Question

The air bags that provide protection in autos 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?

Short answer

In the rapid chemical reaction occurring in an airbag, gases are produced, causing the airbag to expand. This expansion process results in the system (chemical reactants) transferring heat to the surroundings (airbag), yielding a positive heat flow (\(q > 0\)). Meanwhile, the system loses energy doing work on the surroundings (expanding the airbag), resulting in a negative work value (\(w < 0\)).

Step-by-step solution

Identify the process (expansion or compression)

In an airbag's chemical reaction, gases are produced from the reaction between sodium azide and metal oxide. The increased pressure causes the airbag to expand, which means that the system (chemical reactants) is doing work on the surroundings (airbag). This is an expansion process.

Heat (q) sign determination

In this reaction, heat is mostly generated. Since the system (chemical reactants) is transferring heat to the surroundings (airbag), the heat flow (q) will be positive.

Work (w) sign determination

Since we identified that the system is expanding, the work done (w) is negative because the system loses energy doing work on the surroundings (expanding the airbag). Thus, the work (w) has a negative sign.

Conclusion

For this rapid chemical reaction in airbags, the signs of heat (q) and work (w) can be concluded as follows: \(q > 0\) and \(w < 0\).