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Quiz 5
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Q.1
Which of the following is closed system? [ KCET 1995]
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a) Jet engine
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b) Tea placed in steel kettle
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c) Pressure cooker
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d) Rocket engine during propulsion
Explanation
Answer: (b)
Q.2
For the reaction C + O2 → CO2 ..[ BHU 1995]
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a) ΔH > ΔE
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b) ΔH < ΔE
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c) ΔH=ΔE
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d) none of these
Explanation
Since C is solid Δn=0 Hence ΔH=ΔEAnswer: (c)
Q.3
Enthalpy of a reaction ΔH is expressed as ... [ AIIMS 1996]
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a) ΔH=∑ΔHp - ∑ΔHR
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b) ΔH=dHp + dHR
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c) ΔH=dHp / dHR
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d) ΔH=∑Hp / dHR
Explanation
Answer: (a)
Q.4
Given thatC + O2 → CO2 ; ΔH=-x kJ2CO + O2 → 2CO2; ΔH=-y kJthe enthalpy of formation of carbon monoxide will be .. [ CBSE PMT 1997]
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a) (2x - y) / 2
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b) (y - 2x) / 2
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c) 2x - y
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d) y=2x
Explanation
Aim equation C + ½O2 → COOperate eqn(1) - ½ eqn(2)ΔH=-x - ½(-y)=(y - 2x)/2Answer: (b)
Q.5
Enthalpy change (ΔH) of system depends on its ... [ Pb CET 1997]
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a) Initial state
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b) Final state
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c) Both initial and final state
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d) None of these
Explanation
Answer: (c)
Q.6
Energy required to dissociate 4 g of gaseous hydrogen into free gaseous atoms is 208 kcal at 25°C. The bond energy H-H bond will be .... [ CPMT 1989]
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a) 104 kcal
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b) 10.4 kcal
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c) 1040 kcal
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d) 104 kcal
Explanation
4g hydrogen gas=2 mole H2 Thus H-H bond energy=208 /2=104 kcal/moleAnswer: (a)
Q.7
The relation between enthalpy (H), pressure (P), volume (V) and internal energy (E) is given by .. [ MP PMT 1998]
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a) E=H + PV
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b) H=E + PV
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c) H=E - PV
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d) H=E + P + V
Explanation
Answer: (b)
Q.8
Based on the following thermo chemical equationsH2O(g) + C(s) → CO(g) + H2(g); ΔH=131 kJCO(g) + ½O2(g) → CO2(g); ΔH=-282 kJH2(g) + ½O2(g) → H2O; ΔH=-242 kJC(s) + O2(g) → CO2(g); ΔH=X kJthe value of X will be .... [ CBSE PMT 1992]
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a) -393 kJ
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b) -655 kJ
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c) +393 kJ
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d) +655 kJ
Explanation
Aim equation C(s) + O2(g) → CO2(g); ΔH=X kJ By adding first three equation we get aim equation X=131 - 282 - 242=-393 kJAnswer: (a)
Q.9
Identify the correct statement regarding entropy .. [ BHU 1998]
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a) At absolute zero of temperature, entropy of a perfectly crystalline substance is taken to be zero
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b) At absolute zero of temperature, the entropy of a perfectly crystalline substance is positive
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c) Absolute entropy of a substance cannot be determined
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d) At 0°C , the entropy of a perfectly crystalline substance is taken to be zero
Explanation
Answer: (a)
Q.10
Equal volumes of methanoic acid and sodium hydroxide are mixed. If x is the heat of formation of water, then heat evolved on neutralization is ... [ BHU 1998]
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a) more than x
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b) equal to x
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c) less than x
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d) twice x
Explanation
As methanoic acid is weak acid, heat of neutralization < x Answer: (c)
Q.11
The energy change of reaction C2H6(g) → 2C (g) + 6H(g) is X kJ The bond energy of C - H bond is ..[ Haryana CEET 1998]
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a) X/6 kJ
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b) X/3 kJ
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c) X kJ
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d) indeterminate
Explanation
C2H6 have one C-C bond. Since C-C bond energy is not known C-H bond energy can not be calculated Answer: (d)
Q.12
For the process Dry ice → CO2(g) .. [ KCET 2000]
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a) ΔH is positive and ΔS is negative
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b) Both ΔH and ΔS are negative
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c) Both ΔH and ΔS are positive
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d) ΔH is negative where as ΔS is positive
Explanation
reaction is spontaneous , absorbs heat form surrounding, state changed from solid to liquid Answer: (c)
Q.13
The enthalpy of neutralization of weak acid by a strong base is ... [ Tamil nadu CET 2001]
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a) -57.32 kJ
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b) +57.2 kJ
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c) equal to -57.32 kJ + enthalpy of ionization of weak acid
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d) more than -57.32 kJ
Explanation
Answer: (c)
Q.14
Mechanical work is specially important in systems that contain
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a) solid - liquid
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b) liquid -liquid
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c) solid - solid
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d) gases
Explanation
Answer: (d)
Q.15
If an endothermic reaction is non-spontaneous at freezing point of water and becomes feasible at its boiling point of water , then ... [ AIEEE 2002]
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a) ΔH is -ve, ΔS is +ve
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b) ΔH and ΔS both are +ve
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c) ΔH and ΔS both are -ve
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d) ΔH is +ve, ΔS is -ve
Explanation
