The heat of combustion of ethanol into carbon dioxide and water is -327 kcal at constant pressure. The heat evolved (in cal) at constant volume and 27° C (if all gases behave ideally) is ( R =2. cal . mol -1 K -1)

Question

The heat of combustion of ethanol into carbon dioxide and water is -327 kcal at constant pressure. The heat evolved (in cal) at constant volume and 27° C (if all gases behave ideally) is ( R =2. cal . mol -1 K -1) (A)  (B)  (C)  (D)

Tardigrade Admin · Accepted Answer

C 2 H 5 OH (ℓ)+3 O 2( g ) longrightarrow 2 CO 2( g )+3 H 2 O (ℓ) Δ n g =2-3=-1 Δ c H =Δ c U +(Δ n g ) RT Δ c H =Δ c U - RT Δ c U =Δ c H + RT =-327 × 103+2 × 300 =-326400 cal . ∴ Heat evolved =326400 cal.

Q. The heat of combustion of ethanol into carbon dioxide and water is $- 327$ kcal at constant pressure. The heat evolved (in cal) at constant volume and $2 7^{\circ} C$ (if all gases behave ideally) is $(R = 2$ cal $m o l^{- 1} K^{- 1})$

$C_{2} H_{5} O H_{(ℓ)} + 3 O_{2 (g)} ⟶ 2 C O_{2 (g)} + 3 H_{2} O_{(ℓ)}$

$Δ n_{g} = 2 - 3 = - 1$

$Δ_{c} H = Δ_{c} U + (Δ n_{g}) RT$

$Δ_{c} H = Δ_{c} U - RT$

$Δ_{c} U = Δ_{c} H + RT$

$= - 327 \times 1 0^{3} + 2 \times 300$

$= - 326400 c a l .$

$∴$ Heat evolved

$= 326400$ cal.

Q. The heat of combustion of ethanol into carbon dioxide and water is −327 kcal at constant pressure. The heat evolved (in cal) at constant volume and 27∘C (if all gases behave ideally) is (R=2 cal mol−1K−1)

C2​H5​OH(ℓ)​+3O2(g)​⟶2CO2(g)​+3H2​O(ℓ)​ Δng​=2−3=−1 Δc​H=Δc​U+(Δng​)RT Δc​H=Δc​U−RT Δc​U=Δc​H+RT =−327×103+2×300 =−326400cal. ∴ Heat evolved =326400 cal.

Q. The heat of combustion of ethanol into carbon dioxide and water is $- 327$ kcal at constant pressure. The heat evolved (in cal) at constant volume and $2 7^{\circ} C$ (if all gases behave ideally) is $(R = 2$ cal $m o l^{- 1} K^{- 1})$

$C_{2} H_{5} O H_{(ℓ)} + 3 O_{2 (g)} ⟶ 2 C O_{2 (g)} + 3 H_{2} O_{(ℓ)}$

$Δ n_{g} = 2 - 3 = - 1$

$Δ_{c} H = Δ_{c} U + (Δ n_{g}) RT$

$Δ_{c} H = Δ_{c} U - RT$

$Δ_{c} U = Δ_{c} H + RT$

$= - 327 \times 1 0^{3} + 2 \times 300$

$= - 326400 c a l .$

$∴$ Heat evolved

$= 326400$ cal.