Question

Are the following processes exothermic or endothermic? a. the combustion of gasoline in a car engine b. water condensing on a cold pipe c. \(\mathrm{CO}_{2}(s) \longrightarrow \mathrm{CO}_{2}(g)\) d. \(\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{F}(g)\)

Short answer

a. The combustion of gasoline in a car engine is an exothermic process. b. Water condensing on a cold pipe is an exothermic process. c. \(CO_{2}(s) \longrightarrow CO_{2}(g)\) is an endothermic process. d. \(F_{2}(g) \longrightarrow 2 F(g)\) is an endothermic process.

Step-by-step solution

a. Combustion of gasoline in a car engine

Combustion is a chemical reaction that occurs between a fuel and an oxidant, producing heat and light in the form of a flame. In this process, the chemical potential energy stored within the gasoline is converted into thermal energy. Since heat is released during combustion, this process is exothermic.

b. Water condensing on a cold pipe

When water condenses, it changes from its gaseous state (water vapor) to its liquid state. This phase transition is accompanied by the release of energy in the form of heat. Therefore, the condensation of water on a cold pipe is an exothermic process.

c. CO2(s) → CO2(g)

The process described here is the sublimation of solid carbon dioxide (CO2) into gaseous carbon dioxide. During sublimation, energy is absorbed by the solid CO2 to break the intermolecular forces holding the solid structure together, resulting in a transition to the gaseous state. Thus, this process is endothermic because it requires an input of energy (heat) for the phase change to occur.

d. F2(g) → 2 F(g)

The given reaction represents the dissociation of a diatomic fluorine molecule (F2) into two separate fluorine atoms (F). Breaking the chemical bond between the two fluorine atoms requires an input of energy since chemical bonds store energy. Therefore, this process is endothermic.