KIMIA TINGKATAN 5
(Nota 11)
BAB 3 - TERMOKIMIA
Latihan Tambahan
1.
Apabila 50 cm3 larutan plumbum(II) nitrat 2.0 mol dm−3, Pb(NO)3)2 dicampurkan kepada 50 cm3 larutan
kalium sulfat, K2SO4 2.0 mol dm−3, kenaikan suhu ialah 10 °C.
Berapakah kenaikan suhu jika:
(a) 100 cm3 larutan plumbum(II) nitrat 2.0 mol dm−3, Pb(NO)3)2 dicampurkan kepada 100 cm3 larutan kalium
sulfat, K2SO4 2.0 mol dm−3
(b) 50 cm3 larutan plumbum(II) nitrat 1.0 mol dm−3, Pb(NO)3)2 dicampurkan kepada 50 cm3 larutan kalium
sulfat, K2SO4 1.0 mol dm−3
(c) 50 cm3 larutan plumbum(II) nitrat 2.0 mol dm−3, Pb(NO)3)2 dicampurkan kepada 50 cm3 larutan kalium
sulfat, K2SO4 1.0 mol dm−3
(d) Apakah kesimpulan yang dapat anda deduksikan tentang corak perubahan suhu dan tentukan faktor
yang mempengaruhi perubahan suhu campuran apabila isi padu atau kepekatan larutan yang berlainan
digunakan?
2.
Persamaan termokimia bagi pembakaran lengkap etanol, C2H5OH ditunjukkan di bawah:
C2H5OH(ce) + 3O2(g) → 2CO2(g) + 3H2O(ce); ΔH = -1376 kJ mol−1
100
90
80
Serbuk magnesium
70
Rajah 1 menunjukkan susunan radas bagi menentukan
haba penyesaran di antara 100 cm3 larutan kuprum(II) nitrat
0.5 mol dm−3 dengan serbuk magnesium berlebihan.
50
60
3.
110
Hitungkan jisim etanol yang diperlukan untuk membakar dengan lengkap dalam oksigen berlebihan supaya
menaikkan suhu 200 cm3 air sebanyak 50.0 °C. Anggapkan tidak ada haba yang hilang ke persekitaran,
[Jisim molar etanol = 46 g mol−1]
–10
0
10
20
30
40
Jadual 1 menunjukkan keputusan eksperimen itu.
Jadual 1
Suhu awal larutan kuprum (II) nitrat
28 °C
Suhu tertinggi campuran
X °C
Larutan kuprum
(II) nitrat
Rajah 1
(a) Nyatakan maksud haba penyesaran.
(b) (i) Susunan radas yang digunakan dalam eksperimen di atas tidak boleh mengatasi kadar kehilangan haba
ke persekitaran. Cadangkan alat radas yang sesuai untuk mengatasi masalah tersebut.
(ii) Selain daripada perubahan suhu, nyatakan satu pemerhatian lain bagi eksperimen ini.
(c) Jika serbuk magnesium digantikan dengan serbuk argentum di dalam eksperimen ini, ramalkan perubahan
haba dan berikan sebab bagi jawapan anda. (d) Jika haba penyesaran bagi eksperimen di atas ialah -42 kJ mol−1.
(i) Tentukan suhu tertinggi bagi X.
[Muatan haba tentu bagi larutan, c = 4.2 J g−1 °C−1, Ketumpatan larutan = 1 g cm−3]
(ii) Hitung jisim magnesium yang bertindak balas lengkap apabila 100 cm3 larutan kuprum(II) nitrat
0.5 mol dm−3 digunakan.
[Jisim atom relatif : Mg = 24]
4.
Rajah 2 menunjukkan susunan radas untuk menjalankan satu eksperimen bagi menentukan haba pembakaran
suatu hidrokarbon cecair, X.
50
60
70
80
90
100
110
Termometer
Pengadang
angin
0
10
20
30
40
Bekas
–10
Pengadang
angin
Air
Tungku kaki
tiga
Kasa dawai
Pelita
Cecair X
Bongkah kayu
Rajah 2
(a) (i) Kenal pasti dua kesalahan dalam susunan radas pada Rajah 5 dan nyatakan bagaimana kesilapan itu
dibetulkan.
(ii) Selepas kesilapan dibetulkan, eksperimen boleh dijalankan.
Hitungkan haba yang dibebaskan apabila suhu air itu meningkat sebanyak 30 °C.
[Muatan haba tentu air = 4.2 J g−1 °C−1, ketumpatan air = 1 g cm−3]
(iii) 1.72 g X telah terbakar untuk menaikkan suhu air sebanyak 30 °C. Hitungkan haba pembakaran bagi
cecair X.
