Presentation on theme: "Limiting Reagents Limiting Reagent -- the reactant used up first in the chemical reaction. Excess Reagent(s) -- the reactant(s) present in quantities greater."— Presentation transcript:
1Limiting ReagentsLimiting Reagent -- the reactant used up first in the chemical reaction.Excess Reagent(s) -- the reactant(s) present in quantities greater than necessary to react with the quantity of the limiting reagent.
2Limiting ReagentThe concept of limiting reagent is analogous to the relationship between men and women in a dance at a club. If there are 14 men and only 9 women, then only 9 female/male pairs can compete. Five men will be left without partners. The number of women, thus limits the number of men that can dance in the contest, and there is an excess of men.
3Example # 1Consider the formation of nitrogen dioxide (NO2) from nitric oxide (NO) and oxygen (O2)2 NO(g) + O2(g) -----> 2 NO2(g)Suppose initially we have 8 moles of NO and 7 moles of O2.One way to determine the limiting reagent is to calculate the number of moles of NO2 obtained based on the initial quantities of NO and O2.Remember the limiting reagent will yield the smaller amount of the product.
4Calculate the number of moles of product obtained from each reactant Calculate the number of moles of product obtained from each reactant. The one that yields the smallest amount of product is the limiting reagent.
52 NO(g) + O2(g) -----> 2 NO2(g) Starting with 8 moles of NO, we find the number of moles of NO2 produced is8 mol NO x 2 mol NO2 = 8 mole NO22 mol NONow, starting with 7 moles of O2, the number of moles of NO2 produced is7 mol O2 x 2 mol NO2 = 14 mole NO21 mol O2
6Therefore, O2 is the excess reagent. Because NO yields the smaller amount of NO2, it must be the limiting reagent.Therefore, O2 is the excess reagent.
7Example # 2The depletion of ozone (O3) in the stratosphere has been a matter of great concern among scientists in recent years. It is believed that ozone can react with nitric oxide (NO) that is discharged from the high-altitude jet plane, the SST. The reaction isO3 + NO -----> O2 + NO2
8Example # 2 - continued If 0.710 g of O3 reacts with 0.670 g of NO, how many grams of NO2 will be produced?Which compound is the limiting reagent?Calculate the number of grams of the excess reagent remaining at the end of the reaction?
9This equation as it is written is balanced. Example # 2 - continuedFirst we need to make sure the equation is balanced:O3 + NO -----> O2 + NO2This equation as it is written is balanced.
10Example # 2 - continued = 1.027 g NO2 0.710 g O mole O3 1 mol NO g NO248.00 g O3 1 mol O mole NO2= g NO20.670 g NO 1 mole NO 1 mol NO g NO230.01 g NO 1 mol NO 1 mol NO2= g NO2
11Example # 2 - continuedb) Because O3 yields the smallest amount of NO2, it is the limiting reagent. Then, NO must be the excess reagent.c) 1O3 + 1NO -----> 1O2 +1NO2Because there is a 1 to 1 mole ratio between NO and NO2, then the amount of excess reagent left after the reaction is complete, assuming all of the O3 reacted, is:0.710 g O3 1 mol O mol NO g NO48.00 g O3 1 mol O mol NO= g NOTherefore, g NO – g NO = g NO remaining
12Practice Problem #1Propane (C3H8) is a component of natural gas and is used in domestic cooking and heating.(a) balance the following equation representing the combustion of propane in air:C3 H8 + O > CO2 + H2Ob) How many grams of CO2 can be produced by burning 3.65 moles of C3 H8? Assume that O2 is the excess reagent in this reaction.
13Practice Problem #2 2) Consider the reaction MnO2 + 4HCl ----> MnCl2 + Cl2 + 2H2OIf 0.86 mole of MnO2 and 48.2 g of HCl react,Which reagent will be used up first? Show your work.How many grams of Cl2 will be produced?
14Practice Problem #33) In the production of disulfur dichloride, molten sulfur reacts with chlorine gas according to the equation below:S8 (l) + 4 Cl2(g) ----> 4SCl2(l)If g of S react with 100.0g of Cl2,what mass of disulfur dichloride is produced?What reactant is the limiting reagent? Show your work.What reactant is the excess reagent? Show your work.How much of the excess reagent is left in grams?
15Practice Problem #44)The reaction between solid white phosphorus and oxygen produces solid tetraphosphorus decoxide (P4O10).Write the equation and balance it. Hint use the info. below to determine the reagents.Determine the mass of P4O10 formed if 25.0g of P4 and 50.0g of O2 are combined.What is the limiting reagent? Show your work.How much of the excess reactant remains after the reaction stops?
16Practice Problem #55) The reaction between solid sodium and iron(III)oxide is one is a series of reactions that inflates an automobile airbag.6Na(s) + Fe2O3(s) -----> 3Na2O(s) + 2 Fe(s)If g Na and g Fe2O3 are used in this reaction, determineThe limiting reagent.The reactant in excess.The mass of solid iron produced.The mass of excess reactant that remains after the reaction is complete.
17Practice Problem #66) Photosynthesis reactions in green plants use carbon dioxide and water to produce glucose (C6H12O6) and oxygen.Write the balanced equation.If a plant had 88.0g of carbon dioxide and 64.0 g water available for photosynthesis, determineThe limiting reactantThe excess reactant and the mass in excessThe mass of glucose produced