Question

How would I go about figuring out a problem like this:

If 0.740 g of O3 reacts with 0.670 (g) of NO, how many grams of NO2 will be produced?

I'm absolutely stuck. Thanks!

Answer 1

As a first step, write out and then balance the chemical formula for the reaction. It's your guide for the rest of the problem. So in this case the unbalanced formula looks like:

O3 + NO --> NO2

How would you go about balancing it?

Answer 2

I have the equation as O3 (g) + NO (g) --> O2 (g) + NO2 (g)

Do I need to find the number or moles of the reactants? I vaguely remember my chem prof saying something along those lines...maybe?

Answer 3

Yup, that is exactly where we are going. But the first step is to get the formula right.

In this case the question gives NO2 as the only product, not O2 as well. So the product will only be in terms of NO2.

To balance the forumla, we need the same number of atoms going in on the reactant side and coming out on the product side. To get that, we multiply the NO by 3. The balanced formula looks like:

O3 + 3NO --> 3NO2.

Take a minute to count the atoms going into the reaction (6 oxygens, 3 nitrogens) and make sure they jive with the atoms going out (3 nitrogens and 3 x 2 = 6 oxygens)...

Answer 4

I initially thought the same thing about balancing it, but then I scrolled down on the problem I was given and what I listed above is the reaction equation that was given to us. Sorry for not realizing that before.

Answer 5

OK, cool. So if you ever get a problem which doesn't give you the formula, the first step is to write one out and balance it.

The next step is to interpret the formula which I restate here for my own reference:

O3 + NO --> O2 + NO2

The formula is basically a ratio. For the moment it doesn't matter whether you think about it in terms of single atoms, or moles, or teaspoons or whatever measurement you like. I use single atoms for ease. It says that one atom of O3 reacts with one atom of NO2 to form one atom of O2 and one atom of NO2. In this case the ratio is simply 1 to 1 to 1 to 1. That's not always the case, but it is for this problem.

Answer 6

Yes I am. The formula showing ratios make sense.

Answer 7

Step three is to figure out how many moles of the reactants we have. If we know how many moles go into a reaction, from the ratio above we can tell how many moles of product are formed.

To figure out how many moles of reactant there are, you have to do a little math. Specifically, you first have to figure out what the molecular weight is of each of the reactants and then from that you have to figure out how many moles of the reactants are present.

So for example, the molecular weight of O3 are 3 * 16 = 48 and the molecular weight of NO is 16 + 14 = 30. Those are both in grams.

Cool thus far?

Answer 8

Yes! So then you divide the number of grams by the molecular weight to get the number of moles. Right? So O3 would have 0.015 mol and NO would be 0.022 mol.

Answer 9

Yes, exactly.

Now the fourth step is to interpret that in terms of the chemical equation.

So we know that one mole of O3 reacts with one mole of NO. We have 0.015 moles of O3 and 0.022 moles of NO. The NO is present in excess of O3 - only 0.015 moles of NO can be used in the reaction because there are only 0.015 moles of the other reactant available for it to react with.

And similarly, only 0.015 moles of each of the products can be formed because only 0.015 moles of reactants can go into the reaction.

That is the key to the entire problem so take your time with it.

Answer 10

Aha! Ok, I think I get it now. So then you multiply the 0.015 by the molecular weight of NO2 in order to get the number of grams produced.

Answer 11

Yes, the last step from moles to grams of product is straight forward. So to recap the process:

1. Get the chemical formula.
2. Interpret the formula and figure out the ratios between all the compounds in the reaction. Those are just the coefficients on the compounds in the chemical formula.
3. Figure out how many moles of each reactant you have.
4. Figure out which reactants limit the reaction and which are present in excess. That will give you how many moles of product are formed.
5. Convert the moles of product into grams.

And you are home dry.

Answer 12

Oh excellent! Thank you so much for walking me through that. I appreciate it.

Answer 13

Not a prob, I'm glad you get it now! :D