Chem 1ALecture 7HomeworkRead chapter 3ALEKS homework: XM4NG-QNDN6Chapter 3 book problemsConcise way to represent chemical reactions.2 H2(g) + O2(g)  2H2O(l)“+” = reacts with = produces Left of arrow = reactants Right of arrow = products Physical State(g) = gas(l) = liquid(s) = solid (aq) = aqueous Balancing Chemical Equations2 H2(g) + O2(g)  2H2O(l)In normal chemical reactions (non-nuclear) atoms are neither created nor destroyed. An equal number of atoms of each type are found on both sides of the equation. Stoichiometry – the quantitative relationship between products and reactants Balancing Chemical Equations• How many oxygen atoms are on each side of the equation?The left side of the equation has two oxygen atoms and the right side has three. Atoms cannot simply appear or disappear in chemical equations. We must account for the atoms on both sides of the equation. Balancing Chemical EquationsNotice also that the left side of the equation has four hydrogen atoms and the right side has only two.To correct these problems, we must create a balanced equation.Balancing Chemical Equations• To balance an equation, we insert coefficients—not subscripts—in front of the chemical formulas as needed to make the number of each type of atom in the reactants equal to the number of each type of atom in the products. • If there is no coefficient or subscript, a 1 is implied. The equation is now balanced because the numbers of each type of atom on both sides of the equation are equal. Balancing Chemical EquationsBalanced Equation for Chemical ReactionN2(g) + 3H2(g) → 2NH3 (g)reactants productsWhat does a balanced equation tell you?1) When one N2molecule reacts with three H2molecules then two NH3molecules are producedor2) When 1 mole N2reacts with 3 moles H2then 2 moles NH3 will be produced.Reading a Chemical EquationsAluminum metal reacts with oxygen gas to produce aluminum oxide. Write the balanced reaction.Al (s) + O2(g)  Al2O3(s)  Try ThisBalancing Chemical Equations4 Al (s) + 3 O2(g)  2 Al2O3(s)To Balance Rxn: Generally start with most complex molecule.Most reaction involve combining O2from air with a reactant.When hydrocarbons are combusted they form CO2+ H2O.Suppose we combust (or burn) methanol:CH3OH(l) + O2(g)  CO2(g) + H2O(l)1. Balance Carbons: CH3OH(l) + O2(g)  CO2(g) + H2O(l)2. Balance Hydrogens:CH3OH(l) + O2(g)  CO2(g) + 2H2O(l)3. Balance Oxygens:CH3OH(l) + 3/2 O2(g)  CO2(g) + 2H2O(l)4. Remove Fractional Coefficients2 CH3OH(l) + 3O2(g)  2 CO2(g) + 4 H2O(l)Combustion Reactions2 pieces bread + 1 piece ham  1 sandwichHave 14 pieces of bread, 8 pieces of ham How many sandwiches can you make?7What is the limiting item? breadWhat do you have left over? 1 piece of hamLimiting Reagent• The most expensive chemicals are chosen as the limiting reactants• Less expense reactants can be used in excess to ensure all of the expensive chemicals are completely used up (none wasted).Limiting Reactants in Industry4 Al (s) + 3 O2(g)  2 Al2O3(s)You have 1 mol Al and 1 mol O2Will the reaction occur to produce some Al2O3(s)?a) Yes b) NoLimiting Reagent4 Al (s) + 3 O2(g)  2 Al2O3(s)You have 1 mol Al and 1 mol O2Will the reaction occur to produce some Al2O3(s)?a) Yes b) NoLimiting Reagent4 Al (s) + 3 O2(g)  2 Al2O3(s)1 mol Al reacts with 1 mol O2Which is the limiting reagent?a) Al b) O2c) Al2O3d) not sureLimiting Reagent4 Al (s) + 3 O2(g)  2 Al2O3(s)1 mol Al reacts with 1 mol O2Which is the limiting reagent?a) Al b) O2c) Al2O3d) not sureLimiting Reagent4 Al (s) + 3 O2(g)  2 Al2O3(s)1 mol Al reacts with 1 mol O2How much O2left over?a) 1 mol b) 0.75 mol c) 0.25 mold) not sureLimiting Reagent4 Al (s) + 3 O2(g)  2 Al2O3(s)1 mol Al reacts with 1 mol O2How much O2left over?a) 1 mol b) 0.75 mol c) 0.25 mold) not sureLimiting Reagent2 pieces bread + 1 piece ham  1 sandwichHave 200 g bread, 200 g pieces of ham How many sandwiches can you make?What must you do first?Limiting ReagentN2 + 3H2  2NH3a) If if we combine 100 g of N2and 30 g of H2which is the limiting reagent?b) How much NH3is produced (in grams) assuming the reaction goes to completion? This is called the theoretical yield.Theoretical YieldN2 + 3H2  2NH3Do experiment: We combine 100 g of N2and 30 g of H2, and reaction produces 105.7 g of NH3.Calculate the percent yield.Percent YieldTo summarize:• Limiting reactant (or limiting reagent)—the reactant that is completely consumed in a chemical reaction• Theoretical yield—the amount of product that can be made in a chemical reaction based on the amount of limiting reactant• Actual yield—the amount of product actually produced by a chemical reaction.• Percent yield—(actual yield/theoretical yield)×100%Solution – is a homogeneous mixture of two or more substances.Solvent - is the component that is present in greater quantity.Solute - is the component that is present in lesser quantity. It is said to be dissolved in the solvent. Aqueous Solutions – Solutions where water is the solvent.A compound is soluble in a particular liquid if it dissolves in that liquid. A compound is insoluble if it does not dissolve in the liquid.When ionic compounds dissolve in water, they usually dissociate into their component ions. SolutionWaterHydrogen BondingNaCl vs. WaterWater is a polar solvent.NaCl(s)  Na+(aq) + Cl-(aq)MgCl2(s)  Mg2+(aq) + 2 Cl-(aq)MgSO4(s)  Mg2+(aq) + SO42-(aq)Ionic Compounds in WaterA. CaBr2B. NaNO3C. C6H12O6D. Two are strong electrolytesE. All of the aboveWhich of the following compounds is a strong electrolyte?A. CaBr2B. NaNO3C. C6H12O6D. Two are strong electrolytesE. All of the aboveWhich of the following compounds is a strong electrolyte?Electrolyte – a substance whose aqueous solutions contains ions and hence conduct electricity.Non electrolyte - a substance that does not form ions in solution. Aqueous SolutionsCH3CO2H (aq) ⇋ CH3CO2 -(aq) + H+(aq) Aqueous SolutionsStrong Electrolyte: Substance dissociates ~100%Producing lots of ions in solution.Weak Electrolyte: Substance dissociates a littleProducing a few ions in solutionNon Electrolyte: Substance may dissolveProduces no ions in solution