansion work, Compression work,(Volume work).6
Heat and Work Two forms of energy exchange between the System and the Surroundings – They are NOT State Functions!!! Heat (Q) Energy exchange due to the temperature difference between the System and the Surroundings Work (W) All other energy exchange forms (other than Heat) between the System and the Surroundings e.g. Mechanical work, Electric work, Interfacial work, Expansion work, Compression work, (Volume work)… 6
Molar Heat Capacity Molar Heat Capacity(C, unit: energy/mol) Heat needed to increase 1 mol of substance for 1 oC Total heat needed: Q=n(mo)*C*(T -) Under the constant pressure condition>Cp Under the constant volume condition >Cy Molar heat capacity of ideal gases Monatomic molecular gas(e.g. He, Ne, Ar,...) Cy= 3/2R: CD=Cu +r=5 2R Diatomic molecular gas(e.g. H2, O2, HCl,.) CV=5/2R, Cp= Cv+R=7 R 7
Molar Heat Capacity Molar Heat Capacity (C, unit: energy/mol): Heat needed to increase 1 mol of substance for 1 oC. Total heat needed: Q = n (mol) * C * (Tfinal – Tinitial) Under the constant pressure condition CP Under the constant volume condition CV Molar heat capacity of ideal gases: Monatomic molecular gas (e.g. He, Ne, Ar, …): CV = 3/2 R; CP = CV + R = 5/2 R Diatomic molecular gas (e.g. H2 , O2 , HCl, …): CV = 5/2 R; CP = CV + R = 7/2 R 7
Extensive Property, Intensive Property EXtensive Property Properties that depend on the quantity of samples measured, and can be added up e.g. Mass(m), Volume(v), Heat capacity(Cp), Internal energy(U), Enthalpy(h), Entropy(s) Free energy(G) Intensive Property Properties that are independent on the quantity of samples measured, and cannot be added up e.g. Temperature(D), Density(d), Concentration(C)
Extensive Property, Intensive Property Extensive Property Properties that depend on the quantity of samples measured, and can be added up. e.g. Mass (m), Volume (V), Heat capacity (CP ), Internal energy (U), Enthalpy (H), Entropy (S)、Free energy (G) Intensive Property Properties that are independent on the quantity of samples measured, and cannot be added up. e.g. Temperature (T), Density (d), Concentration (C) 8
Thermodynamics 1st Law First Law-Energy Conservation (1)Energy cannot be created or destroyed. (2)Total energy of the universe is constant Math representation △U=Q-W AU:(+) means increase of the Systems energy (means decrease of the Systems energy Q: (+)means the System absorbs heat, i.e. endothermic (means the Systems gives of heat, i.e. exothermic W: (+) means the System does work to the Surroundings (means the Surroundings does work to the System 9
Thermodynamics 1st Law First Law – Energy Conservation (1) Energy cannot be created or destroyed. (2) Total energy of the universe is constant. Math representation: ΔU = Q – W ΔU: (+) means increase of the System’s energy; (-) means decrease of the System’s energy. Q: (+) means the System absorbs heat, i.e. endothermic; (-) means the Systems gives of heat, i.e. exothermic. W: (+) means the System does work to the Surroundings; (-) means the Surroundings does work to the System. 9
Practice Q1: If a system(below) follows Path 1 the white arrow) to change from the initial state to the final state the system absorbed 3000 J of heat, and the work done by the system to the surroundings was 2500 J (a How much the internal energy(U)was changed? (b) If the system follows Path 2( the yellow arrow )to change, how much the internal energy was changed? 「roar)≤o;a、r、;k01、T1 latm), U1 atm H2O(L,100°C,1atm)→)H2O(g,100C,1atm)
Practice Q1: If a system (below) follows Path 1 (the white arrow) to change from the initial state to the final state, the system absorbed 3000 J of heat, and the work done by the system to the surroundings was 2500 J. (a) How much the internal energy (U) was changed? (b) If the system follows Path 2 (the yellow arrow) to change, how much the internal energy was changed? 10 H2O ( l, 25 ºC, 1atm ), U1 H2O ( g, 25 ºC, 1atm ), U2 H2O ( l, 100 ºC , 1atm ) H2O ( g, 100 ºC, 1atm )