What a Limiting Reagent Is and The Steps Towards Identifying It
To help answer this question i will use an ice cream cone as an example. Lets say that this ice cream cone can hold 2 scoops of ice cream, this means you need two ingredients, the ice cream (2 scoops)and the cone (1 cone). If you have 12 scoops of ice cream and 8 cones, the limiting reagent is the ingredient which makes it impossible to create any more ice cream cones, in this case the scoops of ice cream since you need 2 scoops per cone, and you only have enough for 6 cones. Heres an more complicated exampled in chemical form:
Bold = Important
For the balanced equation shown below, what would be the limiting reagent if 50.9 grams of C2H4F2 were reacted with 24.6 grams of O2?
2C2H4F2+3O2=>4CO+2H2O+4HF
O2 or C2H4F2
Step 1: Convert from grams to moles by using the formula Moles=Grams/Molar Mass
Step 1a: Find each chemical on the left hand side of the equations molar mass.
O2= (O= 16 --> O2= 16 X 2 = 32) 32 Molar Mass
C2H4F2= (C=12--> C2= 12 X 2= 24) +(H=1 --> H4= 1 X 4= 4)+(F=19-->F2=19 X 2= 38)= 24+4+38= 66 Molar Mass
Step 1b: Identify amount of grams in each chemical.
O2= 24.6 grams
C2H4F2=50.9 grams
Step 1c: Use formula to convert each chemical from grams to moles.
O2- Moles= 24.6/32=.76875 moles
C2H4F2- Moles= 50.9/66- .772 moles
Step 2: Compare their ratios. To do this you can see if the C2H4F2 is 2/3rds of the amount of O2. If it is more than 2/3rds, than the O2 is the limiting reagent. If it is less than 2/3rds the the C2H4F2 is the limiting reagent.
Ratio- 3O2 -- 2C2H4F2
Real Ratio- .76875 (O2) -- .772 (C2H4F2)
Step 3: Identify the limiting reagent.
The limiting reagent is the O2, because the C2H4F2 has a greater amount of moles than 2/3 of the O2 moles.
Important Rules
1. The unit in measuring chemicals are Moles. If it is not in moles, you must convert it to moles.
Use this formula to convert Grams to Moles
Moles= Grams/Molar Mass
2. The number located before the chemical on the left hand side of the equation is the amount in the ratio
example. 2C2H4F2+3O2=>4CO+2H2O+4HF
-- the ratio is 3 O2- 2C2H4F2 (for every 2 moles of C2H4F2 you need 3 moles of O2)
3. Always double check to make sure you have compared the ratios correctly, and converted to moles correctly.
