Stoichiometric Calculations Stoichiometry

A. Proportional Relationships b I have 5 eggs. How many cookies can I make? 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips Makes 5 dozen cookies. 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 5 eggs5 doz. 2 eggs = 12.5 dozen cookies Ratio of eggs to cookies

A. Proportional Relationships b Stoichiometry relationships between substances in a chemical reaction based on the mole ratio b Mole Ratio indicated by coefficients in a balanced equation 2 Mg + O 2  2 MgO

What can we do with Stoichiometry? b For the generic equation: R A +R B → P 1 + P 2 Given the……one can find the… Amount of R A (or R B )Amount of R A (or R B ) that is needed to react with it Amount of R A or R B Amount of P 1 or P 2 that will be produced Amount of P 1 or P 2 you need to produce Amount of R A &/or R B you must use

Given the equation… 2TiO 2 + 4Cl 2 + 3C → 2TiCl 4 + CO 2 + 2CO b How many mol chlorine will react with 4.55 mol carbon? b Given: 4.55 mole C b Find: mole Cl 2 b 6.07 mol Cl 2 will react with 4.55 mol carbon

Given the same equation… 2TiO 2 + 4Cl 2 + 3C → 2TiCl 4 + CO 2 + 2CO b What mass titanium (IV) oxide will react with 4.55 mol carbon? b given = 4.55 mol C b find = mass of TiO 2 b g TiO 2 will react with 4.55 mol carbon

B. Stoichiometry Steps 1. Write a balanced equation. 2. Identify the given and find. 3. Line up conversion factors. Mole ratio - moles  moles Molar mass -moles  grams Molarity - moles  liters soln Molar volume -moles  liters gas Core step in all stoichiometry problems!! Mole ratio - moles  moles 4. Check answer.

1 mol of a gas=22.4 L at STP C. Molar Volume at STP S tandard T emperature & P ressure 0°C and 1 atm

C. Molar Volume at STP Molar Mass (g/mol) 6.02  particles/mol MASS IN GRAMS MOLES NUMBER OF PARTICLES LITERS OF SOLUTION Molar Volume (22.4 L/mol) LITERS OF GAS AT STP Molarity (mol/L)

D. Stoichiometry Problems b How many moles of KClO 3 must decompose in order to produce 9 moles of oxygen gas? 9 mol O 2 2 mol KClO 3 3 mol O 2 = 6 mol KClO 3 2KClO 3  2KCl + 3O 2 ? mol9 mol

b How many grams of KClO 3 are req’d to produce 9.00 L of O 2 at STP? 9.00 L O 2 1 mol O L O 2 = 32.8 g KClO 3 2 mol KClO 3 3 mol O g KClO 3 1 mol KClO 3 ? g9.00 L D. Stoichiometry Problems 2KClO 3  2KCl + 3O 2

D. Stoichiometry Problems b How many grams of silver will be formed from 12.0 g copper? 12.0 g Cu 1 mol Cu g Cu = 40.7 g Ag Cu + 2AgNO 3  2Ag + Cu(NO 3 ) 2 2 mol Ag 1 mol Cu g Ag 1 mol Ag 12.0 g? g

63.55 g Cu 1 mol Cu D. Stoichiometry Problems b How many grams of Cu are required to react with 1.5 L of 0.10M AgNO 3 ? 1.5 L.10 mol AgNO 3 1 L = 4.8 g Cu Cu + 2AgNO 3  2Ag + Cu(NO 3 ) 2 1 mol Cu 2 mol AgNO 3 ? g 1.5L 0.10M

The Limiting Reactant A balanced equation for making a Big Mac® might be: 3 B + 2 M + EE  B3M2EE With……and… …one can make… 30 M excess B and excess EE 15 B 3 M 2 EE 30 B excess M and excess EE 10 B 3 M 2 EE 30 M 30 B and excess EE 10 B 3 M 2 EE

A balanced equation for making a tricycle might be: 3 W + 2 P + S + H + F  W3P2SHF With……and… …one can make… 50 P excess of all other reactants 25 W 3 P 2 SHF 50 S excess of all other reactants 50 W 3 P 2 SHF 50 P 50 S and excess of all other reactants 25 W 3 P 2 SHF

Solid aluminum reacts w/chlorine gas to yield solid aluminum chloride. 2 Al(s) + 3 Cl2(g)  2 AlCl3(s) If 125 g aluminum react w/excess chlorine, how many g aluminum chloride are made? = 618 g AlCl 3

If 125 g chlorine react w/excess aluminum, how many g aluminum chloride are made? = 157 g AlCl 3 b If 125 g aluminum react w/125 g chlorine, how many g aluminum chloride are made? 157 g AlCl 3 b We’re out of Cl 2.

b limiting reactant (LR): the reactant that runs out first Amount of product is based on LR. b Any reactant you don’t run out of is an excess reactant (ER).

Example Limiting Reactant Excess Reactant(s) Big Macsbunsmeat tricyclespedalsW, S, H, F Al / Cl 2 / AlCl 3 Cl 2 Al

How to Find the Limiting Reactant b For the generic reaction R A + R B  P b Assume that the amounts of R A and R B are given. b Should you use R A or R B in your calculations?

How to find LR steps… 1. Calc. # of mol of R A and R B you have. 2. Divide by the respective coefficients in balanced equation. 3. Reactant having the smaller result is the LR.