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Thermodynamics question

2023 · 13 Apr · Shift 2 · Q1
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Thermodynamics question

2023 · 13 Apr · Shift 2 · Q1

JEE MainChemistryThermodynamicsMCQ+4 / −1
What happens when methane undergoes combustion in systems A and B respectively? JEE Main 2023 (Online) 13th April Evening Shift Chemistry - Thermodynamics Question 65 English
  1. A
    System A System B
    Temperature falls Temperature rises
  2. B
    System A System B
    Temperature rises Temperature remains same
  3. C
    System A System B
    Temperature falls Temperature remains same
  4. D
    System A System B
    Temperature remains same Temperature rises
View written solutionFree

Correct answer: B

  1. Nature of methane combustion

    Methane burns according to CH4+2O2→CO2+2H2O+heat\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + heat}CH4​+2O2​→CO2​+2H2​O+heat

    This is an exothermic process, so heat is released.

  2. Interpretation of systems A and B

    In such thermodynamics questions, the two systems usually represent:

    • System A: an adiabatic system (no heat exchanged with surroundings)
    • System B: an isothermal system (temperature kept constant by exchange of heat with surroundings)

  3. Effect in System A

    Since combustion releases heat and in an adiabatic system that heat cannot escape, the heat remains within the system.

    Therefore, the temperature rises.

  4. Effect in System B

    In an isothermal system, temperature is maintained constant by transferring the released heat to surroundings.

    Therefore, the temperature remains the same.

  5. Evaluate options

    • A: System A falls, System B rises — incorrect
    • B: System A rises, System B remains same — correct
    • C: System A falls, System B remains same — incorrect
    • D: System A remains same, System B rises — incorrect

  6. Final answer

    The correct option is B\boxed{\text{B}}B​

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