Section 1.1 Section 1.2 Section 1.3 - The Student Room

SECTION 4
6 a
H
H
H
H
b
H 3 C
H 3 C
C
C C
* H C C
H H
CH 3
H 3 C
C
C C
* H C C
H
CH 3
H 3 C
CH
CH 3
H
C
H
C
C
H
C
H
C
C
H
H
H
H
H
O
limonene
carvone
c
No: the carbon which was chiral is
now bonded in the same way in both
directions around the ring.
Section 4.1
1 a Standard enthalpy change of combustion is the
enthalpy change when 1 mole of the compound is
burnt completely in oxygen, under standard
conditions (ie the compound and the products in their
most stable states at 1 atmosphere pressure and at a
stated temperature, often 298 K).
b Standard enthalpy change of formation is the
enthalpy change when 1 mole of a compound is
formed from its elements, with both the compound
and its elements being in their standard states (ie their
most stable state at 1 atmosphere pressure and at a
stated temperature, often 298 K).
2 The formation of a compound from its elements may be
an exothermic reaction (DH f
negative) or an
endothermic reaction (DH f
positive). However, energy is
liberated whenever a substance burns, so combustion
reactions are always exothermic (DH c
negative).
3
Enthalpy
1
1
2 H 2 (g) + 2 Cl 2 (g)
DH = –92.3 kJ mol –1
HCl(g)
Progress of reaction
e 6C(s) + 6H 2
(g) + 3O 2
(g) Æ C 6
H 12
O 6
(s)
f C 6
H 12
O 6
(s) + 6O 2
(g) Æ 6CO 2
(g) + 6H 2
O(l)
5 DH c
!(C) is enthalpy change when 1 mole of carbon
burned completely under standard conditions, ie
C(s) + O 2
(g) Æ CO 2
(g)
DH f
!(CO 2
) is enthalpy change when 1 mole of carbon
dioxide is formed from its elements with both the carbon
dioxide and its constituent elements in their standard
states, ie
C(s) + O 2
(g) Æ CO 2
(g)
6 a Thermometer, measuring cylinder, gas meter.
b Volume of water used, temperature rise of water,
volume of gas used.
c Cooling losses, impurity of the gas, etc.
7 a DH = –667 kJ mol –1
b Much heat was lost to the surroundings in the
experiment whereas the accurate DH value in the data
book would have been determined using a calorimeter
in which very little heat is lost.
8 a M r
(C 7
H 16
) = 100
b i 481.7 kJ released ii 481 700 kJ released
(Assumed combustion is complete and CO 2
and H 2
O
are the only products. Also, that combustion is carried
out under standard conditions.)
c Density of heptane
9 a H 2
(g) + O 2
(g) Æ H 2
O(l)
b DH f,
! 298
(H 2
O) = –286 kJ mol –1
c –143 kJ (assuming combustion takes place under
standard conditions)
d +286 kJ mol –1
Enthalpy
1
1
2
2 H 2 (g) + I 2 (s)
HI(g)
DH = +26.5 kJ mol –1
Progress of reaction
10 a Enthalpy change of formation of propane.
b Enthalpy change of combustion of 3 moles of carbon
and 4 moles of hydrogen.
c Enthalpy change of combustion of propane.
d DH 1
+ DH 3
= DH 2
e DH 1
= DH 2
– DH 3
= 3(–393) kJ mol –1 + 4(–286) kJ mol –1
– (–2220) kJ mol –1
= –103 kJ mol –1
11 a 4C(s) + 5H 2
(g) Æ C 4
H 10
(g)
b
DH
4C(s) + 5H 2
(g)
1
C 4
H 10
(g)
4 a 2C(s) + 3H 2
(g) + O 2
(g) Æ C 2
H 5
OH(l)
b C 2
H 5
OH(l) + 3O 2
(g) Æ 2CO 2
(g) + 3H 2
O(l)
c 4C(s) + 5H 2
(g) Æ C 4
H 10
(g)
d C 4
H 10
(g) + 6 O 2
(g) Æ 4CO 2
(g) + 5H 2
O(l)
+ 6 O 2
(g) DH 2
DH 3
+ 6 O 2
(g)
4CO 2
(g) + 5H 2
O(l)
169