Video: Interpreting Fusion Diagrams

The diagram shows two nuclei fusing. Red circles represent protons and gray circles represent neutrons. How many protons are there in total before the reaction takes place? How many neutrons are there in total before the reaction takes place? How many protons are there in total after the reaction takes place? How many neutrons are there in total after the reaction takes place? Which element is the heaviest of the 2 nuclei before the reaction? How many helium nuclei does the reaction produce?

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Video Transcript

The diagram shows two nuclei fusing. Red circles represent protons and grey circles represent neutrons.

Okay, so as we’ve been told in the question, there are two nuclei — one and two — that are fusing; here is the reaction, after which two different nuclei — this one and this one — are formed as products.

Now, the first part of the question asks us, “How many protons are there in total before the reaction takes place?”

Now, as we’ve already said, before the reaction takes place, we’ve got this nucleus and this nucleus. So all we need to do is to count up the total number of red circles in these nuclei because red circles represent protons. And those are the two nuclei we had before the reaction.

So in total, before the reaction occurs, there are one, two, three protons in this nucleus and the other nucleus has one proton. So altogether, that makes four. And hence, we say that before the reaction takes place, there are four protons in total.

Now, the second part of the question asks us, “How many neutrons there are in total before the reaction takes place?”

So once again, in the same two nuclei, we count the total number of neutrons; that’s grey circles. So in this nucleus, there are one, two, three, four grey circles and in the second nucleus, there are none. Therefore, altogether, there are also four neutrons before the reaction takes place. And that is our answer to the second part of the question as well.

Moving on then, the next part of the question asks us, “How many protons are there in total after the reaction takes place?”

So now, we’re considering the two nuclei after the reaction. That’s this one and this one. How many protons are there in total in these two nuclei? So let’s start counting the red circles again. We’ve got one, two in the first nucleus and one, two in the second nucleus. This once again makes a total of four.

Therefore, we say that the total number of protons after the reaction is four; that’s the same as the total number of protons before the reaction.

Moving on then, we’ve been asked how many neutrons are there in total after the reaction takes place. So now, we’re counting the grey circles in the products of the reaction. So let’s start with this nucleus here: we’ve got one and two grey circles. And in the second nucleus, we’ve got another one and two. So yet again, that makes a total of four. That is, we have a total of four neutrons after the reaction takes place. Same as before the reaction took place, we also had four neutrons then.

Now, the fifth part of the question asks us, “Which element is the heaviest of the two nuclei before the reaction?” In other words, out of these two nuclei, which element is the heaviest one?

Now, what do we mean by heaviest? Well, we mean the nucleus with the largest number of nucleons; that’s protons and neutrons because that nucleus has the largest mass and can therefore be thought of as the heaviest. Now, in this case, before the reaction, the largest nucleus is this one here. So what element is this nucleus?

Well, we can recall that an element is defined by the number of protons in its nucleus. Now, this nucleus has one, two, three protons, three red circles. Therefore, we need to check our periodic table, which will tell us that the element with three protons is known as lithium. Therefore, our answer to this part of the question is that the element that is the heaviest of the two nuclei before the reaction is known as lithium.

And finally, we’ve been asked, “How many helium nuclei does the reaction produce?”

Now, these two nuclei are the products of the reaction. Each of these nuclei has two protons, two red circles. And if we consult our periodic table once again, then we can see that the element which has two protons in its nucleus is known as helium. Therefore, this nucleus is a helium nucleus because it has one, two protons. And the same is true for this nucleus; it’s also a helium nucleus.

And since both of these nuclei are products of the reaction, we can, therefore, say that there are one, two helium nuclei produced during the reaction. And this is our final answer to the last part of the question.

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