Chemical equations describe CHEMICAL REACTIONS During a chemical

Chemical equations describe CHEMICAL REACTIONS. During a chemical reaction, the ways in which atoms are joined together are changed. OLD bonds are broken and NEW bonds are formed as REACTANTS are converted into PRODUCTS. A reaction STARTS with substances known as REACTANTS (always written on the LEFT side of the equation). The substances that are FORMED during a reaction are known as PRODUCTS (always written on the RIGHT side of the equation).

Chemical Equations are used (as chem. shorthand) to represent what is occurring during a chemical reaction. Ex. : Butane burns in oxygen to produce carbon dioxide gas and water vapor. C 4 H 10 + O 2 ---> CO 2 + H 2 O ∆

Why Balance Equations? When 9. 386 g Ca reacts completely with 7. 514 g S, 16. 90 g of Ca. S are formed. Ca(s) + S(s) ---> Ca. S(s)

Balancing Equations Make sure the chemical formulas are CORRECT (you cannot change the correct formula of a substance). I 2 Br 2 Cl 2 F 2 O 2 N 2 H 2 I Bring Clay For Our New House Use COEFFICIENTS (numbers in front of formulas) to change the number of atoms of an element. Coefficients represent MULTIPLES of the formulas

Balance the following N 2 (g) + (g) H 2 (g) ---> Fe. Cl 3 (s) ---> Fe(s) + NH 3 (g) Cl 2 Na. OCl + KI + HC 2 H 3 O 2 ---> I 2 + Na. Cl + KC 2 H 3 O 2 + H 2 O

Balance the following C 3 H 8 + O 2 --> CO 2 + H 2 O C 3 H 6 + O 2 --> CO 2 + H 2 O

Types of Chemical Reactions Combination Decomposition Single Replacement Double Replacement Neutralization Combustion A + B --> AB AB --> A + BC --> AC + BD --> AD + BC A + O 2 --> AO Cx. Hy + O 2 --> x CO 2 + y/2 H 2 O Red. Ox

Measuring MATTER Technique - Necessary information Counting - Avogadro’s # Weighing - Molar Mass Measuring Volume - Molar Volume

Types of Chemical Particles Atoms - represented by the symbol of an element (C, Ag, N, Na, Cl, Fe, Pb, S, etc. ) Molecules - represented by multiple symbol(s) of NONMETAL atoms/elements (CO 2, H 2 O, O 2, CH 4, etc. ) Ions - represented by the symbol/formula of an ion Formula Units - represented by the formula of an IONIC compound (Na. Cl, Ag. NO 3, Fe 2 O 3, etc. ) 1 mole = 6. 02 x 1023 particles (a conversion factor)

Avogadro’s Number = 6. 02 x 1023 This number can be determined experimentally several ways: Measurement of crystal structure Ti - body-centered unit cell (2 atoms/unit cell) # of atoms/mol = 6. 02 x 1023 atoms

MOLAR MASS The number of grams of a substance equivalent to the sum of all its average atomic mass units (amu) is known as the molar mass. One mole of particles is equal to its molar mass in grams.

MOLAR VOLUME The volume, 22. 4 L, of any gas at STP is known as the molar volume. STP = Standard Temperature and Pressure 273 K (O˚C, 32 ˚F) and 1 atm (101. 3 k. Pa, 760 mm Hg, 29. 92 in Hg)

Molar Conversions

STOICHIOMETRY -think recipes! Balanced chemical equations can be used to predict the QUANTITATIVE amounts of REACTANTS and PRODUCTS. N 2(g) + Particles Molecules Atoms Moles Mass 3 H 2 (g) ---> 2 NH 3 (g)

N 2(g) + 3 H 2 (g) ---> 2 NH 3 (g) How many moles of hydrogen will react with 0. 00326 mol N 2? How many molecules of ammonia are produced when 4. 55 x 1018 molecules of hydrogen react? How many atoms of hydrogen are in the ammonia produced? How many grams of nitrogen are required to react with 75. 8 g hydrogen?

