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If you're seeing this message, it means we're having trouble loading external resources on our website. To log in and use all the features of Khan Academy, please enable JavaScript in your browser. Science Chemistry Chemical reactions and stoichiometry Balancing chemical equations. Balancing Chemical Equations Intuition. Balancing more complex chemical equations.

Visually understanding balancing chemical equations. Balancing another combustion reaction.

The SQA Higher Chemistry data...

Balancing chemical equation with substitution. Balancing chemical equations 1. Video transcript - [Voiceover] We've now seen a couple of examples of balancing chemical equations.

Thus the half-life of a...

And we've seen that, okay, if let's say, we're trying to balance "How to start dating reactant" equation right over here and we started with the carbons. I have two carbons on the reactant side. They're both sitting in this ethylene molecule.

And so I would want two carbons on the product side. And right now, I only have one carbon on the product side. And so what we've done is let's just put a two out front here and so now we have two for every molecule of ethylene and we're not done balancing this chemical equation yet.

We're now producing two molecules of carbon dioxide. But one thing that you might have been thinking, "Why put this big two out front "of the entire carbon dioxide, "I like the way these little subscript little twos look, "so why not How to start dating reactant a two right over there.

It's no longer carbon dioxide, it's now this bizarre thing that doesn't really exist in nature. Which is a C2O2 thing.

Thus the half-life of a...

You're actually changing the reaction when you're doing that. When you're balancing chemical reactions, the reaction itself is, even before it's balanced is describing something that happens. When it's unbalanced, it How to start dating reactant doesn't have the numbers right in terms of number of molecules.

So the only thing that you can change when you're changing these is the number of molecules. You can't change the number of constituents within the molecule. And that's why we do not change these subscripts.

And if you want to visualize it a little bit differently, let's draw each of these molecules So ethylene How to start dating reactant like this. Then each carbon is bonded to two hydrogens. Notice you have two carbons and four hydrogens. It's oxygen doubled bonded to oxygen. And then you have carbon dioxide. Carbon dioxide is a carbon, double bonded, to two oxygens each.

And then finally, you have water. Finally, water, actually I'm going to do this in a slightly different color. Your water right over here, this is an oxygen bonded to two hydrogens. So let me write the plus signs there. So plus is right over there. So if you were to somehow write a subscript of two right over there, you would somehow be changing the structure, you would be changing what this molecule is.

Making and breaking bonds. To...

As opposed to that, which we don't want to do, we want to say, we're definitely producing carbon dioxide. We're definitely producing carbon dioxide, but how many carbon dioxides do we produce for each molecule of ethylene?

And so that's where we say, "Okay, we have two carbons here, "we want two carbons here.

So we're going to have two of these. Or if you want to do it, if you want to have it more visual, you could write it, okay, we're just going to have another molecule here. We're just going to have another molecule. So now we've balanced the carbons, two carbons on the reactant side.

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