Question

For the reaction
C₃H₈(g) + 5O₂(g)®3CO₂(g) + 4H₂O(l)
at constant temperature, ∆H – ∆E is
(a) – RT (b) + RT
(c) – 3 RT (d) + 3 RT

Answer 1

answer : option (b) -3RT

For the reaction

C₃H₈(g) + 5O₂(g) ⇒ 3CO₂(g) + 4H₂O(l)

from first law of thermodynamics,

∆H = W + ∆E

⇒ ∆H = ∆n_gRT + ∆E

∆H - ∆E = ∆n_g RT

where ∆n_g = number of moles of gaseous

products - number of moles of gaseous reactants

so, ∆n_g = 3 - (1 + 5) = -3 [ here CO2 is gaseous in products and O2 , C3H8 are gaseous molecules in reactants. so, put number of moles of these ]

so, ∆H - ∆E = -3RT

hence option (c) is correct choice.

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