Question: How can I solve a problem like this one: Identify the limiting reagent when 10.0 grams of hydrogen reacts with 60.0 grams of oxygen to form water.
Answer:
To solve limiting reagent problems, you need to first have a pretty complete knowledge of how to balance equations and do stoichiometry problems. Here's the basic thing you'll need to do to solve problems like this one:
1) Write a balanced equation for the reaction described in the problem. In this case, you'd write hydrogen (H2) and oxygen (O2) as the reagents and water (H2O) as the product. After balancing this equation, you end up with:
2) Determine how much of the product can be formed from each of the reagents, assuming that there was plenty of the other one. This requires two stoichiometry calculations: Find the amount of water that can be made from 10.0 grams of hydrogen, then find the amount of water that can be made from 60.0 grams of oxygen. When you do these calculations, you'll find that you can make 90.0 grams of water from 10.0 grams of hydrogen and 67.5 grams of water.
3) The limiting reagent is the reagent that was able to make the smallest quantity of product of the two reagents. In this case, since oxygen only made 67.5 grams of water and hydrogen made 90.0 grams of water, oxygen is the limiting reagent. This means that if you were to actually put ten grams of hydrogen together with sixty grams of oxygen and do this reaction, all of the oxygen would be consumed, some of the hydrogen would be left over (because there would be no oxygen for it to react with), and you'd make 67.5 grams of water.