NEET Chemistry Chemical Thermodynamics Revision Notes

Question. The freezing point on a thermometer is marked as 20° and the boiling point at as 150°. A temperature of 60°C on this thermometer will be read as:
a. 40°
b. 65°
c. 98°
d. 110°
Answer : C

Question. The coefficient of apparent expansion of a liquid in a copper vessel is C and in a silver vessel S. The coefficient of volume expansion of copper is γ_c . What is the coefficient of linear expansion of silver?
a. (C + γ_c + S) / 3
b. (C − γ_c + S) / 3
c. (C + γ_c −S) / 3
d. (C − γ_c −S) / 3
Answer : C

Question. A monoatomic ideal gas, initially at temperature T₁, is enclosed in a cylinder fitted with a frictionless piston. The gas is allowed to expand adiabatically to a temperature T₂ by releasing the piston suddenly. If L₁ and L₂ are the lengths of the gas column before and after expansion
respectively, then T₁/ T₂ is given by:
a. (L₁/L₂)^2/3
b. L₁/L₂
c. L₂/L₁
d. (L₂/L₁)
Answer : D

Question. A thermally insulated container is divided into two parts by a screen. In one part the pressure and temperature are P and T for an ideal gas filled. In the second part it is vacuum. If now a small hole is created in the screen, then the temperature of the gas will:
a. Decrease
b. Increase
c. Remain same
d. None of these
Answer : C

Question. A gas expands 0.25m³ at constant pressure 10³ N/m² , the work done is:
a. 2.5 ergs
b. 250 J
c. 250 W
d. 250 N
Answer : B

Question. At 100°C the volume of 1kg of water is 10^–3 m³ and volume of 1 kg of steam at normal pressure is 1.671 m³. The latent heat of steam is 2.3×10⁶ J / kg and the normal pressure is 105 N/m². If 5kg of water at 100°C is converted into steam, the increase in the internal energy of water in this process will be:
a. 8.35×10⁵J
b. 10.66×10⁶J
c. 11.5×10⁶J
d. Zero
Answer : B

Question. In pressure-volume diagram given below, the isochoric, isothermal, and isobaric parts respectively, are

a. BA, AD, DC
b. DC, CB, BA
c. AB, BC, CD
d. CD, DA, AB
Answer : D

Question. A gas is compressed at a constant pressure of 50N/m² from a volume of 10m³ to a volume of 4m³. Energy of 100 J is then added to the gas by heating. Its internal energy is:
a. Increased by 400 J
b. Increased by 200 J
c. Increased by 100 J
d. Decreased by 200 J
Answer : A

Question. 5 Moles of an ideal gas undergoes an isothermal process at 500K in which its volume is doubled. The work done by the gas system is:
a. 3500 J
b. 14400 J
c. 17800 J
d. 5200 J
Answer : B

Question. During an adiabatic process, the pressure of a gas is found to be proportional to the cube of its absolute temperature.
The ratio C_p/C_v for the gas is:
a. 2/3
b. 3/4
c. 2
d. 3/5
Answer : A

Question. A thermodynamic system is taken through the cycle PQRSP process. The net work done by the system is:
a. 20 J
b. – 20 J
c. 400 J
d. – 374 J
Answer : B

Question. The relation between the internal energy U and adiabatic constant γ is:
a. U = PV/γ − 1
b. U = PV^γ/γ - 1
c. U = PV/γ
d. U = γ/PV
Answer : A

Question. 110 J of heat is added to a gaseous system, whose internal energy change is 40 J, and then the amount of external work done is:
a. 150 J
b. 70 J
c. 110 J
d. 40 J
Answer : B

Question. A thermometer is graduated in mm. It registers –3 mm when the bulb of thermometer is in pure melting ice and 22 mm when the thermometer is in steam at a pressure of one atm. The temperature in °C when the thermometer registers 13mm is:
a. 13/25x100
b. 16/25x100
c. 13/22x100
d. 16/22x100
Answer : B

