ENG_sgwhk04 - The statement of the first law of...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
1 The statement of the first law of thermodynamics Δ U = Q + W (closed system or d U = δ Q + δ W (closed system δ Q and δ W are process quantities tiny quantities, they could not be differentiated W 0 The work done by surroundings to the system (System gains energy in work form) W 0 The work done by system to its surrounding System loses energy in work form) Q 0 The system absorbs heat from its surroundings (System gains energy in form of heat) Q 0 The system releases heat to its surroundings (System loses energy in form of heat)
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Understanding the thermodynamic energy at a microscopic point of view U The energy inside the system T+V of all particles in the system T+V inside particles The internal energy is a state function and extensive quantity. For a process from A to B Δ U = U ( B ) -U ( A ) U Internal energy ( 内能) or Thermodynamic energy ( 热力学能 )
Background image of page 2
3 Enthalpy: Any uniform single phase system at equilibrium, the state function U + pV is defined as enthalpy of the system, and is denoted H 1 Enthalpy is an extensive property 2 Enthalpy is one of properties of a system at equilibrium. It is independent of process, and its change equals Q p only for a closed system undergoing an isobaric process. Δ H = H 2 -H 1 = U 2 +pV 2 - U 1 +pV 1 = Q p def HU p V +
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 1 All heat absorbed by a system in a isobaric process without other work is used to increase the enthalpy; 2 The absolute value of enthalpy can not be determined since the internal energy is unknown; 3 In all processes the enthalpy has defined value, but does not equal to Q p ; 4 H differs from U for that it can be changed in an isolated system H 2 , O 2 H 2 O Δ H=U 2 -U 1 +p 2 V-p 1 V = V ( p 2 - p 1 )<0 Important points:
Background image of page 4
5 For any object (or system) the heat capacity is the heat absorbed when the temperature of the object has risen an unit degree. It is the thermodynamic response function . 2.4 Heat capacity ( 热容 ) The definition dT Q T T Q T C T T δ δ lim ) ( 0 0 = = Average C from T to T 0 unit J.K -1 -4 th lecture-
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
6 Molar heat capacity T Q n T C d 1 def ) ( m δ unit: J.K -1 .mol -1 Isochoric molar heat capacity ( 等容摩尔热容 ) V V V V T U n T Q n n T C T C = = 1 d δ 1 ) ( def ) ( m , Fixed composition no chemical reaction no phase change closed system isochoric process W ′= 0 Definition δ Q = d U - δ W
Background image of page 6
7 Isobaric molar heat capacity( 等压摩尔热容 ) p p p p T H n T Q n n T C T C = = 1 d δ 1 ) ( def ) ( m , Fixed composition no chemical reaction no phase change closed system isobaric process W ′= 0 δ Q p = d H Definition
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
8 1 C is not a state function of system and depends on process 2 C V,m ( T,V ), C p,m ( T,P ) are intensive properties of system, and relating to T p V Important points
Background image of page 8
9 The above equations are valid for calculation of Δ U Δ H in pure change of temperature of gas under conditions of constant-volume and
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 42

ENG_sgwhk04 - The statement of the first law of...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online