Calcium carbide, CaC2, is manufactured by the reaction of...

Calcium carbide, $\mathrm{CaC}_{2}$, is manufactured by the reaction of CaO with carbon at a high temperature. (Calcium carbide is then used to make acetylene. $\mathrm{CaO}(\mathrm{s})+3 \mathrm{C}(\mathrm{s}) \rightarrow \mathrm{CaC}_{2}(\mathrm{s})+\mathrm{CO}(\mathrm{g})$ $$ \Delta_{1} H^{\circ}=+464.8 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn} $$ Is this reaction endothermic or exothermic? What is the enthalpy change if $10.0 \mathrm{g}$ of $\mathrm{CaO}$ is allowed to react with an excess of carbon?

Calcium carbide, $\mathrm{CaC}_{2}$, is manufactured by the reaction of CaO with carbon at a high temperature. (Calcium carbide is then used to make acetylene. $\mathrm{CaO}(\mathrm{s})+3 \mathrm{C}(\mathrm{s}) \rightarrow \mathrm{CaC}_{2}(\mathrm{s})+\mathrm{CO}(\mathrm{g})$
$$
\Delta_{1} H^{\circ}=+464.8 \mathrm{kJ} / \mathrm{mol}-\mathrm{rxn}
$$
Is this reaction endothermic or exothermic? What is the enthalpy change if $10.0 \mathrm{g}$ of $\mathrm{CaO}$ is allowed to react with an excess of carbon?

Key Concepts

Exothermic vs Endothermic Reactions

This concept involves determining whether a reaction absorbs or releases heat. In chemical thermodynamics, a reaction is classified as endothermic if it absorbs heat from its surroundings (indicated by a positive ?H), and exothermic if it releases heat (indicated by a negative ?H). Recognizing the sign of ?H helps in understanding the nature of the heat flow during a reaction.

Reaction Enthalpy

Reaction enthalpy is the heat change associated with a chemical reaction at constant pressure, typically given in kilojoules per mole (kJ/mol). It represents the energy difference between products and reactants. When provided in a balanced equation, it allows for the calculation of the total energy change when scaling the reaction to non?stoichiometric amounts of reactants.

Stoichiometry

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It enables the conversion of a given mass of a reactant to moles using its molar mass, and then links these moles to the energy change indicated by the reaction enthalpy. This conversion process is crucial for calculating the energy change corresponding to specific amounts of substances.

Limiting Reactant

The concept of the limiting reactant is central when one reactant is present in smaller stoichiometric amount than required to completely react with other reactants. It determines the extent of the reaction and, consequently, the total enthalpy change. When one reactant is in excess, calculations focus on the reactant that limits the reaction to compute the actual energy released or absorbed.

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