How do airbags work chemistry

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The following video shows how fast an airbag will expand! This entry was posted in Admin , Health , News and tagged Air bag , car. Click the blue button below to download QuickTime 4. When the car undergoes a head-on collision, a series of three chemical reactions inside the gas generator produce gas N 2 to fill the airbag and convert NaN 3 , which is highly toxic The maximum concentration of NaN 3 allowed in the workplace is 0.

The signal from the deceleration sensor ignites the gas-generator mixture by an electrical impulse, creating the high-temperature condition necessary for NaN 3 to decompose.

The nitrogen gas that is generated then fills the airbag. The purpose of the KNO 3 and SiO 2 is to remove the sodium metal which is highly reactive and potentially explosive, as you recall from the Periodic Properties Experiment by converting it to a harmless material.

The N 2 generated in this second reaction also fills the airbag, and the metal oxides react with silicon dioxide SiO 2 in a final reaction to produce silicate glass, which is harmless and stable. First-period metal oxides, such as Na 2 O and K 2 O, are highly reactive, so it would be unsafe to allow them to be the end product of the airbag detonation.

This table summarizes the species involved in the chemical reactions in the gas generator of an airbag. Nitrogen is an inert gas whose behavior can be approximated as an ideal gas at the temperature and pressure of the inflating airbag. Thus, the ideal-gas law provides a good approximation of the relationship between the pressure and volume of the airbag, and the amount of N 2 it contains. A certain pressure is required to fill the airbag within milliseconds.

Once this pressure has been determined, the ideal-gas law can be used to calculate the amount of N 2 that must be generated to fill the airbag to this pressure. The amount of NaN 3 in the gas generator is then carefully chosen to generate this exact amount of N 2 gas. An estimate for the pressure required to fill the airbag in milliseconds can be obtained by simple mechanical analysis.

Assume the front face of the airbag begins at rest i. Note: In the calculation below, we are assuming that the airbag is supported in the back i. Note: The pressure calculated is gauge pressure. The amount of gas needed to fill the airbag at this pressure is then computed by the ideal-gas law see Questions below. Note: the pressure used in the ideal gas equation is absolute pressure. When N 2 generation stops, gas molecules escape the bag through vents. T he pressure inside the bag decreases and the bag deflates slightly to create a soft cushion.

By 2 seconds after the initial impact, the pressure inside the bag has reached atmospheric pressure. Thus far, we have only considered the macroscopic properties i. Now we turn to a theoretical model to explain these macroscopic properties in terms of the microscopic behavior of gas molecules. The kinetic theory of gases assumes that gases are ideal i. In a microscopic view, the pressure exerted on the walls of the container is the result of molecules colliding with the walls, and hence exerting force on the walls Figure 3.

When many molecules hit the wall, a large force is distributed over the surface of the wall. This aggregate force, divided by the surface area, gives the pressure. This is a schematic diagram showing gas molecules purple in a container. The molecules are constantly moving in random directions. When a molecule hits the container wall green , it exerts a tiny force on the wall.

The sum of these tiny forces, divided by the interior surface area of the container, is the pressure. An important relationship derived from the kinetic theory of gases shows that the average kinetic energy of the gas molecules depends only on the temperature.

Thus, we can view temperature as a measure of the random motion of the particles, defined by the molecular speeds. We see from the kinetic theory of gases that temperature is related to the average speed of the molecules. This implies that there must be a range distribution of speeds for the system. In fact, there is a typical distribution of molecular speeds for molecules of a given molecular weight at a given temperature, known as the Maxwell-Boltzmann distribution Figure 4.

This distribution was first predicted using the kinetic theory of gases, and was then verified experimentally using a time-of-flight spectrometer. As shown by the Maxwell-Boltzmann distributions in Figure 4, there are very few molecules traveling at very low or at very high speeds. The maximum of the Maxwell-Boltzmann distribution is an intermediate speed at which the largest number of molecules are traveling.

As the temperature increases, the number of molecules that are traveling at high speeds increases, and the speeds become more evenly distributed i.