A given chemical reaction can be represented using a particulate diagram, in which the reaction mixture is depicted both before the reaction occurs and after the reaction has proceeded completely as possible. To be consistent with the law of conservation of mass, the "before reaction" and "after reaction" visualizations should each contain the same numbers and types of atoms. Created by Sal Khan.
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- why is there a leftover H20 when the methane and the water have the same proportions in the reactants side(2 votes)
- Why are 3 water molecules and 2 methane molecules drawn? Shouldn't it be just 1 molecule each?(2 votes)
- For a single reaction to take place, we would only require one molecule of water and methane each. If we have more molecules of water and methane, then that just means we have more than a single reaction take place. In this case, we have two reactions occur.
In a real reaction situation we have much more than one or two reactions taking place; more like billions upon billions. But no matter how many molecules of methane and water we have we know that they still react in a 1:1 ratio according to the chemical equation.
Hope that helps.(2 votes)
- why are carbon atoms bigger than oxygen?(2 votes)
- Oxygen has a greater effective nuclear charge so its electrons are pulled in closer to the nucleus than are the carbon’s electrons to its nucleus. If the electron cloud is smaller then the atom itself is also smaller.
Hope that helps.(1 vote)
- Can you please make me understand why are we having 2 methane molecules and 3 water molecules in the structure you drew, because on the formula we're having a ratio of 1:1(1 vote)
- It’s not really a structure, it’s called a particulate diagram. It’s a pictorial representation of a reaction mixture where we have smaller drawings of spheres representing molecules.
The chemical reaction tells us what ratio of reactants need to react with each other for a successful reaction (in this case 1:1 for methane and water), but our actual reaction vessel does not necessarily have that same amount of reactants. Having two methane molecules and three water molecules in a reaction which reacts 1:1 means that two water molecules will be able to react with two methane molecules and leave behind an unreacted water molecule.
Hope that helps.(1 vote)
- [Instructor] In a previous video, we used a particulate model like this to understand a reaction, not just to understand the reaction, but to balance the chemical reaction as well. And when I hand drew these particles, the atoms in this particulate model here, I tried to draw it pretty close to their actual relative sizes. Carbon atoms are a little bit bigger than oxygen atoms, and they're both a lot bigger than hydrogen atoms. What we're gonna do in this video is extend our understanding using a particulate model to start to visualize what actually might go on in a mixture of some of these reactant molecules. So what I have here on the left-hand side are the various molecules. I have two methane molecules here. I have three water molecules. And what I wanna do with you is draw what we would expect to see after the reaction. And I encourage you, like always, pause this video and see if you can have a go at that, maybe with a pencil and paper, at least just try to imagine it in your head, before I do this with you. All right, now, let's do this together. Now, we know that for every methane and every water, we're going to produce one carbon monoxide and three molecular hydrogens. And each of those molecules of hydrogen have two hydrogens in them. So let's just say that this one and this one react. They're going to produce one carbon monoxide. I'm gonna try to draw the relative sizes roughly, right? So one carbon monoxide. And then they're gonna produce six hydrogen atoms that are going to be in three hydrogen molecules. So let's do, that's two and four, and then I'll just do one here and then six. All right, so I took care of this one and this one. And now we can imagine that maybe this water molecule reacts with this methane molecule, and so that would produce another carbon monoxide. Let me draw that roughly at the right size. Another carbon monoxide molecule and three more hydrogen molecules for a total of six more hydrogens. So that's one and two and three. And now we have this water right over here that had no one to react with in this situation, had no partner. And so that's just going to be a leftover reactant molecule. So let me just draw it right over here. So that water could be right over right over here. And so this was a useful way of starting to visualize what might be going on. Remember, this is happening at a very high temperature. They're all bouncing around, et cetera. And then when they react, you might get this, but then this water molecule has no one to react to, so it is, you could view it as a leftover after the reaction.