5.111 Lecture Summary #15 Friday, October 10, 2014
Readings for today: Sections 7.13, 7.15, 7.16, 7.17, 7.18, and 7.20 (Sections 6.13, 6.15,
6.16, 6.17, 6.18, and 6.20 in 4th ed) – The Enthalpy of Chemical Change.
Read for Lecture #16: Section 8.1 (Section 7.1 in 4th ed) – Spontaneous Change, Sections
8.2 and 8.8 (Sections 7.2 and 7.8 in 4th ed) - Entropy, Sections 8.12, 8.13, 8.15 (Sections
7.12, 7.13, 7.15 in 4th ed) – Free Energy.
Announcements: Extra problems for exam 2 will be posted today.
Topics: Introduction to Thermodynamics
A. Bond energy/ bond enthalpy (∆HB)
B. Enthalpies of reaction (∆Hr)
C. Methods to calculate ∆Hr
INTRODUCTION TO THERMODYNAMICS
In the study of a given reaction, thermodynamics deals with the
associated with the reaction, while kinetics deals with the
of the reaction (lecture 30).
For example the conversion of diamonds to graphite is thermodynamically favorable.
“Diamonds are forever" is therefore a statement.
A. BOND ENERGY/ BOND ENTHALPY
Bond (dissociation) energy, ΔEd, is the energy required to break a bond.
CH4 → CH3 + H
Energy
CH3 + H
ΔEd
CH4
r⇒
∆HB , bond , is the change in heat accom panying the dissociation of a
bond (measured at constant pressure P).
∆H = ∆E + ∆(PV)
For gases, ∆H & ∆ E differ by %. For liquids and solids, negligible difference.
∆HB (bond enthalpies) are always positive– it always takes energy (heat) to break a
bond. Bond breaking is always endothermic (heat must be added), whereas bond
form ation is always (heat released).
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Readings for today: Sections 7.13, 7.15, 7.16, 7.17, 7.18, and 7.20 (Sections 6.13, 6.15,
6.16, 6.17, 6.18, and 6.20 in 4th ed) – The Enthalpy of Chemical Change.
Read for Lecture #16: Section 8.1 (Section 7.1 in 4th ed) – Spontaneous Change, Sections
8.2 and 8.8 (Sections 7.2 and 7.8 in 4th ed) - Entropy, Sections 8.12, 8.13, 8.15 (Sections
7.12, 7.13, 7.15 in 4th ed) – Free Energy.
Announcements: Extra problems for exam 2 will be posted today.
Topics: Introduction to Thermodynamics
A. Bond energy/ bond enthalpy (∆HB)
B. Enthalpies of reaction (∆Hr)
C. Methods to calculate ∆Hr
INTRODUCTION TO THERMODYNAMICS
In the study of a given reaction, thermodynamics deals with the
associated with the reaction, while kinetics deals with the
of the reaction (lecture 30).
For example the conversion of diamonds to graphite is thermodynamically favorable.
“Diamonds are forever" is therefore a statement.
A. BOND ENERGY/ BOND ENTHALPY
Bond (dissociation) energy, ΔEd, is the energy required to break a bond.
CH4 → CH3 + H
Energy
CH3 + H
ΔEd
CH4
r⇒
∆HB , bond , is the change in heat accom panying the dissociation of a
bond (measured at constant pressure P).
∆H = ∆E + ∆(PV)
For gases, ∆H & ∆ E differ by %. For liquids and solids, negligible difference.
∆HB (bond enthalpies) are always positive– it always takes energy (heat) to break a
bond. Bond breaking is always endothermic (heat must be added), whereas bond
form ation is always (heat released).
1
