The difference between Δ H and Δ U (Δ H- Δ U), when the combustion of one mole of heptane (I) is carried out at a temperature T, is equal to:

Question

The difference between Δ H and Δ U (Δ H- Δ U), when the combustion of one mole of heptane (I) is carried out at a temperature T, is equal to: (A) 3RT (B) - 3RT (C) -4 RT (D) 4RT

Tardigrade Admin · Accepted Answer

C 7 H 16(ℓ)+11 O 2( g ) longrightarrow 7 CO 2( g )+8 H 2 O (ℓ) Δ ng = np - nr =7-11=-4 ∵ Δ H=Δ U+Δ ng R T ∴ Δ H-Δ U=-4 R T

Q. The difference between $Δ H$ and $Δ U (Δ H - Δ U)$ , when the combustion of one mole of heptane (I) is carried out at a temperature $T$ , is equal to:

$3 RT$

$- 3 RT$

$- 4 RT$

$4 RT$

$C_{7} H_{16} (ℓ) + 11 O_{2} (g) ⟶ 7 C O_{2} (g) + 8 H_{2} O (ℓ)$
$Δ n g = n p - n r = 7 - 11 = - 4$
$∵ Δ H = Δ U + Δ n_{g} RT$
$∴ Δ H - Δ U = - 4 RT$

Q. The difference between ΔH and ΔU(ΔH−ΔU), when the combustion of one mole of heptane (I) is carried out at a temperature T, is equal to:

3RT

−3RT

−4RT

4RT