Stoichiometry, Product Yield, and Limiting Reactants

In chemical reactions, atoms — which are the building blocks of reactants — are rearranged to form new entities called products. The law of the conservation of masses states that matter can neither be created nor destroyed. Thus, for a chemical reaction in an isolated system, the mass remains constant.

The number of atoms on the reactant side equals that on the product side, and we see that the equation is balanced. This relationship between reactant and product quantities is known as stoichiometry.

Now, let's practice balancing a chemical equation. Here are the coefficients for carbon dioxide and nitrogen dioxide to help you get started. First, let's count the number of atoms on each side. Pay attention to both the coefficient, which indicates how many molecules are in the equation, and the subscript, which tells us how many atoms are in a molecule.

Then, multiply the coefficient and subscript values for each atom. Repeat for all elements. If an element is in several molecules, simply add the number of atoms in each molecule. Once this is complete for all elements, check to see if the reaction is balanced.

At its current state, the equation is not balanced. We see that there is one nitrogen on the reactant side, but four on the product side. To balance nitrogen, we need four reactant molecules, so we multiply all its elements by four. This balances carbon as well. There are two hydrogen atoms on the product side. Thus, we will make 14 H2O products. This makes 38 oxygen atoms on the product side, which requires 19 oxygen molecules on the reactant side. Finally, the equation is balanced.

The relationship between coefficients represents the relationship between the molar amounts. In this equation, one molecule of methane reacts with two molecules of oxygen to make one molecule of carbon dioxide and two molecules of water. The reaction stops when any reactant is completely consumed, limiting the amount of product that can be made. That reactant is called the limiting reactant.

The maximum possible amount of product, which is called the theoretical yield, depends on the amount of the limiting reactant. However, the actual product yield may differ based on side reactions, loss from purification steps, or human error. The percent yield tells us what percentage of the theoretical yield was obtained and is determined with this equation.

In this lab, you will react nickel chloride hexahydrate with ethylenediamine to synthesize a nickel coordination complex. Then, you will measure the amount produced, determine the limiting reactant of the reaction, and calculate the percent yield of the product.