The standard heats of formation of NO2( g) and N2 O4( g) are 8.0 and 2.0 kcal mol^-1, respective

step 1 Standard heats of formation of nitrous oxide and nitrous peroxide are 8 .0 and 2 .0 kilo cal per

The standard heats of formation of NO2( g) and N2 O4( g) are...

The standard heats of formation of $\mathrm{NO}_{2(\mathrm{~g})}$ and $\mathrm{N}_{2} \mathrm{O}_{4}(\mathrm{~g})$ are $8.0$ and $2.0 \mathrm{kcal} \mathrm{mol}^{-1}$, respectively. The
heat of dimcrization of $\mathrm{NO}_{2}$ in kcal is
(1) $10.0$
(2) $6.0$
(3) $12.0$
(4) $14.0$

Key Concepts

Hess's Law

Hess's law states that the total enthalpy change for a chemical reaction is independent of the reaction pathway. This means that the overall change in enthalpy can be determined by summing the heats of formation of products and subtracting the sum of the heats of formation of the reactants, making it a useful principle for calculating reaction enthalpies even when the reaction occurs in multiple steps.

Reaction Enthalpy Calculation

Reaction enthalpy calculation involves using the standard heats of formation of reactants and products to determine the overall heat change of a reaction. For a known reaction, such as the dimerization process, the enthalpy change can be computed by subtracting the sum of the formation enthalpies of the reactants from the sum of the formation enthalpies of the products, according to Hess’s law. This approach is essential for understanding exothermic and endothermic processes and for predicting the energy changes involved in chemical transformations.

Standard Heats of Formation

The standard heat of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states under standard conditions (usually 1 atm and 25°C). It is a fundamental concept in thermochemistry because it provides a reference point for calculating the enthalpy changes of chemical reactions through Hess’s law.

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