[国家级精品课程]物理化学双语课件2-1-chapter 2 Entropy-concept-Eng

The structure of a heat engine
Central South University
Characteristics of spontaneous process
The spontaneous process (自发过程）
are always accompanied by a dispersal of energy into a more disordered form.
Chapter 2 Entropy and
The Second Law of Thermodynamic
——2-1 Entropy
(acknowledge to reference of Peter Atkins`s Physical Chemistry ,7th )
Central South University
Formation of water - SPONTANEOUS! 2H2(g) + O2(g) Pt cat 2H2O(l) H = - 285.8 kJ.mol-1
However, the dissolution of ammonium
nitrate is also spontaneous, but it is also endothermic.
（熵的热力学定义）
For a measurable change between two states i and f this expression integrates to:
S
f
Qrev
T
f
i
S f Si
Qrev.
T
i
Central South University
Property of Entropy (熵的性质）
• Clausius inequality
Central South University
热力学第二定律 The Second Law of Thermodynamic
1. Spontaneous Process
Central South University
Characteristics of spontaneous process 自发过程的特点
Central South University
Characteristics of spontaneous process 自发过程的特点
But some things don't ： We can confine a gas to a smaller volume;
we can cool an object with a refrigerator, we
heat from a reservoir ( 热 源） and its
complete conversion into work （功）.
Central South University
热功转换效率
卡诺循环的效率
Central South University
卡诺循环
T1VB 1 T2VC 1
卡诺定理的意义：（1）解决了热机效率的极限值问题。
（2）引入不等号，原则上解决了化学反应的方向问题；
Entropy (熵）
1). The thermodynamic definition of entropy
（熵的热力学定义）
The thermodynamic definition of entropy is based on Keep Mind! Qrev Heat of reversible process dS T （可逆过程的热！）
NH4NO3(s) NH4+(aq) + NO3-(aq) H = +25.7 kJ.mol-1 So is: 2N2O5(s) 4NO2(g) + 2O2(g) H = +109.5 kJ.mol-1 a process does not have to be exothermic to be spontaneous.
Examples • Nails rusting outdoors
SPONTANEOUS PROCESS
• Ice melting at room temperature
• Expansion of gas into an evacuated space
• Formation of water from O2(g) and H2(g):
Why are some processes spontaneous and others not?
We know that temperature has an effect on the spontaneity of a process.
e.g. T>0oC ice melts spontaneous at this temp. H2O (s) H2O (l) T<0oC water freezes spontaneous at this temp. H2O (l) H2O (s)
Q3 Q1 Q2
First Law uses the internal energy to identify permissible changes.
（图片来自网站）
Central South University
Target:
Reaction direction limitation
Central South University
Central South University
Review: the First Law of Thermodynamic
△U = Q+ W
—the First Law of thermodynamics
only those change may occur for which the U of an isolated system remains constant.
Central South University
Exothermic processes tend to be spontaneous. Example
Rusting of nail - SPONTANEOUS! 4Fe(s) + 3O2(g) Fe2O3(s) H = - 822.2 kJ.mol-1
can force some reactions to go in reverse.
However, none of these processes happens
spontaneously（自发地）.
Central South University
SPONTANEOUS PROCESS

Transfer of Mass, creates fluid currents like in rivers or streams.
Configuration Chang
Central South University
Characteristics of spontaneous process 自发过程的特点
• spontaneous process are irreversible
• related to temperature and process heat
spontaneous process? The second law addresses these
Central South University
The Second Law of Thermodynamic
•Natural process
•2nd law of thermodynamics
• heat-temperature quotient and entropy
The units （单位）of entropy: J K -1. The units of Molar entropy: J K -1 mol –1 (the same as that of R)
Central South University
Entropy (熵）
1). The thermodynamic definition of entropy
2H2(g) + O2(g)
Pt cat 2H O(g) 2
Central South University
Review: the Second Law of Thermodynamic
热力学第二定律
Statements on the Second Law of Thermodynamic:
No process （ 过 程 ） is possible in which the sole result is the absorption of
Central South University
The dispersal of energy
The spontaneous changes are always accompanied by a dispersal of energy into a more disordered form.
Sketch for the distribution of energy
Some things happen naturally without any help：
(1) A gas expands to fill the available volume; (2) A hot body cools to the temperature of its surroundings ; (3) A chemical reaction runs in one direction rather than another.