Question. A iron rod of length 50 cm is joined at an end to an aluminium rod of length 100 cm. All measurements refer to 20°C. The coefficients of linear expansion of iron and aluminium are 12 x 10⁻⁶ / °C × − ° and 24 x 10⁻⁶ / °C respectively.
The average coefficient of composite system is:
a. 36 x 10⁻⁶ / °C 
b. 12 x 10⁻⁶ / °C 
c. 20 x 10⁻⁶ / °C 
d. 48 x 10⁻⁶ / °C 
Answer : C

Question. The first law of thermodynamics is only:
a. The law of conservation of energy
b. The law of conservation of mass
c. The law of conservation of momentum
d. Both a. and b.
Answer : D

Question. The work done in ergs for the reversible expansion of one mole of an ideal gas from a volume of 10 litres to 20 litres at 25°C is:
a. 2.303 × 298 × 0.082log 2
b. 298 × 10⁷ × 8 .31 × 2.303log 2
c. 2.303 × 298 × 0.082log 0.5
d. 8.31 × 10⁷ × 298 − 2.303log 0.5
Answer : B

Question. At 27°C, one mole of an ideal gas is compressed isothermally and reversibly from a pressure of 2 atm to 10 atm. The values of ΔE and q are: (R = 2)
a. 0, – 965.84 cal
b. – 965.84 cal, + 965.84 cal
c. + 865.58 cal, – 865.58 cal
d. – 865.58 cal, – 865.58 cal
Answer : A

Question. Work done during isothermal expansion of one mole of an ideal gas from 10 atom to 1 atm at 300K is:
a. 4938.8 J
b. 4138.8 J
c. 5744.1 J
d. 6257.2 J
Answer : C

Question. A mixture of two moles of carbon monoxide and one mole of oxygen, in a closed vessel is ignited to convert the carbon monoxide to carbon dioxide. If ΔH is the enthalpy change and ΔE is the change in internal energy, then:
a. ΔH > ΔE
b. ΔH < ΔE
c. ΔE = ΔE
d. The relationship depends on the capacity of the vessel
Answer : B

Question. The enthalpies of the elements in their standard states are assumed to be:
a. Zero at 298 K
b. Unit at 298 K
c. Zero at all temperatures
d. Zero at 273 K
Answer : A

Question. An ideal gas at constant temperature and pressure expands, then its:
a. Internal energy remains same
b. Internal energy decreases
c. Internal energy increases
d. Entropy first increases and then decreases
Answer : A

Question. Work done during isothermal expansion of one mole of an ideal gas from 10 atm to 1 atm at 300 K is: (Gas constant = 2)
a. 938.8 cal.
b. 1138.8 cal.
c. 1381.8 cal.
d. 1581.8 cal.
Answer : C

Question. For the reaction of one mole of zinc dust with one mole of sulphuric acid in a bomb calorimeter, ΔU and w correspond to:
a. ΔU < 0, w = 0
b. ΔU = 0, w < 0
c. ΔU > 0, w = 0
d. ΔU < 0, w > 0
Answer : A

Question. 2C+O₂ → 2CO; ΔH = −220kJ Which of the following statement is correct for this reaction?
a. Heat of combustion of carbon is 110 kJ
b. Reaction is exothermic
c. Reaction needs no initiation
d. All of these are correct
Answer : B

Question. Internal energy is:
a. Partly potential and partly kinetic
b. Totally kinetic
c. Totally potential
d. None of these
Answer : A

Question. During an isothermal expansion of an ideal gas its:
a. Internal energy increases
b. Enthalpy decreases
c. Enthalpy remains unaffected
d. Enthalpy reduces to zero
Answer : C

Question. For the reaction N₂ + 3H₂ ⇌ 2NH₃ ; ΔH =
a. ΔE − RT
b. ΔE − 2RT
c. ΔE + RT
d. ΔE + 2RT
Answer : B

