Chapter 7: Thermochemistry
In this article, the author has explained the most important chemistry MCQs from the seventh chapter( Thermochemistry ) of FSC chemistry. All the correct answers have been represented as bold.
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Chapter 7 thermochemistry
1: The internal energy change when a system goes from state A to B is 40 KJ/mol. If the system goes from A to B by a reversible path and returns to state a by an irreversible path What would be the net charge in internal energy
a) 40 KJ
b) < 40 KJ
c) > 40 KJ
d) Zero
2: In thermodynamics, a process is called reversible when
a) Surroundings and system change into each other
b) There is no boundary between Surroundings and system
c) The surroundings are always in equilibrium with the system
d) System and surrounding exchange heat through the boundary
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3: Which of the following cannot be measured by using Hess’s law of heat summation?
a) Heat formation of ethanol
b) Heat formation of NaHCO3
c) Enthalpy of crystallization of CaCl2
d) None of these
4: Which of the following statement is incorrect?
a) Endothermic reactions cause cooling
b) Heat is property of a system
c) There are some endothermic reactions that are spontaneous
d) Natural radioactivity is a spontaneous process
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5: One mole of H2 was present in a glass vessel placed in a room at a temperature 25oC the vessel after sometimes was exposed to bright sunlight at a temperature of 35oC what may happen?
a) Internal energy of gas increase in such a way that ∆E = qv
b) The gas would expand
c) Enthalpy of system would increase due to the expansion of gas
d) All of the above are true
6: Which of the following are not true for enthalpy?
a) Its relative value could be calculated.
b) At constant pressure the enthalpy of reaction is equal to the heat of the reaction
c) Working with change in internal energy is easier than with the change in enthalpy
d) Enthalpy of neutralization is always negative
7: Heat of formation of CO cannot be calculated directly because
a) It is a gases substance
b) it is not the sole oxidation product when c is burnt in the O2 atmosphere even in a 1:1 ratio
c) The reaction is highly exothermic
d) All of these
8: Which of the following are not correct?
a) The absolute value of enthalpy (H) can be determined experimentally
b) Dissolution of NH4Cl in excess of water, is an endothermic process
c) Neutralization process is always exothermic
d) The heat of reaction at constant volume is denoted by ∆E
9: All of the following could be calculated from Hesses’s law except;
a) Heat of formation of Glucose
b) Heat of formation of ethanol
c) The heat of reaction for the conversion of graphite to diamond
d) None of these
10: Which of the following correctly represents the enthalpy change of a chemical reaction?
a) Total enthalpy of reactants – Total enthalpy of products
b) Total enthalpy of products – Total enthalpy of reactants
c) Total enthalpy of reactants + Total enthalpy of products
d) Total enthalpy of products
11: For which, one of the following equations correctly does the enthalpy change represents the lattice energy of sodium chloride
a) Na + ½ Cl2 –> NaCl
b) Na + Cl –> NaCl
c) Na+(aq) + Cl–(aq) –> NaCl(aq)
d) Na+(g) + Cl–(g) –> NaCl(s)
12: Which of the following equation correctly defines the enthalpy changes of the formation of Carbon monoxide?
a) C(s) + ½ O2 (g) –> CO(g)
b) C(g) + ½ O2 (g) –> CO(g)
c) C + O –> CO
d) C + CO2 –> 2CO
13: Why does the following exothermic reaction not occur spontaneously?
C (diamond) –> C (graphite) ∆H = -3KJ/mol
a) A tetrahedral configuration is always more stable than a planar one
b) Diamond has only covalent bonds while graphite has both covalent bonds and Vander Waal’s forces
c) Graphite has delocalized electrons
d) The change from diamond to graphite has a high activation energy
14: Which of the following represents the standard enthalpy of combustion?
a) Hocomb
b) ∆Hocomb
c) ) ∆Hoc
d) All of these
15: During an exothermic change
a) Temperature of surroundings remains constant
b) Temperature of surroundings increases
c) Temperature of surroundings decreases
d) None of these
16: Which of the following is involved in determining the enthalpy change of a chemical reaction?
a) The initial and final temperature of the reacting system
b) The number of stages involved in the reaction
c) Activation energy of the reaction
d) The initial and final physical state of the reacting system
17: Which of the following has the same value as the standard enthalpy change of carbon monoxide?
