Download + I 2 (g,p )

Thermochemistry
Q p  H ( product）- H (reacant）  r H
 r H m   B H m ( B)
B




H
△rHm (298.15K)  B f m ( B)

(298.15K)
B
 r H m (298.15K)   B c H m (B, 298.15K)
B



H2(g,p ) + I2(g,p )=2HI(g,p )
△rHm(298.15K) = -51.8kJ·mol
Dependence of standard molar enthalpy of
Kirchhoff equation
reaction on temperature
 r H m (T1 )
+ bB
aA
 H1
H 2
+ bB
aA
 r H m (T2 )
yY
+ zZ
 H 4
H 3
yY
+ zZ
r H m T1   H1  H 2  r H m T2   H3  H 4
since
T2
 H  a  C p,m (A)d T,  H  b  C p,m (B)d T,

1
T1
H y

3
then
T2
T1

2
T2
T1
C p,m (Y)d T,  H   z 

4
T2
T2
T1
C p,m (Z)d T,
 r H m (T2 )   r H m (T1 )    BC p ,m ( B)dT
T
1
Heat of phase change
Q p  H
 H  H (  )  H ( )


From a liquid to a gas (vaporization)
From a solid to a liquid (fusion)
From a solid to a gas (sublimation)
Crystal form transition
W, Q, ΔU,ΔH of phase transformation
ΔH = ΔU + Δ(PV)=Q+W+△(PV)
For melting and crystal transition process at constant
pressure and constant temperature
Qp  H W   pV  0　U  H

For vaporization and sublimation processes
Qp  H
W   pV   pV ( g )  nRT
U  H  ( pV )  H  pV ( g )  H  nRT
Temperature dependence of enthalpy of phase
change
 H (T2 )  H m ( )   H (T1 )  H m (  )
T1
H m ( )   C p ,m ( )dT
T2
T2
H m (  )   C p ,m (  )dT
T1
Cp,m =C p ,m (  )-C p ,m ( )
T2
H m ( )+H m (  )   C p ,m dT
T1
T2
 H m (T2 )   H m (T1 )+  C p ,m dT
T1

1
373
K
,
P
, r H m
θ
θ   
 H2O(g, Pθ)
H2(g, P ) + O2(g, P )
2
ΔH4
H2O(l, Pθ,373K)
ΔH3
ΔH2

1
298
K
,
P
,  H m ,1
θ
θ   r 
 H2O(l, Pθ,298K)
H2(g, P ) + O2(g, P )
2
θ
Δ rH
θ
m(373K)
= Δ rH
=ΔrHθm(298K) +

373
298
m1
+ΔH2 +ΔH3 +ΔH4
ΔCPdT +ΔH4
Practice:
How high could the temperature get if
methane (CH4, g) deflagrate in air at 25℃
(CH4:O2=1:4molar ratio)，p≈100kPa?
T0=298.15K
CH4(g)1mol,O2 (g) 4mol
N2 (g) 15.05mol
Qp=H=0
T
CO2(g)1mol, H2O (g) 2mol
O2 (g) 2mol,N2 (g) 15.05mol
( )p,
adiabatic
rHm
H2
T0=298.15K
CO2(g)1mol, H2O (g) 2mol
O2 (g) 2mol,N2 (g) 15.05mol
Qp= H = rHm + H2 =0
H 2   C p ,m CO2 , g   2C p ,m H 2 O, g   2C p ,m O 2 , g   15.05C p ,m N 2 , g dT
T
T0
T =1477K
Home work





A: P89: 3.12, 3.14, 3.24
Y: p45 : 48, 53
Preview: The second law of thermodynamics
A: 4.1-4.4
Y:2.1-2.6
Practice 1: Calculation of work
1. A water bubble is expanded from a radius of 1.00cm to
3.25cm. The surface tension of water is 71.99N.m-1.

104 m 2
w    d  2 4 (r  ri )  8  71.99 N .m (3.25 cm 1.00 cm ) 
cm 2
 1.73J
2
f

2
1
2
2
2
2
2. A current of 3.20 A is passed through a heating coil
for 30.0s.The electrical potential across the resistor is
14.5 V. The work done on the coil.
w   dQ  Q  It  14.5V  3.20 A  30.0s  1.39kJ

3. If the force to stretch a fiber a distance x is given by
F=-kx with k=100 N.cm-1, how much work does it take
to stretch the fiber 0.15cm?
kx2 xf
100.0 N .m1  x 2 0.15
w   F .dl   kxdx  [
]x 0  [
]0  1.1J
2
2
x0
xf
Practice 2: Calculate △U and △H


(1) 1.00 mol of H2O goes from 25.0℃ and 1.00 atm to 30.0
℃and 1.00 atm. (density 0.9956 g.cm-3 and 0.9970 g.cm-3)
△U=Q+W
W=-P. △V=-0.0024J
Q=75.295J. mol-1.K-1×5×1.0=376.475J
T2
U 
 C dT
V
T1
(2) 1.0 mol CaCO3 change in the form of calcite converts to
aragonite. The density of the solids are 2.71 g.cm-3 and 2.93 g.cm-3.
ΔH=ΔU+Δ(PV)
PΔV=-0.3J
ΔU=210J
ΔU≈ΔH
Discussions next class: Application of the
first law

Group 1: Understanding about the atmosphere and
climate phenomenon
(1) Marine climate/ Continental climate
(2) Altitude/temperature

Group 2: Is it possible water being used as fuel?

Group 3: Food and energy reserves.


Energy content and availability of the
major food components
percent
availabi
lity
92
type of food
food
ΔH°,
kJ g–1
Protein
meat
22.4
egg
23.4
butter
38.2
animal fat
39.2
starch
17.2
glucose
(sugar)
15.5
99
ethanol
29.7
100
Fat
Carbohydrate
95
Energy densities of some common fuels
fuel
MJ kg–1
wood (dry)
15
coal (poor)
15
coal (premium)
27
ethanola
30
petroleum-derived products
45
methane, liquified natural gas 54
hydrogenb