Finding Limiting Reagents?

Question

If you have the equation of a reaction, and are told that there is 100grams of each of the reactant, what do you do in order to find which reactant will limit the production?

Answer 1

limiting agent problems are some of the longest in general high school chemistry  

do the stoichiometry for amount of reactants to products for each reactant to one of the particular products; whichever gives you the smallest amt of product is the limiting reactant

Answer 2

Let us do a problem so that you can follow the steps.

Problem: Sodium chloride is reacted with concentrated sulphuric acid the produce hydrochloric acid. If you have 100g of each (assume that the H2SO4 is 100%) which is the limiting reagent?

Step 1: Write a balanced equation:

2NaCl + H2SO4 → Na2SO4 + 2HCl

Step 2: Ignore the products - you are interested in the reactants only.

Step 3. Rewrite the balanced equation in moles of reactants

2moles of NaCl react with 1mole of H2SO4

Step 4. Convert this into grams

Molar mass NaCl = 23+35.5 =58.5 *2 = 117g

molar mass H2SO4 = 2+32+64 = 98g

Step 5: Now you can say:

117g NaCl reacts with 98g of H2SO4

Step 6: Divide the given mass of reactant by the reaction mass above

NaCl = 100/117 = 0.855

H2SO4= 100/98 = 1.020

Step 7: Because the NaCl has the smaller result, it is the limiting reactant.

As a further example, if you had been told that you were given 654g NaCl and 475g H2SO4, what would be the limiting reactant?

Go to Step 6:

NaCl = 654/117 = 5.59

H2SO4 = 475/98 = 4.85

In this case, the H2SO4 result is lower, so it is the limiting reactant.

If you follow this method, not difficult and not long to get the answer.