# Relationship between mass of reactants and products in a chemical reaction

### BBC Bitesize - GCSE Combined Science - Avogadro constant and moles - OCR Gateway - Revision 3

The relationship between the products and reactants in a balanced chemical . Calculate the mass of reactants and products from a balanced chemical. Balanced chemical equations can be used to predict the relationship between the of the reactants consumed and the products formed in a chemical. How to use mole ratios from a balanced reaction to calculate amounts of reactants. Using a balanced chemical equation to calculate amounts of reactants and products is called . Example: Using mole ratios to calculate mass of a reactant glycolysis, the link reaction and the krebs cycle produce 10 NADH, 2 FADH2.

Given volume and molarity, it is possible to calculate mole or use moles and molarity to calculate volume.

## Avogadro constant and moles

This is useful in chemical equations and dilutions. Example 7 How much 5 M stock solution is needed to prepare mL of 2 M solution? These ratios of molarity, density, and mass percent are useful in complex examples ahead. Determining Empirical Formulas An empirical formula can be determined through chemical stoichiometry by determining which elements are present in the molecule and in what ratio.

The ratio of elements is determined by comparing the number of moles of each element present. Combustion of Organic Molecules 1.

What is the empirical formula of the organic molecule?

The problem requires that you know that organic molecules consist of some combination of carbon, hydrogen, and oxygen elements. With that in mind, write the chemical equation out, replacing unknown numbers with variables. Do not worry about coefficients here.

### Stoichiometry: stoichiometric ratio examples (article) | Khan Academy

This will give you the number of moles from both the unknown organic molecule and the O2 so you must subtract the moles of oxygen transferred from the O2. Moles of oxygen in CO2: With this we can use the difference of the final mass of products and initial mass of the unknown organic molecule to determine the mass of the O2 reactant. Determining Molecular Formulas To determine a molecular formula, first determine the empirical formula for the compound as shown in the section above and then determine the molecular mass experimentally.

But this isn't a math video, so I'll get the calculator out. That's 48 plusright, So one molecule of iron three oxide is going to be atomic mass units. So one mole or 6. So in our reaction we said we're starting off with 85 grams of iron oxide. How many moles is that? Well 85 grams of iron three oxide is equal to 85 over moles.

So that's equal to, 85 divided by equals 0. So everything we've done so far in this green and light blue, we figured out how many moles 85 grams of iron three oxide is.

And we figured out it's 0.

Because a full mole would have been grams. But we only have So it's point 0. And we know from this balanced equation, that for every mole of iron three oxide we have, we need to have two moles of aluminum. So if we have 0.

So we're going to need 1. I just took 0. Because the ratio is 1: For every molecule of this, we need two molecules of that. So for every mole of this, we need two moles of this.

**GCSE Science Chemistry (9-1) Reacting masses 1**

If we have 0. All right, so we just have to figure out how many grams is a mole of aluminum and then multiply that times 1. So aluminum, or aluminium as some of our friends across the pond might say. Aluminium, actually I enjoy that more.

Aluminium has the atomic weight or the weighted average is But let's just say that the aluminium that we're dealing with has a mass of 27 atomic mass units. So one aluminum is 27 atomic mass units. So one mole of aluminium is going to be 27 grams.

## Stoichiometry and Balancing Reactions

So if we need 1. And what is that? So we need And if we had more than Assign a stoichiometric coefficient of 1 to the most complex compound, NO. Now we can balance the remaining single-element compounds. In order to do this we will need to use fractional coefficients.

Typically a stoichiometric coefficient of "1" is not explicitly included when writing the chemical equation. We can get rid of the fractional coefficients by multiplying by 2 even though this is a perfectly acceptable balanced chemical equation.

Balanced, but without fractional coefficients At the very beginning of this problem, perhaps you could see this was the answer. If you can see the balanced equation by sight, you don't need to go by the guidelines. Remember they are only guidelines to help if you run into trouble. You can see by simply adding a 2 in front of NO, we violate the first guideline even though it leads us to a balanced equation. Balance the given chemical reaction.

This one may not be as easy to see the final answer so we will use the guidelines to balance the equation. N2O3 is the most complex species so we will add a 1 for its coefficient.

Now we can balance the remaining single element species.

### Chemical Reactions

In order to balance the number of atoms we need 2 atoms of N and 3 atoms of oxygen on the left side of the equation. Balanced The equation is now balanced. However, we can get rid of the fractional coefficient by again multiplying by 2. Balanced, without fractional coefficients Notice that in these two examples N2 and O2 react with a different stoichiometry to obtain different products. Is it necessary for the number of moles of the reactants to be equal to the number of moles of products?

Answer Not only does the stoichiometry tell us the mole relation between product and reactants but it will also tell us the mass relation.