Chemistry exercise from Masterton book

1. 1.Table 8.2, write thermochemical equations for saving.
a. benzene boiling c. Napthalene melting
b. bromine freezing
answer :
a. C6H6(l) → C6H6(g) ; H = 30,8 kJ
b. Br2 (l) → Br2(s) ; H = -10,8 kJ
c. C10H8 (s) → C10H8(l) ; H = 19,3 Kj
3. Chemical equations for the formation of one mole growing compounds from the elements in
Their state at 25oC and 1 atm
a. Aluminium oxide (s)
b. Carbon Tetracloride (l)
c. Sodium Sulfate (s)
d. Potassium dichromate (s)
Answer :
a. 2Al (s) + ½ O2 (g) → Al2O (s)
b. C (g) + 2Cl2 (g) → CCl4 (g)
c. 2Na (s) + 1/8S8 (s) + 2O2 → Na2SO4(s)
d. 2K (s) + 2 Cr (s) + 2O2(g) → K2Cr2O4 (s)
5. The Specific heat of solid aluminium is 0,902 J/goC. The ammount of heat that must be
absorbed to raise temperature of a 4,75 g aluminium sample form of 25,0oC.
Known :
Cp = 0,902 J/goC.
m = 4,75 gr
T aluminium = 26,8 o C
Question : the value of Q......?
Answer :
T = T2 – T1
= 26,8 o C – 25,0 o C
= 1,8 o C
Q = m x Cp x T

2. = 4,75 gr x 0,902 J/go C x 1,8 o C
= 7,7121 J
7. It is found that 252 Joule of heat must be absorbed to raise temperature of 50,0 gr of nickel
from 20,0 to 31,4 o C. What specific heat of nickel?
Known :
Q = 252 Joule
m = 50,0 gr
T2 = 31, 4 o C
T1 = 20,0 o C
Question : the value of Cp........... ?
Answer :
T = T2 – T1
= 31,4 o C – 20,0 o C
= 11,4 o C
Q = m x Cp x T
Cp = Q / m x T = 252 / 50 x 11,4 = 252 / 570 = 0,44 J/g o C
9. When 2.80 g of Calcium chloride dissolves in 100,0 g and the temperature of water rises
from 20,50 to 26, 40 o C. ( Heat = 4,18 J/g o C )
a. write a balanced equation for the solution process
b. What is q for the process described ?
c. Is the solution process exothermic or endothermic
d. How much heat is absorbed by the water if one mole of calcium chloride is dissolved ?
Answer
a.
b. q = m x c x T
= 100 X 4,18 X 4,90
= 2,048 KJ
C. Endoterm

3. 11. A sample of sucrose, C12H22O11 weighing 4,50 g is burned in a bomb calorimeter. The heat
capacity of calorimeter is 2,411x104
J/o
C. The temperature rises from 22,15 to 25,22o
C.
Calculate q for the combustion of one mole of sucrose.
Known: m= 4,50 g = 4,5x10-3
Kg mol=
Mr
massa
C= 2,411x104
J/o
C = molg /342
g4,50
=0,00132 mol
∆T= 25,22o
C - 22,15o
C= 3,07o
C Question: q=….?
Answer: Q=C ∆T
= 2,411x104
x 3,07
=7,4018 J (for 1kg of sample)
for 4,5x10-3
Kg of sample = 4,5x10-3
x7,4018
=0,033 J
for 1 mol of sample = mole
mole
00132,0
1
x 0,033 J
= 25 J
13. When 1,750 g of methane, CH4, burns in a bomb calorimeter, The temperature in the bomb
rises 3,293o
C. under this conditions, 885,3kJ of heat is evolved per mole methane burned.
Calculate the calorimeter heat capacity in J/o
C
Known : m= 1,750 g molg /16
g1,750
=0. 109 mole
∆T= 3,293o
C
Q= 885,3kJ (for 1 mole of sample)
Question: C=….?
Answer: Q for 0. 109 mole CH4 =0,109 x 885,3kJ

