Enthalpy Changes Nitrogen monoxide, a gas recently found to...

Enthalpy Changes Nitrogen monoxide, a gas recently found to be involved in a wide range of biological processes, reacts with oxygen to give brown $\mathrm{NO}_{2}$ gas. $$ \begin{aligned} 2 \mathrm{NO}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow & 2 \mathrm{NO}_{2}(\mathrm{g}) \\ \Delta_{r} H^{\circ} &=-114.1 \mathrm{kJ} / \mathrm{mol}-\mathrm{pxn} \end{aligned} $$ Is this reaction endothermic or exothermic? What is the enthalpy change if $1.25 \mathrm{g}$ of $\mathrm{NO}$ is converted completely to $\mathrm{NO}_{2} ?$

Enthalpy Changes
Nitrogen monoxide, a gas recently found to be involved in a wide range of biological processes, reacts with oxygen to give brown $\mathrm{NO}_{2}$ gas.
$$
\begin{aligned}
2 \mathrm{NO}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow & 2 \mathrm{NO}_{2}(\mathrm{g}) \\
\Delta_{r} H^{\circ} &=-114.1 \mathrm{kJ} / \mathrm{mol}-\mathrm{pxn}
\end{aligned}
$$
Is this reaction endothermic or exothermic? What is the enthalpy change if $1.25 \mathrm{g}$ of $\mathrm{NO}$ is converted completely to $\mathrm{NO}_{2} ?$

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Key Concepts

Stoichiometry of Chemical Reactions

Stoichiometry involves using the balanced chemical equation to determine the relative quantities of reactants and products. It enables the calculation of how much energy is involved per mole of reactions, facilitating the scaling of the enthalpy change to different amounts of substances.

Mole Concept

The mole concept is essential for converting masses of chemical substances into amounts (in moles) using their molar masses. This conversion is necessary for relating given weight of reactants to the stoichiometrically defined reactions and associated energy changes.

Enthalpy Change

This concept refers to the overall heat content change during a chemical reaction occurring at constant pressure. It quantifies the energy absorbed or released by a system, and a negative value indicates that the reaction releases heat into its surroundings.

Exothermic vs Endothermic Reactions

This concept distinguishes reactions based on their heat exchange with the environment. Exothermic reactions release heat, resulting in a negative enthalpy change, whereas endothermic reactions absorb heat, leading to a positive enthalpy change.

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