Calculate the formation of propane C3H8 if its enthalpy of combustion -2280kjmol-4 . Given enthalpy of formation of CO2 and H2O are -393. 5 and -286. 1kjmol-1 respectively?
Answers
Answer:
You know that propane undergoes combustion as described by the balanced chemical equation
C
3
H
8
(
g
)
+
5
O
2
(
g
)
→
3
CO
2
(
g
)
+
4
H
2
O
(
l
)
You also know that when
2.5000 g
of propane undergo combustion, the reaction gives off
115.75 kJ
of heat.
Now, in order to find the enthalpy change of combustion of propane,
Δ
H
comb
, in kilojoules per mole, you need to figure out how much heat is released when
1
mole of propane undergoes combustion.
Use the molar mass of propane to convert the mass of the sample to moles
2.5000
g
⋅
1 mole C
3
H
8
44.1
g
=
0.0566893 moles C
3
H
8
SInce you know that when
0.0566893
moles of propane undergo combustion,
115.75 kJ
of heat are being released, you can say that when
1
mole of propane undergoes combustion, the reaction will give off
1
mole C
3
H
8
⋅
115.75 kJ
0.0566893
moles C
3
H
8
=
2041.8 kJ
This means that the enthalpy change of combustion of propane will be
Δ
H
comb
=
−
2041.8 kJ
−−−−−−−−−−−−−−−−−−−−
The minus sign is used to symbolize heat given off.
SIDE NOTE The difference between this value and what you have at option (E) is most likely caused by the value used for the molar mass of propane.
Explanation:
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