Question

For which one of the following equations is $\vartriangle {H^ \circ }_{reaction}$ equal to $\Delta H_f^ \circ $ for the product?
A. ${N_2} + {O_3} \to {N_2}{O_3}$
B. $C{H_4} + 2C{l_2} \to C{H_2}C{l_2} + 2HCl$
C. $Xe + 2{F_2} \to Xe{F_4}$
D. $2CO + {O_2} \to 2C{O_2}$

Answer 1

Hint: The standard state of a material is a reference point for the material’s thermodynamic state properties such as enthalpy, entropy, Gibbs free energy etc. It is used to calculate the material’s properties under different conditions and is denoted as $H_f^ - $ . The standard state for a gas is the hypothetical state 1bar for liquids and solids the pure substance at 1 bar for elements the most stable allotrope of the element and for a substance in solution concentration at 1 M and 1 bar.

Complete answer:
The formation of heat is defined by the heat generated when the compound formed and its component elements form in standard state. Due to this definition, B and D are not correct and the starting material is compound.
Here A is not the correct answer. ozone is not the correct standard state of oxygen.

Hence, option (C) is the correct answer.

Note: The enthalpy change that occurs during catalytic hydrogenation. Used to compare stability of pi-bond molecules and as a probe of alkene stability alkyne stability, conjugation and aromaticity. Heat of hydrogenation of an alkene is the standard enthalpy of catalytic hydrogenation of an alkene. Catalytic hydrogenation of an alkene is always exothermic. Therefore, the heat of hydrogenation of alkenes is always negative. The least stable alkene will have either least highly substituted double bond. The least stable alkene will have the highest heat of hydrogenation which is defined by enthalpy.