Question. If gas, at constant temperature and pressure expands then its:
a. Entropy increases and then decreases
b. Internal energy increases
c. Internal energy remains the same
d. Internal energy decreases
Answer : C

Question. One mole of an ideal gas is allowed to expand reversibly and adibatically from a temperature of 27°C. If the work done during the process is 3 kJ, then final temperature of  the gas is: (C_V = 20 J /K)
a. 100 K
b. 150 K
c. 195 K
d. 255 K
Answer : B

Question. When enthalpy and entropy change for a chemical reaction are −2.5×10³ cal and 7.4 cal deg^–1 respectively. Predict the reaction at 298 K is:
a. Spontaneous
b. Reversible
c. Irreversible
d. Non-spontaneous
Answer : A

Question. For chemical reactions, the calculation of change in entropy is normally done
a. At constant pressure
b. At constant temperature
c. At constant temperature and pressure both
d. At constant volume
Answer : C

Question. The enthalpy change for the transition of liquid water to steam, ΔH_vap = 37.3kJmol⁻¹ at 373K. The entropy change for the process is:
a. 111.9J mol⁻¹ K⁻¹
b. 37.3J mol⁻¹ K⁻¹
c. 100J mol⁻¹ K⁻¹
d. 74.6J mol⁻¹ K⁻¹
Answer : C

Question. Two spheres made of same substance have diameters in the ratio 1: 2. Their thermal capacities are in the ratio of:
a. 1 : 2
b. 1 : 8
c. 1 : 4
d. 2 : 1
Answer : B

Question. When 300 J of heat is added to 25 gm of sample of a material its temperature raises from 25°C to 45°C. The thermal capacity of the sample and specific heat of the material are respectively given by?
a. 15 J/°C, 600 J/kg °C
b. 600 J/°C, 15 J°/kg oC
c. 150 J/°C, 60 J/kg °C
d. None of these
Answer : A

Question. Latent heat of ice is 80 calorie/gm. A man melts 60 g of ice by chewing in 1 minute. His power is:
a. 4800 W
b. 336 W
c. 1.33 W
d. 0.75 W
Answer : B

Question. Standard molar enthalpy of formation of CO₂ is equal to:
a. Zero
b. The standard molar enthalpy of combustion of gaseous carbon
c. The sum of standard molar enthalpies of formation of CO and O₂
d. The standard molar enthalpy of combustion of carbon (graphite)
Answer : D

Question. An ideal gas is taken through the cycle A → B → C → A, as shown in the figure. If the net heat supplied to the gas in the cycle is 5J, the work done by the gas in the process C → A is:

a. – 5 J
b. – 20 J
c. – 15 J
d. – 10 J
Answer : A

Question. When 50 cm³ of a strong acid is added to cm³ of an alkali, the temperature rises by 5°C. If 250 cm3 of each liquid are mixed, the temperature rise would be?
a. 5°C
b. 10°C
c. 25°C
d. 20°C
Answer : A

Question. The bond dissociation energies of gaseous H₂ ,Cl₂ and HCl are 104, 58 and 103 kcal respectively. The enthalpy of formation of HCl gas would be:
a. – 44 kcal
b. 44 kcal
c. – 22 kcal
d. 22 kcal
Answer : C

Question. Evaporation of water is:
a. An endothermic change
b. An exothermic change
c. A process where no heat change occurs
d. A process accompanied by chemical reaction
Answer : A

Question. If ΔHof for H₂O₂ and H₂O are –188kJ/mole and –286kJ/mole.
What will be the enthalpy change of the reaction?
2H₂O₂ (l) → 2H₂O(l) + O₂(g)
a. −196kJ /mole
b. 146kJ /mole
c. −494kJ /mole
d. −98kJ /mole
Answer : A

