Dr. L. Dawe
Chemistry 1050
Winter 2011
January 25 and 26, 2011 – Class 10 and 11 Overview
Chapter 7
•
Section 7.4 (Page 252 - 255): Work
–
Section 7.5 (Page 255 - 259): The First Law of Thermodynamics
•
–
Internal energy, state functions, path dependent functions
Section 7.6 (Page 259 - 265): Heats of Reaction: ΔU and ΔH
•
–
•
Pressure volume work and w = -Pext∆V
Constant pressure and constant volume reactions, enthalpy and
enthalpy and internal energy changes in chemical reactions. Heat as a
stoichiometric quantity in chemical reactions and phase changes.
Standard states and standard enthalpy changes and enthalpy diagrams.
Suggested end-of-chapter exercises: 47, 49, 51, 53, 55, 57, 65
Dr. L. Dawe
Chemistry 1050
Winter 2011
Work
When potassium chlorate decomposes it produces
oxygen gas. From the system’s point of view (which
is the convention), what is the sign of w?
1. Positive
2. Negative
3. Neutral; no
work done.
2 KClO3(s) 2KCl(s) + 3 O2(g)
Dr. L. Dawe
Chemistry 1050
Winter 2011
Work
When potassium chlorate decomposes it produces
oxygen gas. From the system’s point of view (which
is the convention), what is the sign of w?
1. Positive
2. Negative
3. Neutral; no
work done.
2 KClO3(s) 2KCl(s) + 3 O2(g)
Dr. L. Dawe
Chemistry 1050
Heats of Reaction: ∆U and ∆H
True or False: Boiling water evaporates to form snow.
Winter 2011
Dr. L. Dawe
Chemistry 1050
Heats of Reaction: ∆U and ∆H
True or False: Boiling water evaporates to form snow.
False: The process here is called solidification. It is exothermic.
Winter 2011
Dr. L. Dawe
Chemistry 1050
Winter 2011
Heats of Reaction: ∆U and ∆H
The figure below shows the heating curve for water. It traces the changes in
temperature as ice, initially at -20 oC, is gradually heated to produce liquid
water at +20 oC. Which of the following statements correctly describes what is
taking place at 0oC?
1.
Temperature remains constant,
therefore no heat is being added to
or removed from the system during
the melting of the ice.
2.
Although T is constant, heat is
added to convert H2O(s) to H2O(l)
3.
Although T is constant, heat is
removed to to convert H2O(s) to
H2O(l)
Dr. L. Dawe
Chemistry 1050
Winter 2011
Heats of Reaction: ∆U and ∆H
The figure below shows the heating curve for water. It traces the changes in
temperature as ice, initially at -20 oC, is gradually heated to produce liquid
water at +20 oC. Which of the following statements correctly describes what is
taking place at 0oC?
1.
Temperature remains constant,
therefore no heat is being added to
or removed from the system during
the melting of the ice.
2.
Although T is constant, heat is
added to convert H2O(s) to H2O(l)
3.
Although T is constant, heat is
removed to to convert H2O(s) to
H2O(l)
Dr. L. Dawe
Chemistry 1050
Winter 2011
Heats of Reaction: ∆U and ∆H
The figure below shows the cooling curve for water. It traces the changes
in temperature as water, initially at 20 oC, is gradually cooled to produce ice
at -20 oC. Which of the following statements correctly describes what is
taking place at 0oC?
1.
the temperature remains constant at 0 oC
and the process is exothermic.
2.
the temperature remains constant at 0 oC
and the process is endothermic.
3.
the temperature remains constant at 0 oC,
thus the process is neither endothermic
nor exothermic.
Dr. L. Dawe
Chemistry 1050
Winter 2011
Heats of Reaction: ∆U and ∆H
The figure below shows the cooling curve for water. It traces the changes
in temperature as water, initially at 20 oC, is gradually cooled to produce ice
at -20 oC. Which of the following statements correctly describes what is
taking place at 0oC?
1.
the temperature remains constant at 0 oC
and the process is exothermic.
2.
the temperature remains constant at 0 oC
and the process is endothermic.
3.
the temperature remains constant at 0 oC,
thus the process is neither endothermic
nor exothermic.
Dr. L. Dawe
Chemistry 1050
Winter 2011
Looking Ahead - January 27 and 31, 2011
Chapter 7
•
Section 7.7 (Page 266 - 268): Indirect Measurement of ΔH: Hess's
Law
–
•
Enthalpy change as an extensive property, sign change when process is
reversed, Hess's law of constant heat summation and enthalpy diagrams and
indirect determination of enthalpy changes
Section 7.8 (Page 268 - 275): Standard Enthalpies of Formation
–
Standard enthalpy of formation, standard states and the reference form of an
element and appropriate problems. Standard enthalpies of reaction from
standard enthalpies of formation (algebraic addition method and use of
equation 7.21). Standard enthalpy of formation of ions, H+(aq) as reference ion
and appropriate calculations involving Hess's law.
•
Section 7.9 (Page 275 - 280): Fuels as Sources of Energy
•
Suggested end-of-chapter exercises: 67, 69, 71, 73, 75, 79, 81, 93