Limiting Reactants Chapter 13

Plan of the day Intro to Limiting Reactants S’mores Example Problems Work through homework problems –Ch 13 HW Assignment: #1-9, 12,13 Chapter 13 Test: 5/4Chapter 13 Test: 5/4

Limiting Reactants—you will be able to…. (objectives) Define a limiting reactant Articulate the importance of a limiting reactant Identify the limiting reactant in a chemical reaction Calculate limiting reactant problems.

Definitions Reactant –Is a substance that takes part in a chemical reaction to make a product Limiting Reactant –The reactant that is completely used up in the reaction and limits the amount of product Excess Reactant –The reactant that is in excess, not all used up.

Why do we care? (Don’t write… just listen) Scientific Reasons –Determine how much reactant you need –Determine how much product will be produced Economic (Show me the money!) –Keep production cost’s minimal –Maximize output in production

S’mores Stoichiometry Limiting Reactants Complete S’mores wkst. #1-4 –We’ll get started together –When you are done, get a “S’mores Kit”

S’mores Kit Stoichiometry Record on back of your worksheet:Record on back of your worksheet: 1.Obtain a bag with s’more ingredients 2.Write the balanced equation for S’mores! 3.Using Stoichiometry, determine how many S’mores you can make with each ingredient given. 4.What is your limiting reactant? 5.Using stoichiometry, determine the amount of your excess reactants. 6.Wash your hands, and make yourself a S’more as a reward for a job well done 6.Wash your hands, and make yourself a S’more as a reward for a job well done

Steps in Solving LR problems! When two amounts of reactants are given in a problem, we need to identify the limiting reactant to solve for the amount of product possible! 1.Start with a Balanced Equation 2.Change grams of reactants to moles – this is how much you have. 3.Pick one of the reactants you just converted to mols (how much you have) & use Stoich from the balanced eqn to determine the number of mols of other reactant needed. 4.Compare mols of other reactant needed to what you have of that reactant… do you have enough? 5.Decide which is the limiting reactant

Another Method 1.Always begin with a BALANCED EQUATION!! 2.Convert the amount (grams/volume) of each reactant to moles of reactants. 3.Convert the number of moles of reactant to moles of product (doesn’t matter which one as long as you use the same product for both reactants) 4.Which ever reactant produces the least product is the limiting reactant.

Example 1 The reaction begins with 2.51g of HF and 4.56g of SiO 2.The reaction begins with 2.51g of HF and 4.56g of SiO 2. HF + SiO 2  SiF 4 + H 2 O Balance EquationBalance Equation Convert g  mols of each (What you have)Convert g  mols of each (What you have) Pick one & convert mols  mols of other reactant. This is what you need…Do you have enough?Pick one & convert mols  mols of other reactant. This is what you need…Do you have enough? If “yes,” then the other is your LR… if no than that one is your LRIf “yes,” then the other is your LR… if no than that one is your LR

How much excess reactant is left over? –Determine the amount of the excess reactant used then subtract from the starting amount.

How much product can be formed? Start with the amount (g) of limiting reactant, use stoichiometry (balanced equation) to find out the amount (g) of product!

Example 2 Determine the limiting reactant, if an 80.0g solution of NaOH, which is 40.0% NaOH by mass, reacts with a 75.0g solution of H 2 SO 4, which contains 45.0% water by mass. NaOH + H 2 SO 4  Na 2 SO 4 + H 2 O 1.Balance Equation 2.Calculate grams of NaOH and H 2 SO 4 3.g  mols of each (What you have) 4.Pick one & compare (What you need) 5.Do you have enough?

So… the reaction will go to completion until all the NaOH is used up. Calculate the amounts of each product that will be produced.

Reflection Looking at the objectives, give me a finger vote. 1—still feel clueless 5— makes perfect sense!

Example If 40.0 g of H 3 PO 4 react with 60.0 g of MgCO 3 calculate:If 40.0 g of H 3 PO 4 react with 60.0 g of MgCO 3 calculate: a.g of Mg 3 (PO 4 ) 2 produced b.g of CO 2 produced c.Volume of CO 2 at STP H 3 PO 4 + MgCO 3  Mg 3 (PO 4 ) 2 + CO 2 + H 2 O

IMPORTANT INFO… Chapter 13 HW:Chapter 13 HW: –#1-9, 12,13 Chapter 13 Test DatesChapter 13 Test Dates –5/4/15 (A-day)