Classify each of the following as exothermic or endothermic...

Classify each of the following as exothermic or endothermic and give the $\Delta H$ for each: a. $\mathrm{C}_{3} \mathrm{H}_{8}(g)+5 \mathrm{O}_{2}(g) \stackrel{\Delta}{\longrightarrow} 3 \mathrm{CO}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)+2220 \mathrm{~kJ}$ b. $2 \mathrm{Na}(s)+\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{NaCl}(s)+819 \mathrm{~kJ}$ c. $\mathrm{PCl}_{5}(g)+67 \mathrm{~kJ} \longrightarrow \mathrm{PCl}_{3}(g)+\mathrm{Cl}_{2}(g)$

Classify each of the following as exothermic or endothermic and give the $\Delta H$ for each:
a. $\mathrm{C}_{3} \mathrm{H}_{8}(g)+5 \mathrm{O}_{2}(g) \stackrel{\Delta}{\longrightarrow} 3 \mathrm{CO}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)+2220 \mathrm{~kJ}$
b. $2 \mathrm{Na}(s)+\mathrm{Cl}_{2}(g) \longrightarrow 2 \mathrm{NaCl}(s)+819 \mathrm{~kJ}$
c. $\mathrm{PCl}_{5}(g)+67 \mathrm{~kJ} \longrightarrow \mathrm{PCl}_{3}(g)+\mathrm{Cl}_{2}(g)$

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Key Concepts

Endothermic Reaction

An endothermic reaction is one that absorbs heat from its environment. During such reactions, the reactants require energy input to convert into products, so the reaction mixture becomes colder. This is represented by a positive delta H value. Endothermic processes are key in understanding reaction spontaneity and energy flow in chemical systems.

Enthalpy Change (Delta H)

Enthalpy change, denoted as delta H, measures the total heat change during a chemical reaction at constant pressure. It is a crucial concept in thermodynamics and provides insight into whether a reaction is exothermic or endothermic. A negative delta H indicates heat release, while a positive value points to heat absorption, helping chemists predict reaction behavior and energy requirements.

Exothermic Reaction

An exothermic reaction is one that releases heat to its surroundings. In these reactions, the products have lower energy than the reactants, and the heat released is typically represented by a negative delta H value. Recognizing exothermic reactions is important in thermochemistry, as they often involve combustion or other processes where energy is given off.

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