Question

Which of the following is an endothermic process? a. combustion of gasoline in a car engine b. sublimation of carbon dioxide; \(\mathrm{CO}_{2}(s) \rightarrow \mathrm{CO}_{2}(g)\) c. water condensing on a cold pipe d. freezing juice to make popsicles

Short answer

The endothermic process among the given options is \(b. \mathrm{CO}_{2}(s) \rightarrow \mathrm{CO}_{2}(g)\), the sublimation of carbon dioxide, as it absorbs heat from the surroundings during the transition from solid to gas.

Step-by-step solution

Option a: combustion of gasoline in a car engine

Combustion of gasoline is a chemical reaction that releases heat. Therefore, it is an exothermic process, not endothermic.

Option b: sublimation of carbon dioxide

Sublimation is a process in which a substance transitions directly from a solid-state to a gaseous state without passing through the liquid state. In this case, carbon dioxide transitions from solid (\(\mathrm{CO}_{2}(s)\)) to gas (\(\mathrm{CO}_{2}(g)\)). For this to occur, the solid needs to absorb heat to gain enough energy to become a gas. Therefore, this process is endothermic.

Option c: water condensing on a cold pipe

When water condenses on a cold pipe, it means the water is transitioning from a gaseous state to a liquid state. In this process, it releases heat to the surroundings, which makes it an exothermic process, not endothermic.

Option d: freezing juice to make popsicles

Freezing juice to make popsicles involves the transition of a liquid to a solid-state. In this process, heat is released to the surroundings as the juice freezes. Therefore, this process is exothermic, not endothermic.

Conclusion

Among the given options, the only endothermic process is option b, sublimation of carbon dioxide (\(\mathrm{CO}_{2}(s) \rightarrow \mathrm{CO}_{2}(g)\)).

Key concepts

Combustion Reaction

Combustion reactions are chemical processes where a substance reacts quickly with oxygen to produce heat and light. In a combustion reaction, such as burning gasoline in a car engine, the fuel combusts to release energy. This energy typically comes in the form of heat, which is why combustion reactions are considered exothermic. In these reactions, the bonds in the fuel and oxygen molecules break, and new bonds form to create combustion products like carbon dioxide and water. Key characteristics of combustion include:

• Rapid reaction with oxygen
• Production of heat and light
• Exothermic nature

While combustion is central to energy production, it is not endothermic because it does not require an input of heat to proceed. Instead, it releases energy into the surrounding environment.

Sublimation

Sublimation is the process by which a solid changes directly to a gas without passing through the liquid state. This interesting process is endothermic because it requires the absorption of heat. Solid carbon dioxide, or dry ice, is a classic example. During sublimation,

• The solid particles gain enough energy to break their fixed positions.
• This requires an input of heat, absorbed from the surroundings.
• As the particles gain energy, they move more rapidly and spread out, forming a gas.

Sublimation being an endothermic process makes it crucial for certain industrial and scientific applications where controlled heat absorption is necessary. It highlights how energy can drive physical state changes.

Phase Transition

A phase transition is a change of a substance from one state of matter to another, such as solid to liquid, liquid to gas, and vice versa. These transitions can either be endothermic or exothermic depending on the direction of the change. For example, when a substance transitions from a solid to a liquid (melting) or from a liquid to a gas (vaporization), it absorbs heat from its surroundings, making these processes endothermic. Conversely, when substances transition from gas to liquid (condensation) or liquid to solid (freezing), they release heat, being exothermic in nature. Each phase transition involves:

• A specific amount of energy absorbed or released per mole of substance.
• Changes in particle arrangement and energy states.
• A constant temperature during the transition.

Understanding phase transitions helps in predicting how matter responds to changes in temperature and pressure, crucial for everything from weather forecasting to countless industrial processes.

Heat Absorption

Heat absorption occurs when a substance takes in energy from its surroundings. This energy or heat causes changes at the molecular level, such as increased motion or breaking of bonds. Endothermic processes, like sublimation, melting, and vaporization, involve heat absorption because they require this energy input to proceed. Some key points about heat absorption include:

• Required for overcoming forces maintaining the current state of matter.
• Promotes the movement of particles, leading to a change in physical state or chemical reaction.
• Can occur naturally (like ice melting in the sun) or be induced (such as in heating systems).

Recognizing the role of heat absorption assists in understanding how and why materials change form, and it underscores principles critical in fields like thermodynamics and energy management.