Chapter 2 first law of TMD

38 751 1
Chapter 2   first law of TMD

Đang tải... (xem toàn văn)

Tài liệu hạn chế xem trước, để xem đầy đủ mời bạn chọn Tải xuống

Thông tin tài liệu

PHYSICAL CHEMISTRY Chapter – First law of thermodynamics Dr Ngo Thanh An Chapter – First law of thermodynamics Joule’s experiment As the weights fall, they give up potential energy and warm the water accordingly This was first demonstrated by James Joule, for whom the unit of energy is named Schematic diagram for Joule´s experiment Insulating walls to prevent heat transfer enclose water As the weights fall at constant speed, they turn a paddle wheel, which does work on water If friction in mechanism is negligible, the work done by the paddle wheel on the water equal the change of potential energy of the weights Chapter – First law of thermodynamics Internal energy Internal energy involves energy on the microscopic scale For thermochemistry  the internal energy is the sum of the kinetic energy of motion of the molecules, and the potential energy represented by the chemical bonds between the atoms and any other intermolecular forces that may be operative Chapter – First law of thermodynamics Statement of First law of thermodynamics ∆U = Q - A Chapter – First law of thermodynamics Statement of First law of thermodynamics U: state function ∆ U = Q1 – A1 = Q2 – A2 = Q3 – A3 For a infinitesimal process Where: “d” used for describing state function “δ” used for describing path function A1 Q1 Q2 A2 Q3 dU = δ Q − δ A A3 Chapter – First Law of Thermodynamics Statement of First law of thermodynamics Meaning of exact differential Chapter – First law of thermodynamics Heat vs Work Thermodynamic definition of work: It is a kind of interaction that would occur at the system boundaries It can be positive or negative Chapter – First law of thermodynamics Heat vs Work Chapter – First law of thermodynamics Heat vs Work Chapter – First law of thermodynamics Application of 1st law of TMD a Isochoric process (V = const or dV = 0) V2 dV = → Av = ∫V p.dV = ⇒ QV = ∆U Chapter – First law of thermodynamics Application of 1st law of TMD b Isobaric process (p = const or dp = 0) ⇒ Ap = ∫V p.dV = p ( V2 − V1 ) = p.∆V V2 ⇒ Q p = ∆U + A p = ∆U + p ∆V = ∆U + ∆(pV) = ∆(U + pV) = ∆H ⇒ QP = ∆H Enthalpy is the sum of internal energy and the product of pV Chapter – First law of thermodynamics Application of 1st law of TMD c Isobaric process for ideal gas Ideal gas equation pV = nRT : Ap = p ∆V = ∆(pV) = ∆(nRT) = nR∆T ⇒∆ Up = Qp – nR ∆ T or ∆ Up = ∆ H – nR ∆ T R: ideal gas constant, R = 1,987 cal/mol.K = 8,314 J/mol.K = 0,082 l.atm/mol.K Chapter – First law of thermodynamics Application of 1st law of TMD d Isothermal process for ideal gas Joule’s law: (for ideal gas) Internal energy of ideal gas just depends on temperature: U = f(T) ⇒ ∆U T = V2 V2 1 QT = AT = ∫V p.dV = ∫V nRT V2 p1 dV = nRT ln = nRT ln V V1 p2 Chapter – First law of thermodynamics Application of 1st law of TMD e Polytropic process Áp dụngnguyênlý 1: (1) Đặttỷlệtruyềnnănglượng: (2) Với (3) Ta sẽcó: (4) Biếtrằngphươngtrìnhkhíthực: (5) Ta có: (6) Ta cũngcó: (7) Thếphươngtrình (7) vàovếphảicủaphươngtrình (6), sẽcó: (8) Đặthệsố Đâychínhlàhệsốđoạnnhiệt Chia phươngtrình (8) chophươngtrình (4), sẽcó: (9) Nếuđặtgiátrị (10) Ta sẽcó: (11) Hay là: (12) Chapter – First law of thermodynamics Application of 1st law of TMD e Polytropic process Chapter – First law of thermodynamics Application of 1st law of TMD e Polytropic process Chapter – First law of thermodynamics Example A biatomic ideal gas undergoes a cycle starting at point A (2 atm, 1L) Process from A to B is an expansion at constant pressure until the volume is 2.5 L, after which is cooled at constant volume until its pressure is atm It is then compressed at constant pressure until the volume is again 1L, after which it is heated at constant volume until it is back in its original state Find (a) the work, heat and change of internal energy in each process (b) the total work done on the gas and the total heat added to it during the cycle A system consisting of 0.32 mol of a monoatomic ideal gas occupies a volume of 2.2 L, at a pressure of 2.4 atm The system is carried through a cycle consisting: The gas is heated at constant pressure until its volume is 4.4L The gas is cooled at constant volume until the pressure decreased to 1.2 atm The gas undergoes an isothermal compression back to initial point (a) What is the temperature at points A, B and C (b) Find W, Q and ΔU for each process and for the entire cycle Chapter – First law of thermodynamics Example Chapter – First law of thermodynamics Example Chapter – First law of thermodynamics Chapter – First law of thermodynamics Example Chapter – First law of thermodynamics Example Chapter – First law of thermodynamics Example [...]... 0, 1, 2, 2) 1 Chapter 2 – First law of thermodynamics 5 Specific heat capacity • For ideal gas: Cp = Cv + R Chapter 2 – First law of thermodynamics 5 Specific heat capacity Chapter 2 – First law of thermodynamics 5 Specific heat capacity • Constantpressure specific • heats for some gases Chapter 2 – First law of thermodynamics 6 Application of 1st law of TMD δ A = p.dV ⇒ ⇒ dU = δ Q − p.dV V2 ∆U =... Hay là: ( 12) Chapter 2 – First law of thermodynamics 6 Application of 1st law of TMD e Polytropic process Chapter 2 – First law of thermodynamics 6 Application of 1st law of TMD e Polytropic process Chapter 2 – First law of thermodynamics 7 Example A biatomic ideal gas undergoes a cycle starting at point A (2 atm, 1L) Process from A to B is an expansion at constant pressure until the volume is 2. 5 L,.. .Chapter 2 – First law of thermodynamics Heat vs Work Endothermic Chapter 2 – exothermic First law of thermodynamics Adiabatic system Work (A) Heat (Q) release >0

Ngày đăng: 25/09/2016, 17:47

Từ khóa liên quan

Mục lục

  • Slide 1

  • Slide 2

  • Slide 3

  • Slide 4

  • U: state function

  • Slide 6

  • Slide 7

  • Slide 8

  • Slide 9

  • Slide 10

  • Slide 11

  • Slide 12

  • Slide 13

  • Slide 14

  • Slide 15

  • Distinguish between heat, temperature, and thermal energy

  • Slide 17

  • Slide 18

  • Specific average heat capacity:

  • Slide 20

Tài liệu cùng người dùng

  • Đang cập nhật ...

Tài liệu liên quan