a) ½ ∆Hof (CO2)
b) ∆Hof (CO2) – ∆Hoc (graphite)
c) ½ ∆Hoc ( graphite)
d) ∆Hoc ( graphite) – ∆Hoc (CO2)
18: For which of the following ions is the enthalpy change of hydration likely to be the most exothermic
Ion Ionic radius(nm) Charge on ion
a) 0.065 +2
b) 0.095 +1
c) 0.135 +2
d) 0.181 -1
19: The value of the enthalpy change for the process represented by the equation is equal to
Na –> Na+ + e_
a) The first ionization energy of sodium
b) The enthalpy of vaporization of sodium’
c) The sum of the first ionization energy and the electron affinity of the sodium
d) The sum of the enthalpy change of atomization and the first ionization energy of sodium
20: At constant volume, the change in internal energy is equal to
a) Product of heat and work
b) Work only
c) Heat only
d) None of these
21: Which of the following is not correct for the enthalpy of a system?
a) It is a state function
b) Its absolute value can’t be measured
c) It is measured in joules
d) When ∆V = 0 then ∆H = q + w
22: Give the following enthalpy changes:
I2(g) + 2Cl2(g)–> 2ICl3(s) ∆ H0 = -214 kj/mol
I2(s) –> I2(g) ∆ Ho = +38kj/mol
What is the standard enthalpy change of formation of ICl3?
a) +176 kj/mol
b) +138 kj/mol
c) -88 kj/mol
d) -138 KJ/mol
23: Which of the following processes is not exothermic?
a) Condensation of steam
b) Freezing of water
c) Electrolysis of water
d) Reaction between H+(aq) and OH– (aq)
24: From which of the following reactions can the bond energy of the C-F bond be determined by using only the standard enthalpy change of the reaction?
a) CF4(g) –> C(g) + 4F(g)
b) CF4(g) –> CF2(g) + F2(g)
c) CF4(s) –> CF4(g)
d) 2F2(g) + C(s) –> CF4(g)
25: Magnesium oxide and sodium fluoride are isoelectronic. Which of the following are reasons why the value of the lattice energy of magnesium oxide is 4 to 5 times that of sodium fluoride?
a) The higher enthalpy change of hydration of the doubly charged cations
b) the higher charge density of the doubly charged ions
c) The larger intermolecular distances between the doubly charged ions
d) None of these
26: Which one of the following is always an endothermic process?
a) The hydration of a gaseous cation
b) The deposition of vapors of a metal
c) The dissociation into atoms of a diatomic molecule
d) reaction of an acid with a base
27: The following equations each represent a step in the Born-Haber cycle for the enthalpy change of formation of sodium chloride. Which changes have –ve ∆ H value>
a) Cl(g) + e– –> Cl-(g)
b) Na(s) –> Na(g)
c) ½ Cl2(g) –> Cl(g)
d) Na(g) –> Na+(g)
28: Enthalpy change of a reaction does not depend on
a) Conditions of a reaction
b) Physical state of reactants and products
c) Initial and final concentration
d) Number of steps in the reaction
29: During an isothermal expansion of an ideal gas its
a) Enthalpy decreases
b) Internal energy decreases
c) Enthalpy remains constant
d) Internal energy increases
30: Given the reaction
CO2(g) + H2O(g) à CO(g) + H2(g) ∆ H=2.8 kj
Hence ∆ H represents heat of
a) Solution
b) Formation
c) Reaction
d) Combustion
31: When the volume of a system remains constant and the heat is absorbed by the system, then the amount of heat absorbed is called:
a) Enthalpy change of the system
b) Total enthalpy of the system
c) Internal energy change of the system
d) Total internal energy of the system
32: One of the statements about the Born-Haber cycle is correct.
a) Born-Haber cycle is different from Hess’s law
b) The energy change in a cyclic process is not zero
c) The lattice energy of the crystalline substances can be calculated easily
d) Heat of formation of the product and the lattice energy of the substance can be calculated simultaneously
33: What happens to the enthalpy change when the coefficients of a chemical equation are doubled?
a) It doubles
b) It does not change
c) It becomes half
d) Can’t be predicted
34: The values of ∆H and ∆E are approximately the same for those processes in which liquids and solids are involved. The reason is that:
a) Heat is absorbed in the process
b) Volume remains constant
c) Heat is released in the process
d) Temperature remains constant
35: Which one of the following is an open system;
a) When some quantity of hot water is enclosed in a closed vessel
b) When some quantity of water present in equilibrium with its vapor in a closed and insulated beaker
c) When hot water is in an open beaker
d) When water is boiling in a pressure cooker
36: The enthalpies of all elements in their standard states are
a) Unity
b) Zero
C) Always negative
d) always positive
37: Suppose you have a balloon of a given volume, V1 containing gas at temperature T1. When you place the balloon in a colder room at temperature T2, the balloon’s temperature starts to drop. What are the signs of the system’s q, w, and E for this process?
