How it applies to our lives

Understanding chemical reactions explains how everyday items like soaps, antacids, batteries, and the airbag in your car work. A big part of AP Chemistry is that you are required to observe electron transfer, assign oxidation numbers, and balance equations. This all happens around us daily, specifically in the life saving item in your car, your air bags. A car airbag is like a super-fast balloon filled by a chemical reaction. When a car crashes, the airbag inflates to make sure there are no serious injuries. Here is how chemistry does that. Inside the steering wheel, there is no trapped air. Instead, there is just a small handful of a white powder called sodium azide and when the sensors detect a crash, they shoot a tiny electric spark into that powder. (Because sodium azide is highly toxic, the inflator also contains chemicals like potassium nitrate and silica. These react with the sodium to turn it into harmless glass.) The heat from that spark causes a sudden chemical change. In just seconds, the solid powder violently splits apart and transforms into a massive cloud of nitrogen gas. This is a prime example of an exothermic reaction taking place in real time to potentially save a life. There is another extremely significant part of this. If the engineers put too little powder in the wheel, the bag will be floppy, and you will hit the dashboard. And if they put too much powder, the bag will inflate like a bomb and hurt you. Engineers must calculate the exact weight of the powder so that it creates just enough gas to fill the bag perfectly—not too hard, and not too soft.