Calculating the theoretical yield is an important part of chemistry. It helps us figure out the most product we can make from the materials we start with. Here’s a simple guide to understand how to do this.

Step 1: Write the Balanced Equation

First, you need to write a balanced equation for the reaction.

Let’s take a look at the reaction between hydrogen gas and oxygen to make water:
2H₂ + O₂ → 2H₂O

Step 2: Find Moles of Reactants

Next, find out how many moles you have of each reactant.

You can use this formula:
moles = mass (g) / molar mass (g/mol)

For example, if you have 4 grams of H₂, and its molar mass is about 2 g/mol, then:
moles of H₂ = 4 g / 2 g/mol = 2 moles

Step 3: Use Stoichiometry

Now, use your balanced equation to find out which reactant is the limiting one.

The limiting reactant tells you how much product you can make.

Step 4: Calculate Theoretical Yield

Next, calculate the theoretical yield using the moles of the limiting reactant.

For every 2 moles of H₂, we get 2 moles of H₂O. If H₂ is the limiting reactant, you can produce 2 moles of water.

Step 5: Convert to Mass

Finally, you’ll want to change the moles of the product into grams.

Use this formula:
mass of H₂O = moles × molar mass = 2 moles × 18 g/mol = 36 g

This means the theoretical yield of water is 36 grams.

You can use this information to calculate the percent yield by comparing it to the actual amount of water you got in your experiment.