CHAPTER 7: Chemical
Thermodynamics I: Heat,
Work, and Energy

Thermodynamics-the study of
heat or energy flow (3 LAWS)

Contrast open, isolated, and
closed systems:  open- matter and energy 
closed -energy
isolated- neither

First Law- the total energy (E)
of the universe is constant
(Law of conservation of
energy)

                                    E= q + w
 E = Ef - Ei

Sign conventions:

q and w are positive if flow is
into system

negative if it is reversed


Exothermic - a process in
which heat flows out of the
system.  H<0 (negative)

Endothermic- a process in
which heat flows into the
system.  H>0 (positive)


Energy- the capacity to do
work (w) and transfer heat (q).

w = -Pex(Vf -Vi)

Kinetic and Potential

The SI unit of Energy is the
Joule(J, kgm2/s2)


ENTHALPY ( H ) Heat energy
transferred at constant
pressure.

 H=Hfinal-Hinitial=qp= E +P V


State Function-a function
whose value is independent of
path  (is determined only by
the initial and final points). H
and  E are  state
functions

Properties of  H 
-reverse sign on rev. Rx
-proport to amount (extensive
-depends on physical state 
-additive


Calculate the amount of heat
given off in the combustion of
100. g of CH4 if  H= -890. kJ

CH4(g)+2O2(g) CO2(g)+2H2O(
l

Measurement of  H
-Hess's Law
-Heat of formation,  Hf
-calorimetry

Hess's Law- the enthalpy
change for an overall reaction
is the sum of the enthalpy
changes for reactions that sum
to the overall Rx.
 1) A   B   H1
 2) B    C   H2
 3) A   C   H3=  H1 +  H2


Calculate the  HRx for:
                            C(diamond)  C(graphite)
from the following information
                                             
                                     H(kJ)
C(diam)+O2(g)  CO2(g) -395.4
CO2  C(graph)+O2(g)(g) 393.5
C(diam)  C(graph) -1.9

Calculate  H for the reaction of
lead and oxygen to give PbO
from the following information.
(Hess's Law)
Pb(s)+CO(g)   PbO(s)+C(s)
2C(s) + O2(g)   2CO(g)

if the individual  H's are 
-106.8kJ and -221.0kJ


Calculate  H for the following,
2S(s)+2OF2(g) SO2(g)+SF4(g)
from:
OF2(g)+H2O(l) O2(g)+2HF(g)
SF4(g)+2H2O(l) SO2(g)+4HF(g
S(s)+O2(g) SO2(g)
if the individual  H's are 
-276.6, -827.5, and -296.9 kJ.


Measurement of  H
-Hess's Law
-Heat of formation,  Hf
-calorimetry


The standard molar enthalpy of
formation ( Hfo) is the enthalpy
change for the formation of
one mole of a substance from
its elements all in their
standard states (298K, 1
ATM). (Given in Table 7.4)
the  Hfo for an element (in its
standard state) is ZERO.



Calculat. of  HoRx from  Hof
 HoRx=  Hof products-  Hof reactants

Calculate  HRx for the following:
Table 7.4

CH4(g)+2O2(g) CO2(g)+2H2O(
l) 

Calculate the heat of formation
of napthalene from its heat of
combustion data (Table 7.5)
and Table 7.4

Measurement of  H
-Hess's Law
-Heat of formation,  Hfo
-calorimetry

Calorimeter-a device for
measuring heat changes.
cup-constant pressure
bomb-constant volume

q= -C T

 T= TFinal - Tinitial

C is the heat capacity of the
calorimeter and is determined
by calibration with a compound
of known heat of combustion
as illustrated in the next
example


        Exercise 7-6

Calculate the calorimeter
constant if combustion of a
2.000 g sample of napthalene
(-5153.9 kJ/mol)  in a
calorimeter caused the
temperature to increase from
26.50 to 27.68 0. 

Calculate  H  and  E if
combustion of 3.210 g of
pentane in the same device
caused the temp to increase
from 25.50 to 26.69o.

Consider 7.21