MCQs on Thermodynamics for NEET & JEE -1

0 0 Mudassar Husain Monday, 2 November 2020

MCQs on Thermodynamics for NEET & JEE Q1. What will be the value of ΔH, if the forward and reverse reactions have the same energy of act...

MCQs on Thermodynamics for NEET & JEE

Q1. What will be the value of ΔH, if the forward and reverse reactions have the same energy of activation?

(a) ΔH = ΔG = ΔS = 0
(b) ΔS = 0
(c) ΔG = 0
(d) ΔH = 0

Answer: (d)

Q2. Choose the correct answer. A thermodynamic state function is a quantity

(a) used to determine heat changes
(b) whose value is independent of path
(c) used to determine pressure volume work
(d) whose value depends on temperature only.

Solution.

(b): State function is a property of the system whose value depends only upon the state of the system and is independent of the path or the manner by which the state is reached.

Q3. For the process to occur under adiabatic conditions, the correct condition is

(a) ΔT = 0
(b) Δp = 0
(c) g = 0
(d) w=0

Solution.

(c): Adiabatic system does not exchange heat with the surroundings.

Q4. What is the molar entropy change for melting of ice at 0℃, if ΔH_f = 1.435 kcal/mol?

(a) 0.526 cal/(mol K)
(b) 5.26 cal/(mol K)
(c) 10.52 cal/(mol K)
(d) 21.04 cal/(mol K)

Answer: (b)

Q5. What is the function of a catalyst in a chemical reaction?

(a) decrease rate constant of reaction
(b) increases activation energy of reaction
(c) reduces enthalpy of reaction
(d) does not affect the equilibrium constant of reaction

Answer: (d)

Q6. What will be the work done by 3 moles of an ideal gas when it expands spontaneously in a vacuum?

(a) zero
(b) infinite
(c) 3 joules
(d) 9 joules

Answer: (a)

Q7. Find the temperature at which the below reaction will be in equilibrium if the enthalpy and entropy change for the reaction is 30 kJ mol-1 and 105 J K-1 mol-1 respectively

Br₂(l) + Cl₂(g) → 2BrCl(g)

(a) 273 K
(b) 300 K
(c) 450 K
(d) 285.7 K

Answer: (d)

Q8. Which is true for the entropy of a spontaneous reaction?

(a) ΔS(system) – ΔS(surroundings) > 0
(b) ΔS(system) + ΔS(surroundings) > 0
(c) ΔS(surroundings) > 0 only
(d) ΔS(system) > 0 only

Answer: (b)

Q9. An ideal gas is expanded isothermally at 300 K from 1 litre to 10 litres. Find the ΔE for this process (R = 2 cal mol^-1 K^-1)

(a) 9 L atm
(b) 1381.1 cal
(c) zero
(d) 163.7 cal

Answer: (c)

Q10. ΔH for the reaction N₂ + 3H₂ ⇋ 2NH₃

(a) ΔE – 2RT
(b) ΔE + 2RT
(c) ΔE – RT
(d) ΔH = RT

Answer: (a)

Q11. The enthalpies of all elements in their standard states are

(a) unity
(b) zero
(c) <0
(d) different for each element.

Solution.

(b) : By convention, the standard enthalpy of formation of every element in its standard state is zero.

Q12. ΔU° of combustion of methane is – X kJ mol^-1. The value of ΔH° is

(a) = ΔU°
(b) >ΔU°
(c) <ΔU°
(d) =0

Solution.

Δn = 1 – 3 = -2.

ΔH° = ΔU° + ΔnRT = -X- 2RT

Q13. The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are, -890.3 kJ mol^-1,-393.5 kJ mol^-1 and-285.8 kJ mol^-1 respectively. Enthalpy of formation of CH₄(g) will be

(a) -74.8 kJ mol^-1
(b) -52.27 kJ mol^-1
(c) +74.8 kJ mol^-1
(d) +52.26 kJ mol^-1

Solution.

Q14. A reaction, A + B → C + D + q is found to have a positive entropy change. The reaction will be

(a) possible at high temperature
(b) possible only at low temperature
(c) not possible at any temperature
(d) possible at any temperature

Solution.

