Q. 7.72 - An Introduction to General, Organic, and Biological Chemistry

Question

Classify each of the following as exothermic or endothermic: 

a. ${\mathrm{C}}_3{\mathrm{H}}_8 \left(\mathrm{g}\right) + 5{\mathrm{O}}_2 \left(\mathrm{g}\right)\stackrel{∆}{\to } 3{\mathrm{CO}}_2 \left(\mathrm{g}\right) + 4{\mathrm{H}}_2\mathrm{O} \left(\mathrm{g}\right) + 2220 \mathrm{kJ}$

b. $2 \mathrm{Na} \left(\mathrm{s}\right) +{\mathrm{Cl}}_2 \left(\mathrm{g}\right)\to 2 \mathrm{NaCl} \left(\mathrm{s}\right) + 819 \mathrm{kJ}$

c. ${\mathrm{PCl}}_5 \left(\mathrm{g}\right) + 67 \mathrm{kJ} \to {\mathrm{PCl}}_3 \left(\mathrm{g}\right) + {\mathrm{Cl}}_2 \left(\mathrm{g}\right)$

Step-by-Step Solution

Answer

a. It is an exothermic reaction. 

b. It is an exothermic reaction. 

c. It is an endothermic reaction. 

Part(a) Step 1: Given information

We have been given the equation :

${\mathrm{C}}_3{\mathrm{H}}_8 \left(\mathrm{g}\right) + 5{\mathrm{O}}_2 \left(\mathrm{g}\right)\stackrel{∆}{\to } 3{\mathrm{CO}}_2 \left(\mathrm{g}\right) +\hspace{0.17em}4{\mathrm{H}}_2\mathrm{O} \left(\mathrm{g}\right) + 2220 \mathrm{kJ}$

We need to find out whether it is exothermic reaction or endothermic reaction.

Part(a) Step 2: Explanation

Exothermic processes produce heat, which raises the temperature of the immediate environment. Endothermic processes absorb heat from the environment and chill it. In exothermic reaction, heat is at product side while in endothermic reaction, heat is at reactant side.

Hence, the reaction ${\mathrm{C}}_3{\mathrm{H}}_8 \left(\mathrm{g}\right) + 5{\mathrm{O}}_2\stackrel{∆}{\to }3{\mathrm{CO}}_2 \left(\mathrm{g}\right) + 4{\mathrm{H}}_2\mathrm{O} \left(\mathrm{g}\right) + 2220 \mathrm{kJ}$ is exothermic reaction.

Part(b) Step 1: Given information

We have been given the equation :
$2\mathrm{Na} \left(\mathrm{s}\right) + {\mathrm{Cl}}_2 \left(\mathrm{g}\right)\to 2\mathrm{NaCl} \left(\mathrm{s}\right) + 819 \mathrm{kJ}$

We need to find out whether it is exothermic reaction or endothermic reaction.

Part(b) Step 2: Explanation

Exothermic processes produce heat, which raises the temperature of the immediate environment. Endothermic processes absorb heat from the environment and chill it. In exothermic reaction, heat is at product side while in endothermic reaction, heat is at reactant side.

Hence, the reaction $2\mathrm{Na} \left(\mathrm{s}\right) +{\mathrm{Cl}}_2 \left(\mathrm{g}\right)\to 2\mathrm{NaCl} \left(\mathrm{s}\right) + 819 \mathrm{kJ}$ is exothermic reaction.

Part(c) Step 1: Given information

We have been given the equation :

${\mathrm{PCl}}_5 \left(\mathrm{g}\right) + 67 \mathrm{kJ}\to {\mathrm{PCl}}_3 \left(\mathrm{g}\right) + {\mathrm{Cl}}_2 \left(\mathrm{g}\right)$

We need to find out whether it is exothermic reaction or endothermic reaction.

Part(c) Step 2: Explanation

Exothermic processes produce heat, which raises the temperature of the immediate environment. Endothermic processes absorb heat from the environment and chill it. In exothermic reaction, heat is at product side while in endothermic reaction, heat is at reactant side.

Hence, the reaction ${\mathrm{PCl}}_5 \left(\mathrm{g}\right) + 67 \mathrm{kJ}\to {\mathrm{PCl}}_3 \left(\mathrm{g}\right) + {\mathrm{Cl}}_2 \left(\mathrm{g}\right)$ is endothermic reaction.