Enthalpy of Reaction and Hess’ Law
1.
Worksheet 2
The enthalpies of these reactions at 25°C are given in kJ.
H° in kJ mol-1
C4H9OH (l) + 6 O2 (g)
 4 CO2 (g) + 5 H2O (g)
-2456
(C 2H5)2O (l) + 6 O2 (g)
 4 CO2 (g) + 5 H2O (g)
- 2510
From a consideration of the above information, calculate the change in enthalpy for
C4H9OH (l) > (C 2H5)2O (l)
2.
The enthalpies of three reactions at 25°C are given in kJ.
H° in kJ mol-1
2 H2 (g) ) + O2 (g)  2 H2O (l)
- 572
2 C2H6 (g) + 7 O2 (g)  4 CO2 (g) + 6 H2O (l)
C2H4 (g) + 3 O2 (g) )  2 CO2 (g) + 2 H2O (l)
Use this information to calculate the change in enthalpy for
C2H6 (g) (g)

C2H4 (g) + H2 (g)
Is the reaction endothermic or exothermic? Explain.
3.
- 3120
- 1411
The enthalpies of three reactions at 25°C are given in kJ.
DH° in kJ mol-1
Mg (s) + 1/2 O2 (g)  MgO (s)
-601.7
C(s) + O2 (g)
 CO2 (g)
-393.5
Mg (s) + C (s)) + 3/2 O2 (g)  Mg CO3 (g)
-1095.8
Use this information to calculate the change in enthalpy for
MgO (s) + CO2 (g) MgCO3 (s)
4.
The enthalpies of three reactions at 25°C are given in kJ.
DH° in kJ mol-1
C(s) + 1/2 O2 (g)  CO (g)
C(s) + O2 (g)
 CO2 (g)
CO (g) + 1/2 O2 (g)  CO2 (g)
H2 (g) ) + 1/2 O2 (g) H2O (g)
-241.8
Use this information to calculate the change in enthalpy for
C(s) + H2O (g)  CO (g) + H2 (g)
5.
- 110.5
- 393.5
-283.0
The enthalpies of three reactions at 25°C are given in kJ.
H° in kJ mol-1
N2 (g) + 2O2 (g)  2 NO2 (g)
+ 33.2
2 NO (g) + O2 (g)  2 NO2 (g)
- 57.1
From a consideration of the above information, calculate the change in enthalpy for
N2 (g) + O2 (g)  2 NO (g)