Unit 13: Stoichiometry -How can we quantitatively analyze reactions? -What limits the yield of a reaction? Why should we care? -How can a chemical equation best represent a reaction? -What are the patterns we can use to accurately predict products?

State Symbols In a chemical equation, we want to communicate as much information about our reaction as possible. We often use a set of symbols to note what state of matter the __________ and the ____________ are in. Consider the following reaction from our lab: reactants products

2 Mg + O2  2 MgO State Symbols In what state of matter were each of the products and reactants? Reactants Magnesium _________ Oxygen___________ Products Magnesium oxide __________ solid gas solid

State Symbols Mg + 2 HCl  MgCl2 + H2 To indicate each of the states of matter, we use a subscripted letter or two after each substance in the reaction. (s) – solid (g) – gas (l) – liquid (aq) – aqueous solution

State Symbols Mg + 2 HCl  MgCl2 + H2 Incorporating them in to our equation makes it look like this: Mg + 2 HCl  MgCl2 + H2 As you can see, the subcripted state symbols are written in the same position as the numerical subscripts for a compound But how do we know what states of matter to expect from our products or reactants outside of the lab? (aq) (g) (s) (aq)

States of Matter for Elements and Compounds In their elemental form, we know that most elements are solids at room temperature. What elements are exceptions to this? Liquids – _______________________ Gases – ________________________________ ________ For compounds, we will usually have them in one of two forms: solid or aqueous solution How do we know if a substance is soluble or not? Bromine and mercury Hydrogen, nitrogen, oxygen, fluorine, chlorine

Solubility Chart A very useful reference chart known as a solubility chart can tell you whether or not a substance is soluble in water. If it is soluble, we would use the______ symbol. If it is not, we would use the _____ to indicate that it had precipitated out of the solution. The following page shows a common solubility chart. (aq) (s)

S = soluble I = insoluble SS = slightly soluble X = other Bromide Br-   Bromide Br- Carbonate CO3-2 Chloride Cl- Hydroxide OH- Nitrate NO3- Oxide O-2 Phosphate PO4-3 Sulfate SO4-2 Aluminum Al+3 S X I Ammonium NH4+ Calcium Ca+2 SS Copper (II) Cu+2 Iron (II) Fe+2 Iron (III) Fe+3 Magnesium Mg+2 Potassium K+ Silver Ag+ Sodium Na+ Zinc Zn+2 S = soluble I = insoluble SS = slightly soluble X = other

Solubility Chart To determine whether or not a substance is soluble, you look at its cation and anion and see where they cross in the chart. Determine if the following are soluble: Sodium nitrate – ______________ Magnesium oxide – ______________ Copper (II) chloride – ______________ Copper (II) hydroxide – ______________ Zinc sulfate – ______________ soluble insoluble soluble insoluble soluble

Solubility Chart What would the chemical equation look like? What would happen if we put potassium chloride solution into a test tube with sodium nitrate? What would the chemical equation look like? KCl + NaNO3  KNO3 + NaCl With the state symbols, how would it appear? KCl(aq) + NaNO3(aq)  KNO3(aq) + NaCl(aq) All of our reactants and products are soluble, so what would we see? - NOTHING! We would say that there was “no visible reaction” which we abbreviate as NVR

Solubility Chart Write the chemical equation for the reaction of magnesium sulfate and potassium phosphate. Predict the products MgSO4 + K3PO4  Mg3(PO4)2 + K2SO4 Balance the chemical equation 3MgSO4 + 2K3PO4  Mg3(PO4)2 + 3K2SO4 Write in the state symbols using the solubility charts 3MgSO4(aq) + 2K3PO4(aq)  Mg3(PO4)2 (s) + 3K2SO4(aq)

Activity Series Single replacement reactions are different when it comes to predicting whether or not a reaction will occur. A metal will replace another metal in an ionic compound if the metal element is more “active” than the metal in the compound How do we know which metal is more active? Look at an Activity Series!

