Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Thermodynamics question

2017 · 8 Apr · Shift 1 · Q23
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Chemistry
  4. /Thermodynamics
  5. /2017 · 8 Apr · Shift 1 · Q23

Thermodynamics question

2017 · 8 Apr · Shift 1 · Q23

JEE MainChemistryThermodynamicsMCQ+4 / −1
For a reaction, A(g) →\to→ A(ℓ\ellℓ); Δ\DeltaΔ H= −-− 3RT. The correct statement for the reaction is :
  1. A
    Δ\DeltaΔ H = Δ\DeltaΔ U eee O
  2. B
    Δ\DeltaΔ H = Δ\DeltaΔ U = O
  3. C
    ∣\left| {} \right.∣Δ\DeltaΔ H ∣\left| {} \right.∣ <∣\left| {} \right.∣ Δ\DeltaΔ U ∣\left| {} \right.∣
  4. D
    ∣\left| {} \right.∣Δ\DeltaΔ H ∣\left| {} \right.∣ >∣\left| {} \right.∣ Δ\DeltaΔ U ∣\left| {} \right.∣
View written solutionFree

Correct answer: D

  1. For reactions involving gases, the relation between enthalpy change and internal energy change is:
ΔH=ΔU+ΔngRT\Delta H = \Delta U + \Delta n_g RTΔH=ΔU+Δng​RT

where Δng=\Delta n_g =Δng​= moles of gaseous products −-− moles of gaseous reactants.

  1. Given reaction:
A(g)→A(ℓ)A(g) \to A(\ell)A(g)→A(ℓ)

Here,

  • gaseous products =0= 0=0
  • gaseous reactants =1= 1=1

So,

Δng=0−1=−1\Delta n_g = 0 - 1 = -1Δng​=0−1=−1
  1. Substitute into the formula:
ΔH=ΔU−RT\Delta H = \Delta U - RTΔH=ΔU−RT

Hence,

ΔU=ΔH+RT\Delta U = \Delta H + RTΔU=ΔH+RT
  1. Given:
ΔH=−3RT\Delta H = -3RTΔH=−3RT

Therefore,

ΔU=−3RT+RT=−2RT\Delta U = -3RT + RT = -2RTΔU=−3RT+RT=−2RT
  1. Compare magnitudes:
∣ΔH∣=3RT|\Delta H| = 3RT∣ΔH∣=3RT

and

∣ΔU∣=2RT|\Delta U| = 2RT∣ΔU∣=2RT

Thus,

∣ΔH∣>∣ΔU∣|\Delta H| > |\Delta U|∣ΔH∣>∣ΔU∣
  1. Check options:
  • A: ΔH=ΔU≠0\Delta H = \Delta U \ne 0ΔH=ΔU=0 ❌
  • B: ΔH=ΔU=0\Delta H = \Delta U = 0ΔH=ΔU=0 ❌
  • C: ∣ΔH∣<∣ΔU∣|\Delta H| < |\Delta U|∣ΔH∣<∣ΔU∣ ❌
  • D: ∣ΔH∣>∣ΔU∣|\Delta H| > |\Delta U|∣ΔH∣>∣ΔU∣ ✅

Therefore, the correct option is D.

PreviousNext

More from Thermodynamics

  • A gas undergoes change from state A to state B. In this process, the heat absorbed and work done by the gas is 5 J and 8 J, respectively. Now gas is brought back to A by another process during which 3 J of heat is evolved. In this reverse…2017 · MCQ
  • An ideal gas undergoes isothermal expansion at constant pressure. During the process :2017 · MCQ
  • Given, C(graphite)​+O2​→CO2​(g); Δr​Ho= - 393.5 kJ mol-1 H2​(g)+21​O2​(g)→H2​O(l)Δr​Ho= - 285.8 kJ mol-1 CO2​(g)+2H2​O(l)→CH4​(g)+2O2​(g)Δr​Ho…2017 · MCQ
  • Δ U is equal to :2017 · MCQ
  • For the reaction, A(g) + B(g) → C(g) + D(g), Δ Ho and Δ So are, respectively, − 29.8 kJ mol−1 and −0.100 kJ K−1 mol−1 at 298 K. The equilibrium constant for the reaction at 298 K is :2016 · MCQ
  • A reaction at 1 bar is non-spontaneous at low temperature but becomes spontaneous at high temperature. Identify the correct statement about the reaction among the following :2016 · MCQ
  • The plot shows the variation of −ln Kp versus temperature for the two reactions. M(s) +21​ O2​(g) → MO(s) and C(s) +21​ O2​(g) → CO(s) Identify the correct statement : Includes diagram2016 · MCQ
  • If 100 mole of H2​O2​ decompose at 1 bar and 300 K, the work done (kJ) by one mole of O2​(g) as it expands against 1 bar pressure is : 2H2​O2​(l) ⇌ 2H2​O(l) + O2​(g) (R = 8.3 J K − 1 mol − 1)2016 · MCQ