4. =96,498 kJ
Q=C ∆T
96,498 = C x 3,293
C= 293,3
96,498
=29,3 J/o
C
15. A 0,2500-g sample of naphthalene, C10H8, is burned in a bomb calorimeter, heat capacity =
4999 J/o
C. if the bomb is initially atb20,00o
C, what is the final temperature of the system?
(When one mole of naphthalene burns, 5,15 x 103
kJ of heat are evolved.)
Known : m=0,2500 g
C= 4999 J/o
C
T1=20,00o
C
Q=5,15 x 103
kJ (for 1 mole of sample)
Question : T2=…?
Answer : Q=5,15 x 103
kJ (for 1 mole of sample) mol=
Mr
massa
=
molegr
gr
/128
2500,0
=0,00195
mole
For 0,00195 mole of example
=0,00195 x 5,15 x 103
kJ
=10,06 kJ
Q=C ∆T
10,06=4999 x (T2-20,00)
T2=0,002+20,00
=20,002o
C

5. 17. when 1,00g of acetylene, C2H2(g), burns in a bomb calorimeter, the temperature rises 10,94o
C.
in a separate experiment, it is found that when 8,16kJ of heat is added to the calorimeter,
the temperature increases by 1,7o
C. Calculate:
a. The heat capacity of calorimeter
b. q for the combustion of one gram of acetylene
c. q for the combustion of one mole of acetylene
Known: when m= 1,00g , so ∆T= 10,94o
C
When Q= 8,16kJ=8160J, so ∆T=1,7o
C
Question: a. C=…?
b. Q for acetylene 1 gram
c. Q for acetylene 1mole
Answer: a. Q=C ∆T b. Q=C ∆T
8160J = C x 1,7 =4800 x 10,94
C=
7,1
8160
=52512 J
C=4800 J/o
C
c. mass of 1 mole acetylene Q for acetylene 1 gram
=mole x Mr =
gr
g
1
26
x 52512 J
=1 mole x 26 gr/Mr =1365313J =1365,313KJ
= 26gr
19. The combustion of one mole enzene, C6H6(l), in oxygen liberates 3,268 x 103
kL of heat. The
products of reacions are carbon dioxide and water.

6. a.write the thermochemical equation for the combustion of benzene.
b. is the reaction exothermic or endothermic?
c. draw the diagram. Similar to figure 8.4, for this reaction.
d. calculate ∆ H when 10,00g of benzene is burned.
e. How many grams of benzene must be burned to evolve one kilojoule of heat?
21. Consider the dissociation of water into ions
H2O(l) → H+
(aq) +OH-
(aq) ∆ H= 55,8 KJ
a. Calculate ∆ H when one mole of water is formed from the ions.
b. What is ∆ H when 1,00g of water is formed?
Answer: a. ∆ H= -55,8 KJ
c. 1,00g H2O =
moleg
g
/18
00,1
=0,056 mole
So, ∆ H=
mole
mole
1
056,0
x -55,8 KJ
=-3,1 KJ
23. When ignited, ammonium dichromate decomposes in a fiery display. This is the reaction for
the “laboratory volcanoes often demonstrated in science fair projects. The decomposition of
1,000g of ammonium dichromate produce 1,19kJ energy. Nitrogen gas, steam, and
chromium(III) oxide.
a. write the balanced thermochemical equation for the reaction.
b. what is ∆ H for the formation of 11,2 L of nitrogen at 0o
C and 1,00 at atm?
Known: m= 1,000g

7. 25. A typical fat in the body is gliceryl trioleat (C57H104O6). When it is metabolized in the body, it
combines with oxygen to produce carbon dioxide, water, and 3,022 x 104
KJ of heat per mole of
fat. a. Write a balanced thermochemical equation for the metabolism of fat.
b. how many grams of fat would have to be burned to heat one liter of water (d=
1,00g/mL) from 25,00o
C to 30o
? the specific heat of water is 4,18
Answer :
a. C57H104O6 + 80 O2 → 57 CO2 + 52 H2O H = 3,022 X 10 -4
27. Which requires the absorption of a greater amount of heat, melting 100,0 g of naphthalene or
boiling 100 g of water. Use Table 8.2.
29. Which envolves more heat, the freezing of 25,0 g of mercury or the condensation of 100,0 g
of benzene vapor? Use table 8.2.