厦门大学：《物理化学 Physical Chemistry》课程电子教案（PPT教学课件，英文版）chapter02 The First Law of Thermodynamics

Physical chemistr Physical Chemistry Cheng Xuan February 2004, Spring Semester

1 Physical Chemistry Cheng Xuan February 2004, Spring Semester Physical Chemistry

Physical Chemistry Summary Ideal gases/Perfect gases Key Notes e Gases: a fluid which has no intrinsic shape and which e expands indefinitely to fill any container in which it is held The ideal gas equations: the relations among the amount of gas substance, temperature, pressure and volume PV=nRT PYm=RT Vm: molar gas volume

3 Key Notes Ideal Gases/Perfect Gases Physical Chemistry Summary Gases: a fluid which has no intrinsic shape, and which expands indefinitely to fill any container in which it is held. The ideal gas equations: the relations among the amount of gas substance, temperature, pressure and volume. PV = nRT PVm = RT Vm: molar gas volume

Physical Chemistry Summary Ideal gases/Perfect gases Key Notes e Partial pressure: the pressure exerted by each component In a gaseous mixture P=nrt/v n. mole irp total x;: mole fraction e Dalton's law: the total pressure exerted by a mixture of ideal gases in a volume is equal to the arithmetric sum of the partial pressures total niota rT/y

4 Key Notes Ideal Gases/Perfect Gases Physical Chemistry Summary Dalton’s law: the total pressure exerted by a mixture of ideal gases in a volume is equal to the arithmetric sum of the partial pressures. Ptotal = ntotalRT/V Partial pressure: the pressure exerted by each component in a gaseous mixture. Px = nxRT/V Pi = xiPtotal nx : mole xi : mole fraction

Physical Chemistry Chapter 2 CHAPTER 2 -. The First Law of Thermodynamics Basic Concepts Isothermal A system which is held at constant temperature Adiabatic: A system in which energy may be transferred as work but not as heat Diathermic: a system which allows energy to escape as heat through its boundary if there is a difference in temperature between the system and its surroundings

5 Isothermal: A system which is held at constant temperature Adiabatic: A system in which energy may be transferred as work, but not as heat. CHAPTER 2 The First Law of Thermodynamics Basic Concepts Diathermic: A system which allows energy to escape as heat through its boundary if there is a difference in temperature between the system and its surroundings. Physical Chemistry Chapter 2

Physical Chemistry Chapter 2 Interna l Energy Internal energy: Total amount of energy in a system. The sum total of all kinetic and potential energy within the system Internal energy changes: The sign of AU Negative values: a system loses energy to the surroundings Positive values: a system gains energy from the surroundings

6 Internal energy: Total amount of energy in a system. The sum total of all kinetic and potential energy within the system. Internal energy changes: The sign of U Negative values: a system loses energy to the surroundings Positive values: a system gains energy from the surroundings Physical Chemistry Chapter 2 Internal Energy

Physical Chemistry Chapter 2 Thermodynamic Properties of system Extensive property: The value of the property changes according to the amount of material which is l present( e. g, mass, volume, internal energy) e Intensive property: independent of the amount of material which is present(e.g temperature, density) State functions: the value of a particular property for a system depends solely on the state of the system at time(e.g, pressure, volume, internal energy, entropy Path functions: A property depends upon the path by e which a system in one state is changed into another state(e.g, work, heat

7 Extensive property ： The value of the property changes according to the amount of material which is present (e.g., mass, volume, internal energy) Intensive property：independent of the amount of material which is present (e.g., temperature, density) Thermodynamic Properties of system State functions: the value of a particular property for a system depends solely on the state of the system at time (e.g., pressure, volume, internal energy, entropy) Path functions: A property depends upon the path by which a system in one state is changed into another state (e.g., work, heat) Physical Chemistry Chapter 2

Physical Chemistry Chapter 2 Work Work: the transfer of energy as orderly motion due to energy being expanded against an opposing force(in mechanical terms) dw= F dx (210)* Reversible p-v work dwrey =-Pdv closed system, reversible process (2.30)* rey Pdv closed system, reversible process(2.31)

8 Work: the transfer of energy as orderly motion due to energy being expanded against an opposing force (in mechanical terms) Physical Chemistry Chapter 2 Work dw  Fx dx (2.10)* Reversible P-V Work wrev PdV 2 1 = − closed system, reversible process (2.31) dw (2.30)* rev = -PdV closed system, reversible process

Physical Chemistry Chapter 2 Reversible p-v work dx -F=F=PA Piston moving- (a) Expansion(dv>0) F、=F=PA Piston moⅴing g (b) Compression(dv <0

9 Reversible P-V Work (a) Expansion (dV > 0) (b) Compression (dV < 0) V dx Piston moving Fx=F=PA V dx Piston moving Fx=F=PA Physical Chemistry Chapter 2

Physical Chemistry Chapter 2 Heat: the transfer of energy as disorderly motion as e the result of a temperature difference between the system and its surroundings exothermic: a process that releases energy as heat (all combustion reactions endothermic: processes that adsorb energy as heat (the vaporization of water an adiabatic system a)an an endothermic exothermic process process 10

10 exothermic: a process that releases energy as heat (all combustion reactions) endothermic: processes that adsorb energy as heat (the vaporization of water) Heat: the transfer of energy as disorderly motion as the result of a temperature difference between the system and its surroundings. (a) (b) Physical Chemistry Chapter 2 an adiabatic system (a) an endothermic process (b) an exothermic process

Physical Chemistry Chapter 2 Heat: the transfer of energy as disorderly motion as the result of a temperature difference between the system and its surroundings endothermic: energy enters as heat from the surroundings, the system remains at the same T(c) exothermic: energy leaves as heat from the system, the system remains at the same T(d) a diathermic container Heat An Heat ISothermal ocess (d)

11 Heat: the transfer of energy as disorderly motion as the result of a temperature difference between the system and its surroundings. Heat (c) Heat (d) a diathermic container Physical Chemistry Chapter 2 endothermic: energy enters as heat from the surroundings, the system remains at the same T (c) exothermic: energy leaves as heat from the system, the system remains at the same T (d) An isothermal process