Exams › JEE Main › Chemistry

A closed adiabatic container fitted with a frictionless movable piston contains 1 mol of gaseous X at 300 K. The external pressure is kept fixed at 1 atm. A reaction is initiated using a negligible amount of electrical energy: 3X(g) → 2Y(g), with ΔH = −30 kJ mol⁻¹. The process proceeds at constant pressure until completion. If 75% of X has reacted at 1 atm, what is the final temperature of the vessel? Given: Cₚ,m(X) = 40 J K⁻¹ mol⁻¹ and Cₚ,m(Y) = 30 J K⁻¹ mol⁻¹.

1. 600 K
2. 300 K
3. 1200 K
4. 1000 K

Correct answer: 600 K

Solution

The reaction releases heat (exothermic) and produces fewer moles of gas, which increases the temperature of the system. Given the heat released and the specific heat capacities, the final temperature can be calculated, resulting in 600 K after accounting for the heat transfer and the change in moles.

Related JEE Main Chemistry questions

• Using the following thermochemical equations, determine the enthalpy of vaporisation of water: H₂(g) + 1/2 O₂(g) → H₂O(l), ΔH = -286 kJ H₂(g) + 1/2 O₂(g) → H₂O(g), ΔH = -245.5 kJ
• Given that the standard enthalpy of formation of NH₃ is -46.0 kJ mol⁻¹, and the enthalpy of formation of H₂ from gaseous atoms is -436 kJ mol⁻¹ while that of N₂ from gaseous atoms is -712 kJ mol⁻¹, what is the average N–H bond enthalpy in NH₃?
• For the spontaneous reaction 2C₂H₆(g) + 25O₂(g) → 16CO₂(g) + 18H₂O(g), what are the signs of ΔH, ΔS and ΔG in that order?
• The enthalpy changes for these reactions are given: 1/2 H2(g) + 1/2 O2(g) → OH(g); ΔH = 42.09 kJ mol⁻¹ H2(g) → 2H(g); ΔH = 435.89 kJ mol⁻¹ O2(g) → 2O(g); ΔH = 495.05 kJ mol⁻¹ Using this data, determine the O–H bond energy in the hydroxyl radical.
• The enthalpy of combustion of carbon to form carbon dioxide is −393.5 kJ per mole. What is the heat evolved when 35.2 g of CO₂ is produced from carbon and oxygen gas?
• For a reaction with ΔH = 35.5 kJ mol⁻¹ and ΔS = 83.6 J K⁻¹ mol⁻¹, at what temperature condition will the reaction be spontaneous? (Assume ΔH and ΔS remain constant with temperature.)

⚔️ Practice JEE Main Chemistry free + battle 1v1 →