Chemistry 3411 Solutions Worksheet - Georgia Institute Of Technology - 2010
ADVERTISEMENT
1
2
3
4
5
6
7
8
9
10
11
12CHEM 3411, Fall 2010
Solution Set 2
In this solution set, an underline is used to show the last significant digit of numbers. For instance in
x = 2.51693
the 2,5,1, and 6 are all significant. Digits to the right of the underlined digit, the 9 & 3 in the example, are not
significant and would be rounded off at the end of calculations. Carrying these extra digits for intermediate values in
calculations reduces rounding errors and ensures we get the same answer regardless of the order of arithmetic steps.
Numbers without underlines (including final answers) are shown with the proper number of sig figs.
1
Exercise 2.19a pg 86
Given
◦
1
The standard enthalpy of combustion of cyclopropane is
2091 kJ mol
at 25
C. Additionally, the enthalpy of
1
formation of its isomer propene is +20.42 kJ mol
.
In terms of given variables, this is written:
⊖
1
∆
H
=
2091 kJ mol
cyclopropane combustion
r
⊖
1
∆
H
= +20.42 kJ mol
propene enthalpy of formation
f
Find
Calculate . . .
• (a) The enthalpy of formation of cyclopropane
• (b) The enthalpy of isomerization from cyclopropane to propene
Strategy
We begin by constructing the balanced chemical equation for combustion of cyclopropane
⊖
(g) → 6H
= 2 × 2091 kJ mol
1
2C
H
+ 9O
O(l) + 6CO
(g)
∆
H
3
6
2
2
2
r
For any such reaction the reaction enthalpy can related to the enthalpy of products and reactants by (Equation 2.32
on pg 68 in your text book)
∑
∑
⊖
⊖
⊖
∆
H
=
ν
∆
H
ν
∆
H
r
p
f
r
f
p
r
Products
Reactants
which for this reaction is
⊖
⊖
⊖
⊖
⊖
∆
H
= 6∆
H
(H
O(l)) + 6∆
H
(CO
(g))
2∆
H
(C
H
) + 9∆
H
(O
(g))
r
f
2
f
2
f
3
6
f
2
reactants
products
⊖
⊖
Using the fact that the standard state of oxygen is O
(g) (∆
H
(O
(g)) = 0) the following expression for ∆
H
(C
H
)
2
f
2
f
3
6
is obtained through rearrangement
1
ADVERTISEMENT
0 votes
Related Articles
Related forms
Related Categories
Parent category: Education