For endothermic reaction, ΔH=+ve. As ΔG=ΔH - TΔS, ΔG is +ve at low temperature,as reaction is not spontaneous if ΔS is +ve but TΔS < ΔH At high temperature TΔS > ΔH and ΔG becomes -ve Answer: (b)
Q.16
The bond energy of O-H bond is 109 kcal/mol. When a mole of water is formed.. [ CBSE PMT 1990]
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a) 218 kcal is released
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b) 109 kcal is released
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c) 218 kcal is absorbed
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d) 109 kcal is absorbed
Explanation
Two OH bonds formed thus 2×109=218 kcal energy released Answer: (a)
Q.17
If a reaction involves only solids and liquids, which of the following is true .. [ Tamilnadu CET 2002]
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a) ΔH < ΔE
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b) ΔH=ΔE
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c) ΔH > ΔE
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d) ΔH=ΔE + RTΔn
Explanation
ΔH=ΔE+PΔV , for solid and liquid, ΔV = 0 ΔH=ΔE+ΔnRT, for solids and liquids Δn = 0. Answer: (b)
Q.18
Which of the following statements is true? ..[ KCE 2002]
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a) ΔG may be lesser or greater or equal to ΔH
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b) ΔG is always proportional o ΔH
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c) ΔG is always greater than ΔH
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d) ΔG is always less than ΔH
Explanation
Answer: (a)
Q.19
Compounds with high heat of formation are less stable because .. [ KCET 2002]
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a) It is difficult to synthesize them
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b) energy rich state leads to instability
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c) higher temperature is required to synthesize them
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d) molecules of such compounds are distorted
Explanation
Answer: (b)
Q.20
The law formulated by Nernst is ... [ kerala CET 2002
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a) first law of thermodynamics
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b) second law of thermodynamics
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c) third law of thermodynamics
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d) both a and b
Explanation
Answer: (c)
Q.21
In a closed insulated container a liquid is stirred with a paddle to increase the temperature. Which of the following is true
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a) ΔE=W ≠ 0, q=0
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b) ΔE=W=q ≠ 0
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c) ΔE=0, W=q ≠ 0
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d) W=0, ΔE=q ≠ 0
Explanation
As temperature is increased and system is insulated, i.e. q=0 Hence ΔE=q +W=WAnswer: (a)
Q.22
An adiabatic expansion of an ideal gas always has ... [ MP PMT 2002]
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a) q=0
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b) w=0
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c) ΔH=0
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d) decrease temperature
Explanation
During adiabatic expansion of an ideal gas, no heat enters or leaves the system so that q=0 Answer: (a)
Q.23
The favorable conditions for a spontaneous reaction are .. [ MP PET 2002]
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a) TΔS > ΔH, ΔH=+ve, ΔS=+ve
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b) TΔS > ΔH, ΔH=+ve, ΔS=-ve
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c) TΔS=ΔH, ΔH=-ve, ΔS=-ve
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d) TΔS=ΔH, ΔH=+ve, ΔS=+ve
Explanation
Answer: (a)
Q.24
H2(g) + Cl2(g) → 2HCl(g) ; ΔH=-44 kcal2Na(s) + 2HCl(g) → 2NaCl(s) + H2(g); ΔH=-152 kcalFor reactionNa(s) + ½Cl2(g) → NaCl(s); ΔH=?
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a) -180 kcal
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b) -196 kcal
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c) -98 kcal
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d) 54 kcal
Explanation
Aim equation can be obtained by adding eqn(1) and eqn(2) since resultant reaction have two Na so divide by 2. So energy=-98 kcal Answer: (c)
Q.25
Heat exchanged in chemical reaction at constant temperature and pressure is called .. [ AFMC 1998]
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a) entropy
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b) enthalpy
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c) internal energy
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d) free energy
Explanation
Answer: (b)
Q.26
According to second law of thermodynamics, a process ( reaction) is spontaneous, if during the process .. [ kerala MEE 2001]
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a) ΔS universe > 0
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b) ΔSuniverse=0
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c) ΔHsystem > 0
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d) ΔSuniverse < 0
Explanation
Answer: (a)
Q.27
S + (3/2)O2 → SO3 + 2x calSO2 + ½O3 + y calFind out the heat of formation of SO2
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a) ( y -2x)
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b) ( 2x - y )
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c) ( x + y)
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d) 2x/y
Explanation
Aim equation S + O2 → SO2 Operate eq(2) - eq(1) that gives y - 2xAnswer: (a)
Q.28
One mole of an ideal gas is allowed to expand freely and adiabatically into vacuum until its volume has doubled. The expression which is not true concerning statement is .. [ PB. PMT 1998]
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a) ΔH=0
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b) ΔS=0
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c) ΔE=0
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d) W=0
Explanation
Answer: (b)
Q.29
The neutralization of strong acid by a strong base liberates an amount of energy per mole of H+ ... [ BHU 1998]
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a) depends upon which acid and base are involved
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b) depends upon the temperature at which the reaction takes place
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c) depends upon which catalyst is used
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d) is always same
Explanation
Answer: (d)
Q.30
The enthalpy and entropy change for a chemical reaction are -2.5×103 cal and 7.4 cal/deg respectively. The reaction will be .. [ AFMC 1998]
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a) spontaneous
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b) reversible
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c) irreversible
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d) non - spontaneous
Explanation
ΔG=ΔH - TΔS ΔG is negative, spontaneous reactionAnswer: (a)
0 h : 0 m : 1 s
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