Video Transcript
When lightning strikes, molecules of oxygen, O2, and nitrogen, N2, in the atmosphere are given enough energy to combine together to form nitric oxide, NO. Under normal conditions, oxygen and nitrogen molecules collide but do not react. What does this suggest about the reaction? (A) It cannot be performed without a catalyst. (B) It is reversible. (C) It is irreversible. (D) It is catalyzed by lightning. (E) It has a very large activation energy.
This problem tells us about the reaction where oxygen and nitrogen combine to form nitric oxide. When lightning strikes, the reaction occurs and nitric oxide is formed. But without the lightning, nothing happens. So what does this tell us about the reaction?
Answer choices (A) and (D) have to do with catalysts. A catalyst is some kind of chemical agent that increases the rate of a reaction. Answer choice (D) says that the reaction is catalyzed by lightning. Lightning is not a chemical agent, so it doesn’t fit the definition of a catalyst. So answer choice (D) isn’t correct. Answer choice (A) says that the reaction can’t be performed without a catalyst. Given that the reaction occurs when lightning strikes but lightning is not a catalyst, answer choice (A) doesn’t make much sense.
Answer choices (B) and (C) have to do with the reaction being reversible or irreversible. This reaction could be reversible. A reversible reaction is one that goes in the forward direction, where nitrogen and oxygen react to form nitric oxide, and it also goes in the reverse direction, where nitric oxide decomposes to form nitrogen and oxygen. Or the reaction might be irreversible, meaning it only goes in the forward direction. We don’t know. The problem doesn’t tell us this information. A lightning strike causing the reaction to occur doesn’t suggest that the reaction is reversible or irreversible.
This leaves us with answer choice (E), which has to do with the activation energy of the reaction. The activation energy is the minimum energy required for a reaction to occur. According to collision theory, particles must collide in order to react. In order for a reaction to occur, the particles must collide with the correct orientation and they must collide with enough energy. This energy is the activation energy. A lightning strike would provide a lot of energy to a reaction. After all, the temperature inside a lightning strike can be greater than 50,000 degrees Celsius.
So, in the reaction between oxygen and nitrogen, the lightning is providing the energy that’s needed for the reaction to occur. Since no reaction occurs when there’s no lightning, this must mean the reaction requires a lot of energy. This all suggests that answer choice (E) is the correct answer. The reaction has a very large activation energy.
