The difference between the heat change at constant pressure and that at constant volume for the combustion of 46 g of ethanol at 27° C is

Question

The difference between the heat change at constant pressure and that at constant volume for the combustion of 46 g of ethanol at 27° C is (A) -4.59 kJ (B) +4.59 kJ (C) +2.49 kJ (D) -2.49 kJ

Tardigrade Admin · Accepted Answer

C 2 H 5 OH (l)+3 O 2(g) arrow 2 CO 2(g)+3 H 2 O (g) ; Δ n(g)=2-3=-1 qp-qv=Δ ng R T=(-1) × 8.314 × 300= -2.49 kJ

Q. The difference between the heat change at constant pressure and that at constant volume for the combustion of $46 g$ of ethanol at $2 7^{\circ} C$ is

$- 4.59 k J$

$+ 4.59 k J$

$+ 2.49 k J$

$- 2.49 k J$

$C_{2} H_{5} O H_{(l)} + 3 O_{2 (g)} \to 2 C O_{2 (g)} + 3 H_{2} O_{(g)}; Δ n_{(g)} = 2 - 3 = - 1$

$q_{p} - q_{v} = Δ n_{g} RT = (- 1) \times 8.314 \times 300 = - 2.49 k J$

Q. The difference between the heat change at constant pressure and that at constant volume for the combustion of 46g of ethanol at 27∘C is

−4.59kJ

+4.59kJ

+2.49kJ

−2.49kJ