a) +q, +w, +E
b) +q, -W, -E
c) –q, -w, +E
d) –q, +w, -E
38: All of the following processes are spontaneous except
a) Synthesis of glucose by plants
b) Neutralization of HCl by NaOH
c) Combustion of natural gas
d) Reaction of H2 with O2 to form H2O
39: Sublimation, vaporization, melting, and photosynthesis all are examples of the —— process.
a) Chemical
b) Biochemical
c) Endothermic
d) Physical
40: The first law of thermodynamics states that:
a) All product-favored processes happen quickly
b) The total entropy in the universe is always increasing
c) The entropy of pure crystalline substances at 0 k=0.
d) The total energy in the universe is a constant
41: All chemical reactions involve
a) Catalysis
b) Changes of physical state
c) Energy changes
d) Formation of radioactive substances
42: Which of the following processes is an exothermic process?
a) The boiling of liquid nitrogen
b) The sublimation of dry ice
c) The freezing of water
d) The vaporization of water
43: When 10 grams of methane is completely burnt in oxygen, the heat evolved in 560 kj. What is the heat of combustion ( in KJ/mol) of methane>
a) -1120
b) -896
c) -968
d) -560
44: For which of the following changes ∆H ≠ ∆E?
a) H2 + I2 –> 2HI
b) N2(g) + O2(g) –> 2NO(g)
c) HCl + NaOH –> NaCL + H2O
d) N2 + 3H2 –> 2NH3
45: Which one is not the state function?
a) Internal energy
b) Gibbs free energy
c) Enthalpy
d) Work
46: Which of the followings does not represent a spontaneous process>
a) Evaporation of water
b) Dissolution of salt in water
c) Formation of ice
d) Combustion of methane
47: Which of the following is not a state function?
a) volume
b) Enthalpy
c) internal energy
d) None of these
48: For which of the following processes will the entropy increase?
a) Reaction of magnesium with oxygen to form magnesium oxide
b) Reaction of nitrogen and hydrogen to form ammonia
c) Sublimation of dry ice
d) Condensation of steam
49: For a reaction to occur spontaneously
a) (∆H – T ∆S) must be negative
b) ∆H must be negative
c) (∆H + T∆S) must be negative
d) ∆S must be negative
50: A spontaneous change means
a) A lowering of free energy
b) An increase in internal energy
c) No energy change
d) Lowering of energy
51: The internal energy of a system can be increased by
i) Transferring heat from the surroundings to the system
ii) Transferring heat from the system to the surroundings
iii) Doing work on the system
a) I only
b) II only
c) III only
d) I and II
52: In which of the following processes does the enthalpy change (∆H) directly represent the magnitude of the lattice energy of KCl(s)?
a) Cl2(g) + 2K(s)–> 2KCl(s)
b) KCl(s) –> K+(g) +Cl-(g)
c) KCl(s) –> K+(aq) + Cl-(aq)
d) KCl(s) –> K(s) + Cl-(g)
53: The temperature remains constant as energy is added to a substance. How may the substance be changing?
a) From gas to a solid
b) Fromm a liquid to a solid
c) From a liquid to a gas
d) In the amount of kinetic energy
54: For writing a thermochemical equation for enthalpy of combustion of an element requires
I) 1 mole of the element as a reactant
ii) 12 mole of oxide of element as product
iii) Standard states of all the substances
iv) Balanced equation of 1 mole of an element
a) i
b) I, ii, iv
c) I, ii
d) I, ii, iii, iv
55: When water is added to quicklime, the reaction is
a) Exothermic
b) Endothermic
c) Explosive
d) Photochemical
56: Thermodynamics relates heat with other forms of energy. It does not deal with
a) Gibb’s free energy
b) Activation energy
c) Internal energy
d) Potential energy
57: The heat of neutralization of an acid A with a base B is 13.7 kcal. Which of the following is true
a) A is weak and B is also weak
b) A is strong and B is weak
c) A is weak and B is strong
d) A is strong and B is also strong
58: The heats of formation of CO(g) and CO2(g) are 26.4 kcal and -94.0 kcal respectively. The heat of combustion of carbon monoxide according to Hess’s law will be
a) +26.4 kcal
b) +94.0 kcal
c) -67.6 kcal
d) -120.4 kcal
59: At constant volume, the change in internal energy is equal to
a) product of heat & work
b) Heat only
c) Work only
d) None of these
60: For which, one of the following equations does the enthalpy change represents the lattice energy of sodium chloride?
a) Na(s) + ½ Cl2(g) –> NaCl(S)
b) Na+(aq) + Cl-(aq) –> NaCl(aq)
c) Na(g) + CL(g) –> NaCl(s)
d) Na+(g) + Cl-(g) –> NaCl(s)