Part A What is ? H ? rxn for the following chemical reaction? C S 2 (g)+2 H 2 O(
ID: 820045 • Letter: P
Question
Part A
What is
?
H
?
rxn
for the following chemical reaction?
C
S
2
(g)+2
H
2
O(l)?C
O
2
(g)+2
H
2
S(g)
You can use the following table of standard heats of formation
(?
H
?
f
)
to calculate the enthalpy of the given reaction.
Element/ Compound
Standard Heat of Formation (kJ/mol)
Element/ Compound
Standard Heat of Formation (kJ/mol)
H(g)
218
N(g)
473
H
2
(g)
0
O
2
(g)
0
H
2
O(l)
?285.8
O(g)
249
C
S
2
(g)
116.7
H
2
S(g)
?20.60kJ
C(g)
71
C
O
2
(g)
?393.5kJ
C(s)
0
HN
O
3
(aq)
?206.6
Express the standard enthalpy of reaction to three significant figures and include the appropriate units.
Element/ Compound
Standard Heat of Formation (kJ/mol)
Element/ Compound
Standard Heat of Formation (kJ/mol)
H(g)
218
N(g)
473
H
2
(g)
0
O
2
(g)
0
H
2
O(l)
?285.8
O(g)
249
C
S
2
(g)
116.7
H
2
S(g)
?20.60kJ
C(g)
71
C
O
2
(g)
?393.5kJ
C(s)
0
HN
O
3
(aq)
?206.6
Explanation / Answer
first, switch the first rxn around...
SO2 + H2O--> H2S + 3/2 02 new DHrxn = +563kJ
then multiply it by two
2 SO2 + 2 H2O --> 2 H2S + 3 02 DHrxn = 1126kJ
then combine the two reactions, canceling as necessary
2 SO2 + 2 H2O --> 2 H2S + 3 02 DHrxn = 1126kJ
CS2 + 3 O2 --> CO2 + 2 SO2 DHrxn = -1075kJ
(the 2 SO2 and 3 O2 will be canceled out)
so you're left with:
CS2 + 2 H20 --> 2 H2S + CO2
therefore DHrxn = 1126 + -1075 = 51kJ