How to Find the Limiting Reagent

---

The first step in finding the limiting reagent is to find the molar mass of each element given to you. 

• To find the molar mass look at the periodic table below and round the atomic number to the nearest whole value 

2nd step when finding the limiting reagent is to find the molesin the equation 

• To find the moles you can divide the grams given to you in the equation by the molar mass (which you found in step 1) 

Step 3 is to make a ratio that represents the two proportions given to you 

• First proportion: Look at the coefficients on the left side of the equation (if there are no numbers on the left of the equation the coefficient is automatically 1)
• Second proportion: For the second proportion, put the ratio you found in the first proportion = to the number of moles you found in step two (in ratio form) 

For step 4 you have your two proportions equal to each other and now you can cross multiply them Now that you have cross multiplied your two proportions you are left with two values. The last step is to determine which of the values is smaller and then connect that to its original element for the final answer. That smaller value is the limiting reagent


For the balanced equation shown below, what would be the limiting reagent if 56.8 grams of C2H2Cl2 were reacted with 34.9 grams of O2?

2C2H2Cl2+5O2=>4CO2+2H2O+2Cl2

C2H2Cl
or 
O2


Calculate the grams of O2 needed to react fully with 56.8 grams of C2H2Cl2, using the gram ratio provided by the balanced equation, as shown below.
From the balanced equation: (mass of O2)/(mass of C2H2Cl2)=160/193.88
(160/193.88)*56.8=46.9
Since the needed mass is more than than the mass given in the problem, the O2 is limiting and the C2H2Cl2 is excess .

---

What is the Limited Reagent: In chemistry, the limiting reagent, also known as the limiting reactant, is the chemical that determines how far the reaction will go before the chemical in question gets used up, causing the reaction to stop. The chemical of which there are fewer moles than the proportion requires is the limiting reagent. - Wikipedia

A couple real life examples of a limiting reagent are:

1) There are 4 ipods and 6 headphones, the limited reagents are the ipods

2) There are 2 computers plus 6 outlets, the limiting reagents are the computer plugs 

3) There are 10 avocado cucumber rolls and 14 pairs of chopsticks, the limited reagents are the sushi rolls 

take a quiz on finding the limiting reagent!