[Jiism molar bagi X = 86 g mol−1]
(b) Jadual 2 menunjukkan jisim molekul relatif dan haba pembakaran bagi dua alkohol.
Jadual 2
Alkohol
Etanol
Jisim molekul relatif
46
Haba pembakaran / kJ mol−1
-1376
Butan-1-ol
74
-2675
Hitungkan nilai bahan api bagi dua alkohol tersebut.
Berdasarkan jawapan anda, nyatakan bahan api yang lebih efisien.
CHEMISTRY FORM 5
(Note 11)
CHAPTER 3 - THERMOCHEMISTRY
Additional Exercises
1.
When 50 cm3 of 2.0 mol dm−3 lead (II) nitrate, Pb(NO)3)2 solution is mixed with 50 cm3 of 2.0 mol dm−3
potassium sulphate, K2SO4 solution, the temperature rise is 10.0 °C.
How much is the temperature increase if:
(a) 100 cm3 of 2.0 mol dm−3 lead(II) nitrate, Pb(NO)3)2 solution is mixed with 100 cm3 of 2.0 mol dm−3
potassium sulphate, K2SO4 solution
(b) 50 cm3 of 2.0 mol dm−3 lead(II) nitrate, Pb(NO)3)2 solution is mixed with 50 cm3 of 2.0 mol dm−3 potassium
sulphate, K2SO4 solution
(c) 50 cm3 of 2.0 mol dm−3 lead(II) nitrate, Pb(NO)3)2 solution is mixed with 50 cm3 of 1.0 mol dm−3 potassium
sulphate, K2SO4 solution
(d) What conclusions can you draw from the pattern of temperature change and determine the factors
influencing the change in temperature of the mixture when different volumes or concentrations of the
solutions are used?
Calculate the mass of ethanol needed to completely burn in excess oxygen in order to raise the temperature of
200 cm3 of water by 50.0 °C. Assume no heat is lost to the environment,
[Molar mass of ethanol = 46 g mol−1]
3.
Figure 1 shows the apparatus set-up to determine the heat of displacement
of 100 cm3 of 0.5 mol dm−3 copper(II) nitrate solution
with excess magnesium powder.
Magnesium powder
40
50
60
70
80
90
100
110
2.
–10
0
10
20
30
Table 1 below shows the result from the experiment.
Copper(II) nitrate
Table 1
Initial temperature of copper (II) nitrate solution
28 °C
Highest temperature of the mixture
X °C
Figure 1
(a) State the meaning of heat of displacement.
(b) (i) The set-up of the apparatus used in the experiment above cannot be used to reduce the rate of heat loss
to the surroundings. Suggest a suitable apparatus to solve this problem.
(ii) Besides the change in temperature, state another observation of this experiment.
(c) If the magnesium powder is replaced by silver powder in this experiment, predict the heat change and give a
reason. (d) If the heat of displacement of the experiment above is -42 kJ mol−1,
(i) determine the highest temperature of X.
[Specific heat capacity of solution, c = 4.2 J g−1 °C−1; density of solution = 1 g cm−3]
(ii) calculate the mass of magnesium that reacts completely when 100 cm3 of 0.5 mol dm−3 copper(II) nitrate solution is used.
[Relative atomic mass : Mg = 24]
4.
Figure 2 shows the set-up of the apparatus used to carry out an experiment to determine the heat of combustion
of a liquid hydrocarbon, X.
50
60
70
80
90
100
110
Thermometer
Wind shield
20
30
40
Beaker
–10
0
10
Wind shield
Wire gauze
Spirit lamp
Water
Tripod stand
Liquid X
Wooden block
Figure 2
(a) (i)
(ii)
(iii)
Identify two mistakes in the set-up of apparatus in Figure 2 and state how the mistakes can be corrected.
After the mistakes are corrected, the experiment can be carried out.
Calculate the heat released when the temperature of the water increases by 30 °C.
[Specific heat capacity of water = 4.2 J g−1 °C−1; density of water = 1 g cm−3]
1.72 g of X was burnt to raise the temperature of the water by 30 °C. Calculate the heat of combustion
of X.
[Molar mass of X = 86 g mol−1]
(b) Table 2 shows the relative molecular mass and heat of combustion of two alcohols.
Table 2
Alcohol
Ethanol
Relative molecular mass
46
Heat of combustion / kJ mol−1
-1376
Butan-1-ol
74
-2675
Calculate the fuel value for the two alcohols.
Based on your answer, state which fuel is more efficient.