Q.The Enthalpy of formation of co² and h²o is -393 is mol and -285kJ/mol respectively.calculate the enthalpy of compustion of exhane it the enthalpy of of formation of exhane is -537KJ/mol .
Answers
Answer:
-2.21kj
Explanation:
Given,
H
2
+
2
1
O
2
⟶H2O(l); ΔH=−285.85kJmol
−1
...( i)
C+O
2
⟶CO
2
(g); ΔH=−293.7kJmol
−1
..( ii)
∴ 1g starch on combustion gives 17.49 kJ energy.
∴ 162 n g starch on combustion gives =17.49×162nkJenergy
=2833.38nkJ
Molar mass of starch (C
6
H
10
O
5
)
n
=162n
Therefore,
(C
6
H
10
O
5
)
n
+6nO
2
⟶6nCO
2
+5nH
2
O; ΔH=−2833.38nkJ ...( iii)
Multiply eq. (ii) by 6n and eq. (i) by 5n. then add
5nH
2
+
2
5n
O
2
+6nC+6nO
2
⟶5nH
2
O+6nCO
2
; ΔH=−3191.45nkJ ...( iv)
Subtract eq. (iii) from eq. (iv):
6nC+5nH
2
+
2
5n
O
2
⟶(C
6
H
10
O
5
)
n
; ΔH=−358.07nkJ
∴ Heat of formation for 162n g starch =−358.07nkJ
∴ Heat of formation for 1 g starch =
162n
358.07n
=−2.21kJ