Sitting around the fire, making smores or warming up to a mug of hot chocolate is a favorite pastime for many. But, do you ever stop to think about how that fire is actually made? How about driving your car? You know gas makes it go, but how? Both are thanks to the processes of combustion and energy release. Learn more about how combustion and energy release work in our everyday lives.
My husband is an auto-mechanic, and in our house, we talk shop.
Speaking with my husband teaches me a lot about how science has been applied to create modern marvels like automobiles that have made our lives more convenient.
In order for you to drive your car, you know that it needs fuel, and this is why you head to the gas station probably once a week.
But, how does gasoline provide the energy needed to make your car move?
What is the chemistry behind it?
For those of us who drive a standard gasoline-fueled car, the gasoline that you buy at the station is primarily composed of hydrocarbons called octanes. The prefix oct- signifies the number “eight”, so these hydrocarbons contain eight carbon atoms.
Gasoline like any other molecule has potential energy, and this energy is stored in electrons in bonds.
So, in the case of octanes, the bonds between carbon atoms and the bonds between carbon and hydrogen atoms are stored, which will be later converted into kinetic energy to make your car GO.
In order for gasoline to do its job, it will travel from the fuel tank to the combustion chamber where it is injected and then mixed with air - oxygen.
This mixture of gasoline and oxygen is then ignited with a spark from the spark plug, which releases energy to move your car, and the by-products of carbon dioxide, CO2, and water, H2O, exit the car via the exhaust.
The reaction I just described is what chemists call a combustion reaction, which most people describe as “burning”.
So, when people say they “burned gas” in a casual conversation, there is certainly science behind those words, and the next time a mechanic tells you that you need a new spark plug or a fuel injector you now know their purpose and what you are paying for.
But, what if I told you that something similar to a combustion reaction occurs in your body to give you energy?
The chemical process that we use to get energy is called metabolism, and we obtain the energy we need, our fuel, by breaking down food molecules like carbohydrates.
Carbohydrates, like hydrocarbons, are carbon-based and when combined with oxygen, they also produce carbon dioxide and water – just like the combustion reaction we discussed earlier.
Is this just a coincidence?
The answer lies in the fact that atoms are atoms whether they are found in gasoline or inside your body, and by nature, atoms are constantly looking for ways to lower the energy of their electrons.
Atoms bond in order to lower their energy, which in turn makes them more stable. The stronger the bond, the lower is the energy of their electrons.
Something similar is happening in combustion reactions.
The reaction proceeds and produces carbon dioxide and water because in this process, weaker bonds are converted into stronger bonds.
The double bonds between the carbon and oxygen atoms of carbon dioxide are very strong, and the bonds between the oxygen and hydrogen of a water molecule are relatively strong as well.
Combined, these products are favorable from the atoms’ point of view because stronger bonds have been made which means that the overall energy of the electrons have been lowered.
And by having this discussion on the energy of the electrons, you’ve described the term enthalpy of a chemical reaction without realizing it.