Enthalpy Of Reaction And Calorimetry Worksheet Page 17
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20Thermochemistry Review Problems
1. A 2.50 g sample of sucrose (C 12 H 22 O 11 ) was burned in excess oxygen under a 60.0 g Al calorimeter
which contained 2.19 kg of water. The temperature of the water increased from 20.5 °C to 25.0 °C.
Determine the molar heat of combustion of sucrose.
a) Calculate the enthalpy change, H rxn , for the following reaction using equations 1, 2 and 3.
2.
FeO
+
CO
Fe
+
CO 2
H rxn (kJ)
Given:
1)
Fe 2 O 3
+
3 CO
2 Fe
+
3 CO 2
-25
2) 3 Fe 2 O 3
+
CO
2 Fe 3 O 4
+
CO 2
-47
3)
Fe 3 O 4
+
CO
3 FeO
+
CO 2
+38
b) Calculate the enthalpy change, H rxn , for the above using equations of formation and H f .
c) Using the Summation Formulas, calculate the H rxn , S rxn , G rxn and determine the temperature
where this reaction is spontaneous.
3. a) Calculate the enthalpy change, H rxn , for the following using formation equations and H f .
4 ClF 3 (g)
3 N 2 H 4 (g)
+
3 N 2 (g) +
12 HF (g)
+
2 Cl 2 (g)
H f ( ClF 3 ) = −158.87 kJ/mol
b) Predict the sign of ∆Srxn and ∆Grxn.
4. Calculate the enthalpy change, H rxn , for the following reaction using equations 1, 2 and 3.
2 H 3 BO 3
B 2 O 3
+
3 H 2 O
H rxn (kJ)
Given:
1)
H 3 BO 3
HBO 2
+ H 2 O
-0.0200
+ H 2 O
2) 2 B 2 O 3
H 2 B 4 O 7
-17.5
H 2 B 4 O 7 + H 2 O 4 HBO 2
3)
-11.3
5. Using the average bond energies, NN (941 kJ/mol), N=N (418 kJ/mol), N-N (160 kJ/mol), N-H (391
kJ/mol) and H-H (432 kJ/mol) estimate the H f for hydrazine, N 2 H 4 .
6. The H rxn of the gaseous reaction:
XeF 2
+
H 2
2 HF
+
Xe
is found to be –430 kJ. Use this value and average bond energies [H-F (565 kJ/mol)] to determine the
average bond energy of the Xe-F bond.
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