Chemistry - Thermochemistry Question with Solution | TestHub
ChemistryThermochemistryEnthalpy of CombustionHard2 minQB
ChemistryHardstatement
Statement 1: For the reaction N2(g) + 3H2(g) → 2NH3(g) at a given temperature, |ΔH| > |ΔU|.
Statement 2: ΔH = ΔU + Δng RT; here Δng = -2 and ΔH < 0, so ΔU is less negative than ΔH.
Options:
Answer:
A
Solution:
Δng = 2 - 4 = -2, so ΔU = ΔH - Δng RT = ΔH + 2RT. Since the synthesis of ammonia is exothermic, adding 2RT makes ΔU less negative than ΔH, giving |ΔH| > |ΔU| (Statement 1 correct). Statement 2 carries out exactly this sign analysis and is the correct explanation. The trap is assuming contraction of gas moles always makes |ΔH| < |ΔU|; the sign of ΔH matters. Ans: (a).
Stream:JEESubject:ChemistryTopic:ThermochemistrySubtopic:Enthalpy of Combustion
⏱ 2mℹ️ Source: QB
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