According to the balanced chemical equation, the equivalence is: We are relating an amount of oxygen to an amount of carbon dioxide, so we need the equivalence between these two substances. If 154 mol of O 2 are reacted, how many moles of CO 2 are produced? Solution The example may seem simple because the numbers are small, but numbers won’t always be so simple!Ĭonsider the following balanced chemical equation:ĢC 4H 10(g) + 13O 2 → 8CO 2(g) + 10H 2O(ℓ) This is an example of a mole-mole calculation, when you start with moles of one substance and convert to moles of another substance by using the balanced chemical equation. Note how the mol H 2 unit cancels, and mol O 2 is the new unit introduced. If, for example, we want to know how many moles of oxygen will react with 17.6 mol of hydrogen, we construct a conversion factor between 2 mol of H 2 and 1 mol of O 2 and use it to convert from moles of one substance to moles of another: This chemical reaction gives us the following equivalences:Īny two of these quantities can be used to construct a conversion factor that lets us relate the number of moles of one substance to an equivalent number of moles of another substance. Consider the following chemical equation: However, now we understand that these equivalences are expressed in terms of moles. As such, chemical equations also give us equivalences-equivalences between the reactants and the products. In Chapter 4 “Chemical Reactions and Equations”, in the section called “The Chemical Equation”, we stated that a chemical equation is simply a recipe for a chemical reaction. One mole of elemental nitrogen reacts with three moles of elemental hydrogen to produce two moles of ammonia. We would speak of this equation as “one mole of molecular phosphorus reacts with five moles of elemental oxygen to make one mole of tetraphosphorus decoxide.” Test Yourself The coefficients represent the number of moles that react, not just molecules. Interpret this balanced chemical equation in terms of moles. We can just as easily read this chemical equation as “two moles of hydrogen react with one mole of oxygen to make two moles of water.” All balanced chemical reactions are balanced in terms of moles. This is the same balanced chemical equation we started with! What this means is that chemical equations are not just balanced in terms of molecules they are also balanced in terms of moles. Well, why not just use the number of moles in balancing the chemical equation? That means that the first and last numbers represent 2 mol, while the middle number is just 1 mol. But these numbers are related to the number of things in a mole: the first and last numbers are two times Avogadro’s number, while the second number is Avogadro’s number. These coefficients are also in the ratio of 2:1:2. So is this chemical equation:Īgain, this is not conventional, but it is still balanced. This equation is not conventional-because convention says that we use the lowest ratio of coefficients - but it is balanced. For instance, this chemical equation is also balanced: We interpret this as “two molecules of hydrogen react with one molecule of oxygen to make two molecules of water.” The chemical equation is balanced as long as the coefficients are in the ratio 2:1:2. Calculate moles of one substance from moles of another substance using a balanced chemical equation.Ĭonsider this balanced chemical equation:. Use the balanced equation to construct conversion factors in terms of moles.Balance a chemical equation in terms of moles.
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