Stochiometrie is the branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. For many students, it is one of the most challenging topics in general chemistry. But once you understand the underlying logic, stoichiometry problems become almost mechanical — follow the steps, get the right answer.
The Stochiometrie Roadmap
Every stoichiometry problem follows the same basic path: convert what you know (usually grams) to moles, use the balanced equation to find the mole ratio, convert moles of the desired substance back to grams. That is it. Three steps. The tricky part is executing each step correctly and knowing when to add extra steps like identifying the limiting reactant or calculating percent yield.
Balancing Equations First
Before you can do any stoichiometry, you need a balanced chemical equation. Take the combustion of propane: C3H8 + O2 -> CO2 + H2O. Left unbalanced, the mole ratios are meaningless. The balanced version is C3H8 + 5O2 -> 3CO2 + 4H2O. This tells you that one mole of propane reacts with five moles of oxygen to produce three moles of carbon dioxide and four moles of water. Those coefficients are your roadmap for every subsequent calculation.
Our Molar Mass Calculator handles the grams-to-moles conversion, and the Mass-Mass Stochiometrie Calculator does the whole chain for you.
Limiting Reactant Problems
In real reactions, you rarely have exactly the right amounts of each reactant. Usually, one reactant runs out first — that is the limiting reactant. It determines how much product you can make. To find it, convert each reactant to moles, divide by its coefficient, and compare. The smallest result identifies the limiting reactant. The Limiting Reactant Calculator automates this process.
Percent Yield
Theoretical yield is the maximum amount of product you could get if everything went perfectly. Actual yield is what you actually obtain in the lab. Percent yield = (actual / theoretical) x 100%. A yield below 100% is normal and expected — some product is always lost during transfers, filtration, or side reactions. Yields above 100% usually mean the product is wet or contaminated. Use the Percent Yield Calculator to quickly determine your experimental efficiency.