Question. Heat of combustion ΔH of CH₄ ,C₂H₆ ,C₂H₄ and C₂H₂ gases are –212.8, –373.0, –337.0 and –310.5 kcal respectively at the same temperature. The best fuel among these gases is
a. CH₄
b. C₂H₆
c. C₂H₄
d. C₂H₃
Answer : A

Question. Which of the following values of heat of formation indicates that the product is least stable?
a. −94kcal
b. −231.6kcal
c. +21.4kcal
d. +64.8kcal
Answer : D

Question. The H–H bond energy is 430 kJ mol and Cl–Cl bond energy is 240 kJ mol⁻¹. ΔH for HCl is –90 kJ. The H–Cl bond energy is about:
a. 180kJ mol⁻¹
b. 360kJ mol⁻¹
c. 213kJ mol⁻¹
d. 425kJ mol⁻¹
Answer : D

Question. If the bond energies of H–H, BR–Br and HBr are 433, 192 and 364 kJ mol–1 respectively, the ΔH° for the reaction, H₂ (g) + Br₂ (g) → 2HBr(g) is:
a. + 261 kJ
b. – 103 kJ
c. – 261 kJ
d. + 103 kJ
Answer : B

Question. The work done during the expansion of a gas from a volume of 4 dm³ to 6 dm³ against a constant external pressure of 3atm is: (1Latm=101.32J )
a. + 304 J
b. –304 J
c. – 6 J
d. –608 J
Answer : D

Question. The entropy changed involved in the conversion of 1 mole of liquid water at 373 K to vapour at the same temperature will be: CO₂ (g),H₂O(l)
a. 0.119 kJ
b. 0.109 kJ
c. 0.129 kJ
d. 0.120 kJ
Answer : B

Question. Energy required to dissociate 4 gm of gaseous hydrogen into free gaseous atoms is 208 kcal at 25°C. The bond energy of H–H bond will be:
a. 104 kcal
b. 10.4 kcal
c. 1040 kcal
d. 104 cal
Answer : A

Question. Which is an irreversible process?
a. Mixing of two gases
b. Evaporation of water at 373 K and 1 atm in a closed system
c. Dissolution of NaCl in water
d. H₂O (s) at –4ºC
Answer : A, C, D

Question. A gas undergoes change in its state form position A to position B, via three different paths as shown in the figure.
Select the correct alternatives:

a. Change in internal energy in all the three paths is equal
b. In all the three paths heat is absorbed by the gas
c. Heat absorbed/released by the gas is maximum in path (1)
d. Temperature of the gas first increases and then decreases continuously in path (1)
Answer : A, B, C

Question. An ideal gas undergoes a thermodynamic cycle as shown in the figure. Which of the following statements are correct?

a. Straight line AB cannot pass through O
b. During process AB, temperature decreases while during process BC it increases
c. During process BC, work is done by the gas against external process and temperature of the gas increases 
d. During process CA, work is done by the gas against external pressure and heat supplied to the gas is exactly equal to this work.
Answer : B, D

Question. Which of the following are thermodynamically stable?
a. C (diamond)
b. C (graphite)
c. P₄ (white)
d. P₄ (black)
Answer : B, C

Question. C(s) + 1/ 2O₂  → CO(g); ΔH° = -26 Kcal mol⁻¹
CO(g) 1/ 2O₂ → CO₂ (g); ΔH° = -68 Kcal mol⁻¹
a. Heat of formation of CO₂ is -68 Kcal mol⁻¹
b. Heat of formation of C(s) is -26 Kcal mol⁻¹
c. Heat of formation of CO₂ (g) is -94 Kcal mol⁻¹
d. Heat of formation of CO (g) is -26 Kcal mol⁻¹
Answer : C, D

Question. Heat of neutralization of weak acid with strong base is −50 KJ and weak acid, weak base is −41.4 KJ then:
a. Heat of ionization of weak acid is 7.4 KJ/mole
b. Heat of strong acid and strong base neutralization is −57.4 KJ
c. Heat of ionization of weak base is 16 KJ/mole
d. Heat of ionization of weak base is 8.6 KJ/mole
Answer : A, B, D

