Limiting Reactant - The reactant in a chemical reaction ...



NOTES: STOICHIOMETRY PART 2: LIMITING REAGENTS

• Limiting Reactant - The reactant in a chemical reaction that limits the amount of product that can be formed.  The reaction will stop when all of the limiting reactant is consumed.

• Excess Reactant - The reactant in a chemical reaction that remains when a reaction stops when the limiting reactant is completely consumed.  The excess reactant remains because there is nothing with which it can react.

[pic]

In the example above, which is the limiting reagent?

In the example above, which is the excess reagent?

No matter how many tires there are, if there are only 8 car bodies, then only 8 cars can be made.  Likewise with chemistry, if there is only a certain amount of one reactant available for a reaction, the reaction must stop when that reactant is consumed whether or not the other reactant has been used up.

Example Limiting Reactant Calculation:

1. A 2.00 g sample of ammonia is mixed with 4.00 g of oxygen.  Which is the limiting reactant and how much excess reactant remains after the reaction has stopped?

• First, we need to create a balanced equation for the reaction:

4 NH3(g) + 5 O2(g)[pic]4 NO(g) + 6 H2O(g)

• Next we can use stoichiometry to calculate how much product is produced by each reactant.  NOTE:  It doesn’t matter which product is chosen, but the same product must be used for both reactants so that the amounts can be compared.

[pic]

• The reactant that produces the lesser amount of product in this case is the oxygen, which is thus the "limiting reactant."

• NEXT, to find the amount of excess reactant, we must calculate how much of the non-limiting reactant (ammonia) actually did react with the limiting reactant (oxygen).

[pic]

• We're not finished yet though.  1.70 g is the amount of ammonia that reacted, not what is left over.  To find the amount of excess reactant remaining, subtract the amount that reacted from the amount in the original sample.

[pic]

Limiting Reagent Sample Problem

When copper (II) chloride reacts with sodium nitrate, copper (II) nitrate and sodium chloride are formed.

1) Write the balanced equation for the reaction given above:

2) If 15 grams of copper (II) chloride react with 20 grams of sodium nitrate, how many grams of sodium chloride can be formed?

3) What is the limiting reagent for the reaction in #2?

4) What is the excess reagent for the reaction in #2?

5) How much of the excess reagent is left over in this reaction?

Limiting Reagent Key

All of the questions on this worksheet involve the following reaction: When copper (II) chloride reacts with sodium nitrate, copper (II) nitrate and sodium chloride are formed.

1) Write the balanced equation for the reaction given above:

CuCl2 + 2 NaNO3 ( Cu(NO3)2 + 2 NaCl

2) If 15 grams of copper (II) chloride react with 20 grams of sodium nitrate, how much sodium chloride can be formed?

To solve this problem determine how much sodium chloride can be made from each of the reagents by themselves. When you work out how much sodium chloride can be made with 15 grams of copper (II) chloride, you find that 13.0 grams will be formed. When starting with 20 grams of sodium nitrate, 13.6 grams will be formed. Since 13.0 grams is the smaller number, that’s our answer. Please note that rounding differences may cause your answers to be slightly different, so if they are, don’t panic.

3) What is the limiting reagent for the reaction in #2? copper (II) chloride

4) How much of the nonlimiting reagent is left over in this reaction?

Nonlimiting reagent remaining = 20 grams – 20 grams (13.0 / 13.6)

= 0.88 grams

-----------------------

Answer:

Answer:

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download