10. Given the following thermochemical equation, calculate the heat involved in decomposing 12.5 g of water to the elements. 2H2(g) + O2(g) → 2H2O(I) AH= -571.6 kJ (Molar mass of water = 18 g) A. +397 kJ B. -397 kJ C. -198 kJ (d) +198 kJ
10. Given the following thermochemical equation, calculate the heat involved in decomposing 12.5 g of water to the elements. 2H2(g) + O2(g) → 2H2O(I) AH= -571.6 kJ (Molar mass of water = 18 g) A. +397 kJ B. -397 kJ C. -198 kJ (d) +198 kJ
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Chapter6: Thermochemisty
Section: Chapter Questions
Problem 6.132QP
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Concept explainers
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Question
![10. Given the following thermochemical equation, calculate the heat involved in decomposing 12.5 g of water to
the elements. 2H2(g) + O2(g) → 2H2O(I) AH=-571.6 kJ
(Molar mass of water = 18 g)
A. +397 kJ
В. -397 kJ
C. -198 kJ
(d) +198 kJ
11. The table below shows the energy released when burning 1.0 g of each of the following organic compounds.
Compound
Energy released / kJg'
Relative molecular mass
Methane
55.7
16
Ethanol
29.8
46
Propanol
33.6
60
Octane
48.4
114
The standard enthalpy change of combustion of one of the above compounds is -2-016 kJmol-'. What is this
organic compound?
A. Methane
B. Ethanol
C. Propanol
D. Octane
12. The thermochemical equation shown below refers to the combustion of ammonia.
AH°. =x kJ
4NH3(g) + 302(g) → 2N2(g) + 6H,O(g)
Which of the following statements concerning the above reaction are correct?
(1) x is negative in value.
(2) The standard enthalpy change of formation of water is 1/6 x kJ mol-'.
(3) The standard enthalpy change of the reaction is 4 × AH°. [NH3(g)].
А.
(1) only
(2) only
(1) and (3) only
(2) and (3) only
В.
C.
D.
13. A sample of aluminum absorbed 9.86 J of heat, and its temperature increased from 23.2°C to 30.5°C. What was
the mass of the aluminum sample? (The specific heat capacity of aluminum is 0.90 Jg'K'.)
А. 8.1 g
14. A spirit burner containing liquid methanol is used to heat up a beaker of water (200.0 g) from 15.5°C to
В. 65 g
C. 6.6 g
D. 1.5 g
100.0°C.
(Given: the specific heat capacity of water = 4.2 J g'K-', AH°. [methanol(1)] = -22.34 kJ mol-!)
Which of the following is the mass of methanol needed for the heating process?
1.59 g
A.
В.
2.23 g
С.
3.18 g
D.
6.35 g
15. Which of the following statements concerning enthalpy change cycle are correct?
(1) It can represent the enthalpy changes of the reactions.
(2) It relates the different pathways of a reaction in a closed loop.
(3) The number of atoms of species involved in any enthalpy change cycle has to be balanced.
(1) and (2) only
(1) and (3) only
С.
A.
В.
(2) and (3) only
D.
(1), (2) and (3)
AH°: [NO2(g)] =+34.0 kJ mol¬!
AH°: [NO(g)] = +90.0 kJ mol-'
16. Given that:
What is the standard enthalpy change of the following reaction:
2NO(g) + O2(g) → 2NO2(g)?
А.
-112.0 kJ mol-
В.
+112.0 kJ mol
С.
+124.0 kJ mol-
D.
+248.0 kJ mol-](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F611f98aa-01d9-425c-925e-8d741b6ba75f%2F7d350bc2-0ae1-421e-bbe9-9fb9ff178e83%2F6oq070h_processed.jpeg&w=3840&q=75)
Transcribed Image Text:10. Given the following thermochemical equation, calculate the heat involved in decomposing 12.5 g of water to
the elements. 2H2(g) + O2(g) → 2H2O(I) AH=-571.6 kJ
(Molar mass of water = 18 g)
A. +397 kJ
В. -397 kJ
C. -198 kJ
(d) +198 kJ
11. The table below shows the energy released when burning 1.0 g of each of the following organic compounds.
Compound
Energy released / kJg'
Relative molecular mass
Methane
55.7
16
Ethanol
29.8
46
Propanol
33.6
60
Octane
48.4
114
The standard enthalpy change of combustion of one of the above compounds is -2-016 kJmol-'. What is this
organic compound?
A. Methane
B. Ethanol
C. Propanol
D. Octane
12. The thermochemical equation shown below refers to the combustion of ammonia.
AH°. =x kJ
4NH3(g) + 302(g) → 2N2(g) + 6H,O(g)
Which of the following statements concerning the above reaction are correct?
(1) x is negative in value.
(2) The standard enthalpy change of formation of water is 1/6 x kJ mol-'.
(3) The standard enthalpy change of the reaction is 4 × AH°. [NH3(g)].
А.
(1) only
(2) only
(1) and (3) only
(2) and (3) only
В.
C.
D.
13. A sample of aluminum absorbed 9.86 J of heat, and its temperature increased from 23.2°C to 30.5°C. What was
the mass of the aluminum sample? (The specific heat capacity of aluminum is 0.90 Jg'K'.)
А. 8.1 g
14. A spirit burner containing liquid methanol is used to heat up a beaker of water (200.0 g) from 15.5°C to
В. 65 g
C. 6.6 g
D. 1.5 g
100.0°C.
(Given: the specific heat capacity of water = 4.2 J g'K-', AH°. [methanol(1)] = -22.34 kJ mol-!)
Which of the following is the mass of methanol needed for the heating process?
1.59 g
A.
В.
2.23 g
С.
3.18 g
D.
6.35 g
15. Which of the following statements concerning enthalpy change cycle are correct?
(1) It can represent the enthalpy changes of the reactions.
(2) It relates the different pathways of a reaction in a closed loop.
(3) The number of atoms of species involved in any enthalpy change cycle has to be balanced.
(1) and (2) only
(1) and (3) only
С.
A.
В.
(2) and (3) only
D.
(1), (2) and (3)
AH°: [NO2(g)] =+34.0 kJ mol¬!
AH°: [NO(g)] = +90.0 kJ mol-'
16. Given that:
What is the standard enthalpy change of the following reaction:
2NO(g) + O2(g) → 2NO2(g)?
А.
-112.0 kJ mol-
В.
+112.0 kJ mol
С.
+124.0 kJ mol-
D.
+248.0 kJ mol-
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