Problem 99 - Chemistry The Central Science In Si Units

Question

The air bags that provide protection in automobiles in the event of an accident expand because of a rapid chemical reaction. From the viewpoint of the chemical reactants as the system, what do you expect for the signs of \(q\) and \(w\) in this process?

Step-by-Step Solution

Answer

Both \(q\) and \(w\) are negative.

Step 1: Understanding the System

In the context of the airbag mechanism, the chemical reactions inside the airbag represent our system. These reactions are rapid and exothermic, meaning they release energy (heat) into the surroundings.

Step 2: Determine the Sign of Heat (q)

Since the chemical reactions are exothermic, energy in the form of heat is released from the system to the surroundings. Therefore, the heat flow, represented by \(q\), is negative \((q < 0)\).

Step 3: Determine the Sign of Work (w)

As the gas forms rapidly during the chemical reaction, it causes the airbag to expand by pushing against its surroundings (the lining of the airbag and the car interior). This expansion indicates that work is done by the system on the surroundings. Therefore, the work done, represented by \(w\), is negative \((w < 0)\) under the convention that positive work is done on the system.

Key Concepts

Exothermic Reactions

Exothermic reactions involve the release of energy, more often than not in the form of heat, to the surrounding environment. Within the context of an airbag deploying during an automobile accident, the chemicals inside the airbag undergo a rapid exothermic reaction.

This process typically involves the conversion of chemical energy into heat energy, which is then transferred to the surroundings. How can you tell if a reaction is exothermic? Here are a few indicators to look out for:

• Reduction in the amount of energy within the system since energy is emitted outward.
• Increase in temperature around the vicinity of the reaction, indicative of heat being expelled.
• From a chemical perspective, the products have lower potential energy compared to the reactants, signifying that energy has been released.

Understanding these elements can help clarify why the heat flow, represented by the variable \(q\), is negative \((q < 0)\) during this reaction. The system (the chemical reactants) loses heat to its environment, which is a defining trait of exothermic processes.

Heat Transfer in Chemistry

In thermochemistry, heat transfer plays an essential role as it dictates how energy moves between a system and its surroundings. Within an exothermic airbag reaction, the heat energy is actively transported from the reacting chemicals inside the airbag to the external environment.

Heat transfer can be characterized by different methods of movement:

• **Conduction** occurs when heat moves directly through materials, often seen in solids.
• **Convection** involves the movement of heat via fluids or gases, playing a role in airbag deployment where heated gases expand rapidly.
• **Radiation** transfers energy through electromagnetic waves, but plays a minor role in most chemical processes.

The principle of heat transfer is crucial for predicting the behavior of substances under varying temperature conditions. The directional flow of heat here means that the airbag system loses heat as the exothermic reaction progresses, reinforcing the negative sign of \(q\). The continuous loss and movement of heat are pivotal in understanding the dynamics of the airbag's response.

Work in Thermodynamic Processes

Work in the context of thermodynamic processes refers to the energy transferred when a force is applied over a distance. It is a critical component in understanding systems like airbag deployment, where rapid chemical reactions cause changes in volume. In these scenarios:

• The expansion of gas within the airbag illustrates work done by the system as it inflates.
• The surroundings, such as the car interior and airbag casing, experience the force of the expanding gas.
• By convention, this expansion involves work being done by the system on its surroundings, which makes \(w\) negative, since positive work is typically defined as work done on the system.

This energy transfer demonstrating work done underscores the mechanical aspects of thermochemical processes. Such processes are crucial in defining how systems like airbags perform under sudden impact conditions. The interplay between work and heat exchange illustrates how energy transformations facilitate real-world applications, ensuring safety in automotive technologies.