Problem 99 - Chemistry: The Central Science in SI Units, Global Edition

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

In the rapid chemical reaction that causes the airbags to expand, heat is released from the system (chemical reactants) to the surroundings (airbags), resulting in a positive sign for the heat transfer (q). Additionally, work is done by the system on the surroundings as the gas produced exerts pressure on the airbags to expand, leading to a positive sign for the work done (w). Therefore, the expected signs are: \(q > 0\) and \(w > 0\).

Step 1: The Sign of Heat Transfer (q)

During the rapid chemical reaction in the airbags, gas is produced that causes the airbags to inflate. The conversion of reactants into products usually releases energy in the form of heat (exothermic reaction). Therefore, we expect a positive sign for "q" as heat is being transferred from the system (chemical reactants) to the surroundings (the airbags).

Step 2: The Sign of Work Done (w)

When the airbags expand, the gas produced during the reaction exerts pressure on the surroundings (the airbags' interior). This means that the gas expansion causes work to be done on the surroundings as the pressure is applied from within the system, pushing the airbags to expand. In this case, the sign of "w" will be positive, as work is done by the system (chemical reactants) to the surroundings (airbags). #Summary# In conclusion, for the rapid chemical reaction that occurs in the automobile airbags during an accident, the expected signs are: 1. Heat Transfer (q): Positive 2. Work Done (w): Positive

Key Concepts

Chemical reactions

Chemical reactions form the foundation of many processes in both everyday life and scientific applications. During a chemical reaction, reactants are transformed into products, often resulting in observable physical changes, energy transformations, or new material formations. The transformation involves the breaking and forming of bonds between atoms.

Key points about chemical reactions include:

• **Energy change:** Reactions can either absorb or release energy. This is crucial in determining whether a reaction is exothermic or endothermic, affecting the temperature of the surroundings.
• **Efficiency:** Some reactions are designed to happen rapidly, like in airbags, to ensure safety during collisions.
• **Reversibility:** Many reactions are reversible, but others, such as combustion, progress to completion in one direction.

In the case of automobile airbags, the chemical reaction is engineered to be rapid and reliable, transforming a solid compound into gas, ensuring immediate inflation.

Exothermic reactions

Exothermic reactions are a type of chemical reaction where energy is released into the surroundings, usually in the form of heat. This release occurs because the energy required to break the bonds in the reactants is less than the energy released when new bonds form in the products.

Some essential characteristics of exothermic reactions include:

• **Heat release:** The system releases heat, warming the surroundings. This is why the heat transfer, denoted by "q," is positive in exothermic processes.
• **Spontaneity:** Many exothermic reactions occur spontaneously because they often lead to lower energy states and increased stability.
• **Examples:** Combustion, respiration, and this airbag deployment reaction.

The rapid inflation of airbags is due to an exothermic reaction that produces nitrogen gas, swiftly filling the airbag and cushioning impacts.

Gas expansion

Gas expansion is a fundamental concept where gas particles spread out to occupy a larger volume. The expansion occurs because gas particles have kinetic energy, causing them to move rapidly and push against their containment, such as the interior walls of an airbag.

In scenarios like airbag deployment, gas expansion is key and has the following characteristics:

• **Work done:** The gas does work on its surroundings by pushing against the airbag material, causing it to expand. This is represented by the positive sign for work "w."
• **Adaptive volume:** Gases naturally expand to fill their containers, meaning that if an airbag is its container, it will inflate fully until balanced by external pressures.
• **Speed of process:** In airbags, this expansion is designed to be exceptionally rapid, ensuring immediate protection in an accident.

Overall, gas expansion facilitates converting chemical energy to mechanical work, ensuring the airbag deploys promptly to cushion any impact.