Stoichiometry Use the stoichiometric mole ratio to convert from moles of one substance to moles of another substance within the reaction C 4 H 10 + O 2 ---> CO 2 + H 2 O How many moles of water are produced when 0. 48 moles of butane, C 4 H 10, react? How many molecules of butane are needed to produce 12. 00 grams of H 2 O?

Stoichiometry, cont. In the lab, we determine the masses of different substances, rather than moles, and therefore must be able to convert from grams of one substance in a reaction to grams of another. Na. OCl + KI + HC 2 H 3 O 2 ---> I 2 + Na. Cl + KC 2 H 3 O 2 + H 2 O How many grams of iodine are produced when 0. 35 g of potassium iodide react?

I 2 (aq) + Na 2 S 2 O 3(aq) --> Na 2 S 4 O 6(aq) + Na. I How many grams of sodium iodide are produced when 0. 203 g of iodine react with excess Na 2 S 2 O 3? Which reactant limits the amount of product that can be made? Why?

Limiting Reactants The product(s) of a reaction is/are limited by how much of each reactant is present (available) in the reaction. Two types of reactants Limiting - this is the reactant you run out of first! Excess - at the end of the reaction there will be some of this reactant left over (excess: -)).

Combustion of Magnesium Mg(s) + O 2(g in air) --> Mg. O(s) How much magnesium oxide can be produced when 1. 085 g Mg burns in air? Determine the limiting and excess reactants Calculate theoretical yield from the limiting reactant Mg(s) + O 2(g in air) --> Mg. O(s)

Molar Mass 208. 3 g/mol 76. 1 g/mol Ba. Cl 2 + NH 4 SCN --> Ba(SCN) 2 + NH 4 Cl 34. 5 g Ba. Cl 2 react with 44. 3 g NH 4 SCN. How much NH 4 Cl can be produced (theoretical yield)? STEP 1: Determine the LR and ER! (use mole ratio) STEP 2: Determine the Theoretical Yield from LR

Experimental Reaction Yield Balanced equations can be used to calculate the amount of product that will form during a reaction - called the THEORETICAL YIELD The amount of product that actually forms during a chemical reaction is called the ACTUAL YIELD The actual yield is often less than theoretical yield.

Percent Yield The percent yield is the ratio of the actual yield compared to theoretical yield, converted to a percent. actual yield % YIELD = ----------- x 100 theoretical yield

N 2(g) + H 2(g) ---> NH 3 (g) 0. 075 g N 2 react with 0. 0095 g H 2 to produce 0. 051 g NH 3. Which reactant is the limiting reactant? Which reactant is in excess? How much ammonia should be produced? What is the percent yield for this reaction?

Mole Ratios in Chemical Formulas The Empirical (Simplest) Formula is a ratio of atoms in the compound (this is equivalent to the mole ratio of atoms). Ex. If 3. 10 g Fe reacts with chlorine to make 9. 01 g of a compound, what is the simplest formula of the compound?

Mole Ratios in Chemical Formulas For hydrated compounds, the mole ratio of water to the compound is expressed in the formula. Ex. If 2. 00 g of a copper (II) sulfate hydrate is heated and the mass of the anhydrate is 1. 28 g, what is the formula of the hydrate?

Oxidation & Reduction Red. Ox Reactions that involve the transfer of electrons between “particles” are known as Red. Ox rxns. Oxidation is the loss of electron(s) from an atom. Reduction is the gain of electron(s) by an atom. OIL RIG Examples: Rusting; Batteries; Antiseptics; Combustion of Hydrocarbons; Reactions in Biochemical Pathways

Chemistry 104 Quiz #6 1. How many grams do 8. 5 x 1025 molecules of water weigh? 2. Balance the equation: C 6 H 14 + O 2 CO 2 + H 2 O 3. For the reaction: N 2 H 4 + 2 H 2 O 2 N 2 + 4 H 2 O How many grams of dinitrogen tetrahydride are needed to form 20. 0 g dihydrogen monoxide? 4. If 18. 0 g hydrogen peroxide react with the amount of dinitrogen tetrahydride determined in Q. #3 and produces 15. 6 g water, what is the percent yield?