Which of the following reaction defines Δ Hfo?

Question

Which of the following reaction defines Δ Hfo?  (A)  C(diamond)+O2(g) xrightarrowCO2(g)  (B)  (1/2)H2(g)+(1/2)F2(g) xrightarrowHF(g)  (C)  N2(g)+3H2(g) xrightarrow2NH3(g)  (D)  CO(g)+(1/2)O2(g) xrightarrowCO2(g)

Tardigrade Admin · Accepted Answer

Δ Hfo is the enthalpy change when 1 mol of the substance is formed from its elements in the standard state. Reaction (a) does not represent Δ Hfo because standard state of carbon is graphite and not diamond.

Q. Which of the following reaction defines $Δ H_{f}^{o} ?$

$C_{(d iam o n d)} + O_{2} (g) C O_{2} (g)$

$\frac{1}{2} H_{2} (g) + \frac{1}{2} F_{2} (g) H F (g)$

$N_{2} (g) + 3 H_{2} (g) 2 N H_{3} (g)$

$CO (g) + \frac{1}{2} O_{2} (g) C O_{2} (g)$

$Δ H_{f}^{o}$ is the enthalpy change when 1 mol of the substance is formed from its elements in the standard state. Reaction (a) does not represent $Δ H_{f}^{o}$ because standard state of carbon is graphite and not diamond.

Q. Which of the following reaction defines ΔHfo​?

C(diamond)​+O2​(g)​CO2​(g)

21​H2​(g)+21​F2​(g)​HF(g)

N2​(g)+3H2​(g)​2NH3​(g)

CO(g)+21​O2​(g)​CO2​(g)