Question. An ideal gas is taken from the state A (pressure p, volume V to the state B (pressure p/2, volume 2V) along a straight line path in the p-V diagram. Select the correct statements from the following:
a. The work done by the gas in the process A to B exceeds the work that would be done by it if the system were taken from A to B along an isotherm
b. In the T-V diagram, the path AB becomes a part of a parabola
c. In the p-T diagram, the path AB becomes a part of a hyperbola
d. In going from A to B, the temperature T of the gas first increases to a maximum value and then decrease
Answer : A, B, D

Question. The figure shows the p-V plot an ideal gas taken through a cycle ABCDA. The part ABC is a semi-circle and CDA is half of an ellipse. Then,
a. the process during the path A→B is isothermal
b. heat flows out of the gas during the path B→C→D
c. work done during the path A→B→Cis zero
d. positive work is done by the gas in the cycle ABCDA
Answer : B, D

Assertion and Reason

Note: Read the Assertion (A) and Reason (R) carefully to mark the correct option out of the options given below:
a. If both assertion and reason are true and the reason is the correct explanation of the assertion.
b. If both assertion and reason are true but reason is not the correct explanation of the assertion.
c. If assertion is true but reason is false.
d. If the assertion and reason both are false.
e. If assertion is false but reason is true.

Question. Assertion: Entropy of ice is less than water.
Reason: Ice have cage like structure.
Answer : B

Question. Assertion: The heat absored during the isothermal expansion of an ideal gas against vacuum is zero.
Reason: The volume occupied by the molecules of an ideal gas is zero.
Answer : C

Question. Assertion: Molar entropy of vaporization of water is different from ethanol.
Reason: Water is more polar than ethanol.
Answer : B

Question. Assertion: The enthalpies of neutralisation of strong acids and strong bases are always same.
Reason: Neutralisation is heat of formation of water.
Answer : A

Question. Assertion: If a refrigerator’s door is kept open room gets cooled.
Reason: Material kept inside the refrigerator reamins cool.
Answer : E

Question. Assertion: Absolute values of internal energy of substance cannot be determined.
Reason: It is impossible to determine exact values of constituent energies of the substances.
Answer : A

Question. Assertion: Mass and volume are extensive properties.
Reason: Mass / volume is also an extensive parameter.
Answer : B

Question. Assertion: The increase in internal energy (ΔE) for the vaporiation of one mole of water at 1 atm and 373K is zero.
Reason: For all isothermal processes ΔE = 0.
Answer : A

Question. Assertion: ΔH and ΔE are almost the same for the reaction.  N₂(g) + O₂ (g) ⇌ 2NO(g).
Reason: All reactants and products are gases.
Answer : B

Question. Assertion: Enthalpy and entropy of any elementary substance in the standard state are taken as zero.
Reason: At zero degree absolute, the constituent particles become completely motionless.

Comprehension Based

Paragraph –I

A diatomic gas is enclosed in a cylinder at pressure  10⁵N/m² at temperature 27°C. It is subjected to a cyclic process. In the first process its pressure is doubled keeping volume constant. Then it is made to expand adiabatically to original pressure. Then it is made of suffer isobaric compression bringing it back to initial volume 2 litre.

Question. Temperature of gas after its pressure is doubled at constant volume is:
a. 327°C
b. 127°C
c. 177°C
d. 148°C
Answer : A

Question. After adiabatic expansion the new volume will be:
a. 4.12 litre
b. 3.27 litre
c. 2.58 litre
d. 1.88 litre
Answer : B

Question. Which of the following is correct statement?
a. Entropy increases in first process, during second process entropy remains constant and during last process, it decreases
b. Entropy remains constant in first step, increases in second step and decreases in 3rd step
c. Entropy decreases in first step, increases in 2nd step and remains constant in 3rd step
d. Entropy goes on increasing in all steps
Answer : A