Thermodynamics and equilibrium together give some of the most dependable scoring questions in JEE physical chemistry. This set covers enthalpy, entropy and Gibbs energy, Hess's law, the link between ΔG° and K, Le Chatelier's principle, pH of acids and bases, buffers and solubility product. Use R = 8.314 J K⁻¹ mol⁻¹ where needed.
How to practise: read each question and tap the option you think is correct. You will see right away whether you got it, along with a short explanation, and your score is tracked at the bottom of the screen. This set has 15 questions.
Topics covered in this set
- First law, work and ΔH vs ΔU
- Hess's law and enthalpy of formation
- Entropy, Gibbs energy and spontaneity
- Kp, Kc and ΔG° = −2.303RT log K
- pH, weak acids and buffers
- Solubility product and common ion effect
JEE Chemistry MCQs with answers and explanations
Q1. Which of the following is an intensive property?
a) Internal energy
b) Enthalpy
c) Temperature
d) Volume
Q2. One mole of an ideal gas expands isothermally and reversibly at 300 K from 1 L to 10 L. What is the work done on the gas?
a) +5.74 kJ
b) −5.74 kJ
c) −2.49 kJ
d) Zero
Q3. For the reaction CO(g) + ½O₂(g) → CO₂(g) at constant temperature, which relation between ΔH and ΔU is correct?
a) ΔH = ΔU − RT
b) ΔH = ΔU
c) ΔH = ΔU − ½RT
d) ΔH = ΔU + ½RT
Q4. Given C(s) + O₂(g) → CO₂(g), ΔH = −393.5 kJ and CO(g) + ½O₂(g) → CO₂(g), ΔH = −283.0 kJ, what is ΔH for C(s) + ½O₂(g) → CO(g)?
a) −676.5 kJ
b) −110.5 kJ
c) +110.5 kJ
d) −283.0 kJ
Q5. The enthalpy of vaporisation of water at its boiling point (373 K) is 40.7 kJ mol⁻¹. What is the entropy of vaporisation?
a) 373 J K⁻¹ mol⁻¹
b) 40.7 J K⁻¹ mol⁻¹
c) 109 J K⁻¹ mol⁻¹
d) 0.109 J K⁻¹ mol⁻¹
Q6. A reaction has ΔH = −100 kJ mol⁻¹ and ΔS = −200 J K⁻¹ mol⁻¹. Above what temperature does it become non-spontaneous?
a) 2 K
b) 500 K
c) 200 K
d) 50 K
Q7. A reaction with ΔH > 0 and ΔS > 0 is:
a) Spontaneous at all temperatures
b) Spontaneous only at high temperature
c) Non-spontaneous at all temperatures
d) Spontaneous only at low temperature
Q8. The equilibrium constant of a reaction at 298 K is 10. What is ΔG°?
a) +5.7 kJ mol⁻¹
b) −5.7 kJ mol⁻¹
c) Zero
d) −57 kJ mol⁻¹
Q9. For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), the relation between Kp and Kc is:
a) Kp = Kc
b) Kp = Kc(RT)⁻⁴
c) Kp = Kc(RT)⁻²
d) Kp = Kc(RT)²
Q10. The equilibrium constant for A ⇌ B is 4. What is the equilibrium constant for 2B ⇌ 2A at the same temperature?
a) 1/4
b) −8
c) 1/16
d) 16
Q11. For the exothermic reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which change increases the equilibrium yield of NH₃?
a) Increasing temperature
b) Decreasing pressure
c) Adding a catalyst
d) Increasing pressure
Q12. What is the pH of 0.01 M NaOH at 25 °C?
a) 10
b) 2
c) 14
d) 12
Q13. What is the approximate pH of 0.1 M acetic acid (Ka = 1.8 × 10⁻⁵)?
a) 1.0
b) 2.87
c) 5.74
d) 4.74
Q14. A buffer contains 0.1 M sodium acetate and 0.01 M acetic acid (pKa = 4.74). What is its pH?
a) 5.74
b) 3.74
c) 4.74
d) 6.74
Q15. The molar solubility of CaF₂ in water is 2 × 10⁻⁴ mol L⁻¹. What is its Ksp?
a) 3.2 × 10⁻¹¹
b) 8 × 10⁻¹²
c) 1.6 × 10⁻¹⁰
d) 4 × 10⁻⁸
Quick revision notes
- ΔH = ΔU + Δn₍g₎RT; isothermal reversible W = −2.303nRT log(V₂/V₁).
- ΔG = ΔH − TΔS; crossover temperature T = ΔH/ΔS.
- ΔG° = −2.303RT log K; Kp = Kc(RT)^Δn.
- Weak acid: [H⁺] = √(KaC); buffer: pH = pKa + log(salt/acid).
- Ksp: AB = s², AB₂ = 4s³; a common ion lowers solubility.
Frequently asked questions
Are these JEE previous year questions?
No, they are original practice questions written to the JEE Main syllabus and level.
Does a catalyst change the equilibrium constant?
No. A catalyst speeds up the forward and backward reactions equally, so equilibrium is reached faster but K and the composition stay the same.
When can I use [H⁺] = √(KaC)?
When the acid is weak and its degree of dissociation is small (below about 5%), so C − x can be taken as C.
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