(d): A + B → C + D + q, ΔS = +ve

Here, ΔH = -ve

ΔG = ΔH – TΔS

For reaction to be spontaneous, ΔG should be -ve. As ΔH = -ve and ΔS is +ve, ΔG will be -ve at any temperature.

Q15. In a process, 701 J of heat is absorbed by a system and 394 S of work is done by the system. What is the change in internal energy for the process?

Solution.

Heat absorbed by the system (q) = 701 J

Work done by the system (w) = -394 J

According to first law of thermodynamics,

ΔU = q + w = 701 + (-394) = 701 – 394 = 307 J

Q16. Consider the following statements

(Assertion) The internal energy of an ideal gas does not change during an Isothermal process

(Reason) The decrease in the volume of the gas is compensated by a corresponding increase in pressure when its temperature is constant in accordance with Boyle law

a. Both A & R are true and R is correct Explanation of A
b. Both A & R are true and R is not correct Explanation of A
c. A is true R is false
d. A is false but R is true

Solution: (a)

MCQs on First Law of Thermodynamics and Hess Law

Q1. The variations in enthalpy that can not be detected per calorimeter can be detected with the aid of

Newton’s law
Hess’s law
Krebs law
Ohm’s law

Answer: (b)

Q2. The energy required to sever a given covalent bond is named

bond energy
bond enthalpy
bond dissociation energy
all of above

Answer: (d)

Q3. Changes in enthalpy in an exothermic reaction is

positive
negative
constant
neutral

Answer: (b)

Q4. The first law of thermodynamics states that energy can not be

created only
destroyed only
converted
created and destroyed

Answer: (d)

Q5. Hess’s law states that a chemical reaction is independent of the route by which chemical reactions takes place while keeping the same

initial conditions only
final conditions only
mid-conditions
initial and final conditions

Answer: (d)

Q6. The standard enthalpy change of neutralization involves the reaction of an acid with an alkali to form 1 mol of

water
oxygen
nitrogen
anhydrous salt

Answer: (a)

Q7. The change in the energy between a chemical reaction and the surroundings at constant temperature is called

enthalpy change
enthalpy
enthalpy profile
dynamic enthalpy

Answer: (a)

Q8. To initiate a reaction the minimum energy which is required to break bonds is called

bond energy
activation energy
breaking energy
ionization energy

Answer: (a)

Q9. The standard condition for enthalpy changes are

the pressure of 100 kPa
temperature 298K
normal physical state
all of above

Answer: (d)

Q10. The application of law of thermodynamics to the enthalpy change was done by

Newton
Hess’s
Lewis
Sophocles

Answer: (b)

MCQs on 2nd and 3rd Law of Thermodynamics and Entropy

Q1. Which of the following processes is used to do maximum work done on the ideal gas that is compressed to half of its initial volume?

isothermal
isochoric
isobaric
adiabatic

Answer: (d)

Q2. What is the ratio of Cp/Cv for gas if the pressure of the gas is proportional to the cube of its temperature and the process is an adiabatic process?

Answer: (b)

Q3. The coefficient performance of a refrigerator is 5. Calculate the heat rejected to the surrounding if the temperature inside the freezer is -20 ^oC

11^oC
41^oC
21^oC
31^oC

Answer: (d)

Q4. What is a necessary condition for a reaction to be spontaneous at all temperatures?

𐤃H < 𐤃G
𐤃G and H should be positive
𐤃H = 𐤃G = 0
𐤃G and 𐤃H should be negative

Answer: (d)

Q5. Which of the following factor affects the heat of reaction based on Kirchhoff equation?

molecularity
temperature
pressure
volume

Answer: (b)

Q6. Chemical dissociation is

exothermic
reversible
endothermic
reversible and endothermic

Answer: (d)

Q7. Which of the following is the largest unit of energy?

electron volt
joule
calorie
erg

Answer: (c)

Q8. A perfect black body has a unique characteristic feature as

a good absorber only
a good radiator
a good absorber and a good radiator
neither a radiator nor an absorber

Answer: (c)

Q9. A thermodynamic process where no heat is exchanged with the surroundings is

isothermal
adiabatic
isobaric
isotropic

Answer: (b)

Q10. Which of the following laws was formulated by Nernst?

First law of thermodynamics
Second law of thermodynamics
Third law of thermodynamics
None of the above

Answer: (c)

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MCQs on Thermodynamics for NEET & JEE -1