Single Sex School

Topics: Ethanol fuel, Energy development, Enthalpy Pages: 36 (1207 words) Published: March 14, 2013
TABLE OF CONTENTS

6.1
 
 The
 Nature
 of
 Energy
  6.2
 
 Enthalpy
 and
 Calorimetry
  6.3
 
 Hess’s
 Law
  6.4
 
 Standard
 Enthalpies
 of
 FormaCon
  6.5
 
 Present
 Sources
 of
 Energy
  6.6
 
 
 New
 Energy
 Sources
 

30

STANDARD ENTHALPIES OF FORMATION

Cgraphite(s)
 
 Cdiamond(s)

ΔH
 for
 this
 process
 cannot
 be
 obtained
 
 
 
 by
 direct
 measurement
 in
 a
 calorimeter
  but
 can
 be
 calculated
 from
 heats
 of
 combusCon.
 

CH4(g)
 +
 2O2(g)
 
 CO2(g)
 +
 2H2O(l)
ΔH°
 for
 this
 process
 can
 be
 calculated
 
  from
 the
 standard
 enthalpy
 of
 formaCon
 (ΔHf°).
 

In
 Appendix
 4
 

31

STANDARD ENTHALPIES OF FORMATION

The
 standard
 enthalpy
 of
 forma1on
 of
 a
 compound
 is
 
 
 
 the
 change
 in
 enthalpy
 that
 accompanies
 the
 formaCon
 of
 
 
 
 one
 mole
 of
 a
 compound
 from
 its
 elements
 
 
 
 with
 all
 substances
 in
 their
 standard
 states.
 
1/2N2(g)
 +
 O2(g)
 
 NO2(g)
 
 
 ΔHf°
 =
 34
 kJ/mol
 
 ΔHf°
 =
 -­‐239
 kJ/mol

C(s)
 +
 2H2(g)
 +
 1/2O2(g)
 
 CH3OH(l)

In
 Appendix
 4
 

32

STANDARD ENTHALPIES OF FORMATION
Conven1onal
 Defini1ons
 of
 Standard
 States
 
  For
 a
 Compound,
    The
 standard
 state
 of
 a
 gaseous
 substance
 is
 a
 pressure
 of
 exactly
 1
 atm.
    For
 a
 pure
 substance
 in
 a
 condensed
 state
 (liquid
 or
 solid),
 the
 standard
 state
 is
 the
 pure
  liquid
 or
 solid.
    For
 a
 substance
 present
 in
 a
 solu>on,
 the
 standard
 state
 is
 a
 concentra>on
 of
 exactly
 1
 M.
 
  For
 an
 Element,
    The
 standard
 state
 of
 an
 element
 is
 the
 form
 in
 which
 the
 element
 exists
 under
 condi>ons
  of
 1
 atm
 and
 25°C.
 
 
 
 The
 standard
 state
 of
 oxygen
 is
 O2(g)
 at
 a
 pressure
 of
 1
 atm
 
 
 The
 standard
 state
 for
 sodium
 is
 Na(s)
 
 
 The
 standard
 state
 for
 mercury
 is
 Hg(l)
  C(s)
 +
 2H2(g)
 
 CH4(g)
 

1/2N2(g)
 +
 O2(g)
 
 NO2(g)
 
 
  H2(g)
 +
 1/2O2(g)
 
 H2O(l)
  C(s)
 +
 2H2(g)
 +
 1/2O2(g)
 
 CH3OH(l)

33

STANDARD ENTHALPIES OF FORMATION
Examples
 of
 standard
 enthalpies
 of
 formaCon
  standard
  state
 

1/2N2(g)
 +
 O2(g)
 
 NO2(g)
  ( (

 
 
 )
 +
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