CHEM 241
Chemistry Department, Science Faculty of girls
King AbdulAziz University
CHAPTER III Assignments
Student name:
ID No.:
_
1. Calculate the standard enthalpy of formation of N2O5(g) at 25 oC on the basis of the following
equations:
2NO (g)  O 2(g)  2NO 2(g)
H o  114.1 kJmol 1
4NO (g)  O 2(g)  2N 2 O 5(g)
H o  110.2 kJmol 1
N 2 (g)  O 2 (g)  2NO (g)
H o  180.5 kJmol 1
Solution:
A 10.0 g sample of a metal at 78.0 oC is submerged in 50.0 mL of water at 25.0 oC, the final
temperature of the water is measured to be 26.1 oC. Assuming no heat is lost to the surroundings,
what is the specific heat capacity of the metal? Ĉ water  4.184 J.g-1 oC 1 . (Ans. 0.44 J.g-1 o C 1 )
Solution:
i
2. 20.0 g pice of metal at 100 oC is placed in a calorimeter containing 50.7 g of water at 22.0 oC.
The final temperature of the mixture is 25.7 oC. What is the specific heat of the metal?
-1 o 1
Ĉ water  4.184 J.g C .
3. Solution:
4. A 21.8 g sample of ethanol (C2H5OH) is burned in a bomb calorimeter. If the temperature rise from 25.0
o
C to 62.3 oC, determine the heat capacity of the calorimeter. The molar mass of ethanol is 46.07 g.mol-1.
(Ans. 15.7 kJ.oC-1)
Solution:
5. How much energy is released during the formation of 98.7 g of Fe, according to the reaction
below? (Ans. 753 kJ)
Solution:
ii
6. Using the following information, what mass of HF must react in order to produce 345 kJ of
energy? Assume excess SiO2. (Ans. 1.5×102 g)
Solution:
7. Consider the reaction
CH 3OH (l )  CH 4 ( g )  1/ 2O2( g )
(a) Calculate H 2o9 8
o
(b) Estimate E 2 9 8
(c) Write an equation that would allow you to obtain H o at 500 oC and 1 atm.
Solution:
8. If glycine reacts with HNO2 at 25 oC according to the following equation
NH3CH 2 COOH(aq)  HNO2(aq)  HOCH2 COOH(aq)  N 2(g)  H 2 O (l ) . Calculate H o  E o ?
Solution:
3
9. An ice cube weighing 18 g is removed from a freezer, where it has been at -20 oC.
(a) How much heat is required to warm it to 0 oC without melting it?
(b) How much additional heat is required to melt it to liquid water at 0 oC?
Solution:
10. Liquid water is vaporized at 100 oC and 1 atm. The heat of vaporization is 40.67kJ mol-1. What
are the values of (a) Wrev /mol, (b) q /mol, (c) E /mol and (d) H /mol.
Solution:
4