PART- Chemical Thermodynamics and Thermochemistry Reference: Chapter 6 in textbook
1 PART 9 – Chemical Thermodynamics and Thermochemistry Reference: Chapter 6 in textbook
Basic Concepts System, Surroundings and Universe System Surrounding Universe Open System Both mass and energy exchange exist between the System and the Surroundings Close System Only energy(not mass)exchange exists between the System and the Surroundings Isolated System Neither energy nor mass exchange exists between the System and the Surroundings
Basic Concepts System, Surroundings and Universe System + Surrounding = Universe Open System Both mass and energy exchange exist between the System and the Surroundings. Close System Only energy (not mass) exchange exists between the System and the Surroundings. Isolated System Neither energy nor mass exchange exists between the System and the Surroundings. 2
State and state Function o State State: ensemble of all physical and chemical properties of a system ■ Example I mol H2 1 mol H 0°C.1atm 00C.0.5atm 22.4dm3 44.8dm State 1 State 2 3
State and State Function State State: ensemble of all physical and chemical properties of a system Example: 3 1 mol H2 1 mol H2 0 ºC , 1 atm 0 ºC , 0.5 atm 22.4 dm3 44.8 dm3 State 1 State 2
State and state Function State Function (State Quantity, State Variable) A property of a system that depends only on the current state of the system, not on the way how the system acquired that state, (i.e. independent of path) Only depends on the initial state and the final state H2O(s,25°C,1atm) H2O(g,25°C,1atm) H2O(,25°C,1atm)
State and State Function State Function (State Quantity, State Variable) A property of a system that depends only on the current state of the system, not on the way how the system acquired that state, (i.e. independent of path). Only depends on the initial state and the final state. 4 H2O (s, 25 ºC, 1atm ) H2O (g, 25 ºC, 1atm ) H2O (l, 25 ºC, 1atm )
Energy Internal Energy(U) The sum of all types of energy of a system: e.g Chemical bond, van der Waals interaction Movement of molecules molecular vibration We cannot know the absolute value of u but we can measure the change of U, (i.e. AU) Q: If the system takes two different paths to change from State 1 to State 2, which path has larger AU?
Energy Internal Energy (U) The sum of all types of energy of a system: e.g. Chemical bond, van der Waal’s interaction, Movement of molecules, Molecular vibration, … We cannot know the absolute value of U, but we can measure the change of U, (i.e. ΔU). Q: If the system takes two different paths to change from State 1 to State 2, which path has larger ΔU? 5
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 )
