第二章 热化学《化学原理》
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w = -P DV
(a) DV = 5.4 L – 1.6 L = 3.8 L P = 0 atm
W = -0 atm x 3.8 L = 0 L•atm = 0 joules
(b) DV = 5.4 L – 1.6 L = 3.8 L P = 3.7 atm
Attention:
E is a state function, but q and w are not a state function, since the latter two are only related to a process.
Exothermic process, gives off the heat to the surroundings.
No one knows how much the exact energy is!
The thermodynamics deals only with the energy changes that accompany chemical reactions.
System and Surroundings
System is the specific part of the universe that is of interest in the study.
Open system closed system Isolated system
mass & energy exchanged
only energy exchanged
Nothing exchanged
What we can measure is only the energy change!
(1) Heat is the energy transfer between a system and its surroundings that are at different temperatures.
Chapter 6 Thermochemistry
Energy change of chemical reaction.
WhatLeabharlann Baiduis the Energy?
It is the capacity to do work, and exists in a variety of the forms.
➢ Thermal energy the random motion. ➢ Chemical energy the bonds of substances ➢ Nuclear energy: neutrons and protons in the atom ➢ Electrical energy: the flow of electrons ➢ Potential energy: virtue of an object’s position
DEsystem + DEsurroundings = 0
The system energy change DE = Efinal - Einitial
DE = q + w
“+” gain by the system “–” lost by the system
q: the heat exchange with the surroundings. w: the work done on (or by) the system.
Temperature is a measure of the thermal energy. Temperature = Thermal Energy
900C greater thermal energy ?
400C
(2) Work, like heat, is the energy transfer between a system and its surroundings.
DE = Efinal - Einitial
Other changes:
DP = Pfinal - Pinitial DV = Vfinal - Vinitial DT = Tfinal - Tinitial
The potential energy of hiker 1 is the same as that of hiker 2.
Work (w) = Force (F) distance (h) = P A h = P DV Pressure-volume work
A
h
A
Thermodynamics
State functions determined only by the system state,
regardless of how it was achieved (i.e. history). Energy change:
2H2 (g) + O2 (g)
2H2O (l) + energy
H2O (g)
H2O (l) + energy
Endothermic process, gets the heat from the surroundings.
energy + 2HgO (s)
2Hg (l) + O2 (g)
A sample of nitrogen gas expands in volume from 1.6 L to 5.4 L at constant temperature. What is the work done in joules if the gas expands (a) against a vacuum and (b) against a constant pressure of 3.7 atm?
Significance it makes the reasoning and calculation simple.
The First Law of Thermodynamics:
The energy of the universe can be converted from one form to another, but it can not be created or destroyed.
(a) DV = 5.4 L – 1.6 L = 3.8 L P = 0 atm
W = -0 atm x 3.8 L = 0 L•atm = 0 joules
(b) DV = 5.4 L – 1.6 L = 3.8 L P = 3.7 atm
Attention:
E is a state function, but q and w are not a state function, since the latter two are only related to a process.
Exothermic process, gives off the heat to the surroundings.
No one knows how much the exact energy is!
The thermodynamics deals only with the energy changes that accompany chemical reactions.
System and Surroundings
System is the specific part of the universe that is of interest in the study.
Open system closed system Isolated system
mass & energy exchanged
only energy exchanged
Nothing exchanged
What we can measure is only the energy change!
(1) Heat is the energy transfer between a system and its surroundings that are at different temperatures.
Chapter 6 Thermochemistry
Energy change of chemical reaction.
WhatLeabharlann Baiduis the Energy?
It is the capacity to do work, and exists in a variety of the forms.
➢ Thermal energy the random motion. ➢ Chemical energy the bonds of substances ➢ Nuclear energy: neutrons and protons in the atom ➢ Electrical energy: the flow of electrons ➢ Potential energy: virtue of an object’s position
DEsystem + DEsurroundings = 0
The system energy change DE = Efinal - Einitial
DE = q + w
“+” gain by the system “–” lost by the system
q: the heat exchange with the surroundings. w: the work done on (or by) the system.
Temperature is a measure of the thermal energy. Temperature = Thermal Energy
900C greater thermal energy ?
400C
(2) Work, like heat, is the energy transfer between a system and its surroundings.
DE = Efinal - Einitial
Other changes:
DP = Pfinal - Pinitial DV = Vfinal - Vinitial DT = Tfinal - Tinitial
The potential energy of hiker 1 is the same as that of hiker 2.
Work (w) = Force (F) distance (h) = P A h = P DV Pressure-volume work
A
h
A
Thermodynamics
State functions determined only by the system state,
regardless of how it was achieved (i.e. history). Energy change:
2H2 (g) + O2 (g)
2H2O (l) + energy
H2O (g)
H2O (l) + energy
Endothermic process, gets the heat from the surroundings.
energy + 2HgO (s)
2Hg (l) + O2 (g)
A sample of nitrogen gas expands in volume from 1.6 L to 5.4 L at constant temperature. What is the work done in joules if the gas expands (a) against a vacuum and (b) against a constant pressure of 3.7 atm?
Significance it makes the reasoning and calculation simple.
The First Law of Thermodynamics:
The energy of the universe can be converted from one form to another, but it can not be created or destroyed.