View
224
Download
0
Category
Preview:
Citation preview
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 1/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
1
Energy
The capacity to do work
or to produce heat.
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 2/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
2
Law of Conservation
of Energy
Energy can be converted from one form to
another but can neither be created nor
destroyed.
( E universe is constant)
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 3/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
3
The Two Types of Energy
Potential: due to position or composition -
can be converted to work
Kinetic: due to motion of the object
KE = 1 / 2mv2
(m = mass, v = velocity)
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 4/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
4
Temperature v. Heat
Temperature reflects random motions of
particles, therefore related to kinetic energy
of the system.
Heat involves a transfer of energy between
2 objects due to a temperature difference
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 5/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
5
State Function
Depends only on the present state of the
system - not how it arrived there.
It is independent of pathway.
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 6/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
6
System and Surroundings
System: That on which we focus attention
Surroundings: Everything else in the universe
Universe = System + Surroundings
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 7/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
7
Exo and Endothermic
Heat exchange accompanies chemicalreactions.
Exothermic: Heat flows out of the system(to the surroundings).
Endothermic: Heat flows into the system
(from the surroundings).
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 8/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
8
First Law
First Law of Thermodynamics:
The energy of the universe is
constant.
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 9/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
9
Figure 6.2
The Combustion of Methane
Fi 6 3
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 10/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
10
Figure 6.3
The Energy Diagram for the Reaction of Nitrogen and Oxygen to
Form Nitric Oxide
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 11/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
11
First Law
E = q + w
E = change in system’s internal energy
q = heat
w = work
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 12/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
12
Work
work = force distance
since pressure = force / area,
work = pressure volume
wsystem = PV
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 13/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
13
Figure 6.4
The Volume of a
Cylinder
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 14/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
14
Enthalpy
Enthalpy = H = E + PV E = H PV
H = E + PV
At constant pressure,
qP = E + PV ,
where qP = H at constant pressure
H = energy flow as heat (at constant pressure)
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 15/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
15
Figure 6.5
A Coffee-Cup Calorimeter Made of
Two Styrofoam Cups
Fi 6 6
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 16/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
16
Figure 6.6
A Bomb Calorimeter
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 17/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
17
Heat Capacity
C =heat absorbed
increase in temperature =J
C or J
K
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 18/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
18
Some Heat Exchange Terms
specific heat capacity
heat capacity per gram = J/°C g or J/K g
molar heat capacity
heat capacity per mole = J/°C mol or J/K mol
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 19/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
19
Hess’s Law
Reactants Products
The change in enthalpy is the same whether
the reaction takes place in one step or a
series of steps.
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 20/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
20
Figure 6.7
The Principle of Hess’s Law
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 21/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
21
Calculations via Hess’s Law
1. If a reaction is reversed, H is also reversed.N2(g) + O2(g) 2NO(g) H = 180 kJ
2NO(g) N2(g) + O2(g) H = 180 kJ
2. If the coefficients of a reaction are multiplied
by an integer, H is multiplied by that same
integer.6NO(g) 3N2(g) + 3O2(g) H = 540 kJ
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 22/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
22
Standard States
Compound
• For a gas, pressure is exactly 1 atmosphere.
• For a solution, concentration is exactly 1 molar.
• Pure substance (liquid or solid), it is the pure liquid or
solid.
Element
• The form [N2(g), K(s)] in which it exists at 1 atm and
25°C.
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 23/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
23
Standard Heat of Formation
H f
H of a reaction in which one mole of a product
is made from elements
)()(2
1)(
2
122
g NOgOg N
H f (NO) = H rxn
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 24/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
24
Change in Enthalpy
Can be calculated from enthalpies of
formation of reactants and products.
H rxn° = np H f (products) nr H f (reactants)
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 25/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
25
Figure 6.8
Pathway for the Combustion of Methane
Figure 6 9
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 26/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
26
Figure 6.9
A Schematic Diagram of the Energy Changes for the Reaction
CH4(g) + 2O2(g) CO2(g) + 2H2O(l)
7/29/2019 Chemistry Thermodynamics
http://slidepdf.com/reader/full/chemistry-thermodynamics 27/28
Copyright©2000 by HoughtonMifflin Company. All rights reserved.
27
Bond Energy
• Bond energy is the energy required to break
a bond.
• Breaking a bond is always endothermic.
• Bond formation is always exothermic.
• May use bond energies to approximate
H rxn
Recommended