Lithium Potassium Calcium Sodium Magnesium Aluminum Manganese Zinc Metal Activity Series for Single Replacement Reactions Metal Metal Ion Reactivity Lithium Potassium Calcium Sodium Magnesium Aluminum Manganese Zinc Chromium Iron Lead Copper Mercury Silver Platinum Gold Li+ K+ Ca2+ Na+ Mg2+ Al3+ Mn2+ Zn2+ Cr2+, Cr3+ Fe2+, Fe3+ Pb2+ Cu2+ Hg2+ Ag+ Pt2+ Au+, Au3+ Most Reactive - Least Reactive

Activity Series The higher the metal is on the chart, the more active it is. It can replace any metal underneath it in an ionic compound when in solution Example: Al + CuCl2  Cu + AlCl3 This reaction was what you carried out at the end of the Chemical Changes lab, when the aluminum wire was placed into the solution of copper (II) chloride

Activity Series Determine whether the following reactions will occur or not, based on the activity series: Zinc and lead (II) nitrate _________ Calcium and copper (II) chloride __________ Iron and sodium hydroxide _________ Aluminum and zinc bromide _________ Aluminum and calcium carbonate ________ Aluminum and silver sulfide ________ Yes Yes No Yes No Yes

Activity Series The reaction occurs between the metal cations in solution gaining electrons from the metal atoms as they turn from atoms into ions Have the cations been reduced or oxidized? ________________________ How do you know? ________________________________________ ________________________________________ Reduced Gain electron – reduction , lose electron – oxidation

Quantitative Use of Equations Possible interpretations: Molecular ratios of reactants and products Mole ratios of reactants and products Mass ratios of reactants and products

Stoichiometry The study of the amount of reactants needed and products generated in a _________ _________. There are _________ steps needed to solve a Stoichiometry problem. If your initial units are __________ and your final units are moles, skip steps ___ and ___. You only need the mole-mole ratio from the coefficients of the chemical reaction. chemical reaction five moles 2 4

Stoichiometry Write a complete and _____________ chemical equation. Convert quantity of given into __________. Multiply by the mole _____ taken from the ________________ in the chemical equation. Convert from moles into the desired unit. _____________ units to ensure that correct conversion factors were used. balanced moles ratio coefficients Cancel out

Stoichiometry What volume of ammonia is produced if 25.0g of nitrogen (diatomic molecule) is reacted with excess hydrogen? Write a complete and _____________ chemical equation. _______________________________________ Convert mass of nitrogen into moles by dividing by the molar mass. balanced N2 + 3H2  2NH3 x 1mol N2 28 g N2 25.0 g N2

Stoichiometry Multiply by the mole ratio. ________________________________________ Convert moles into the desired units Cancel units. Answer: _______________ x 1mol N2 28 g N2 x 2 mol NH3 1 mol N2 25.0 g N2 x 1mol N2 28 g N2 x 2 mol NH3 1 mol N2 x 17.0 g NH3 1 mol NH3 25.0 g N2 x 1mol N2 28 g N2 x 2 mol NH3 1 mol N2 x 17.0 g NH3 1 mol NH3 25.0 g N2 30.4 g NH3

Limiting Reagents A limiting reagent is a reactant that is in less molar quantity or the reactant that determines the quantity of _________________. product produced

For example, if we react 2.5 grams of sodium with 300,000 grams of chlorine, we wouldn’t get 300,002.5 grams of sodium chloride We would run out of sodium atoms before we ran out of chlorine atoms Therefore, the sodium “limits” the amount of sodium chloride that can be produced and is our limiting reagent

Limiting Reagents Problem: How many grams of NH3 can be produced from the reaction of 20 g of N2 and 6 g of H2? Calculate the moles of each reactant. _______________________________________ 20 g N2 x 1 mol N2 28 g N2 = 0.713 mol N2 x 1 mol H2 2 g H2 6 g H2 = 3 mol H2

Limiting Reagents According to the equation, N2 + 3H2  2NH3 Problem: How many grams of NH3 can be produced from the reaction of 20 g of N2 and 6 g of H2? According to the equation, N2 + 3H2  2NH3 For every 1 mole of nitrogen, I would need ________ moles of hydrogen. However, I have been given 0.713 moles of N2 and 3 moles of H2. To use all the N2, I need 3 x 0.713 = 2.14 moles of H2. There would be __________________ moles H2 remaining. Therefore, nitrogen is the ___________ reagent and hydrogen is the __________ reagent. three 3 – 2.14 = 0.86 limiting excess

Limiting Reagents This means my Stoichiometry must be based on the quantity of nitrogen since I will need all of it producing the Ammonium. _______________________________________ 0.86 mol H2 x 2 g H2/1 mol H2 = 1.72 g H2 remains How much hydrogen was used? Answer: ______________________ x 1mol N2 28 g N2 x 2 mol NH3 1 mol N2 X 17.0 g NH3 1 mol NH3 20.0 g N2 = 24.28 g NH3 6 g H2 – 1.72 g H2 = 4.28 g H2

-How can we quantitatively analyze reactions? -What limits the yield of a reaction? Why should we care? -How can a chemical equation best represent a reaction? -What are the patterns we can use to accurately predict products?