chemical reaction chemical equation. The chemical transformation of one substance to another is called a chemical reaction and is written using chemical formulas in what we call a chemical equation. 1 Chemical reactions Al + Br 2  AlBr 3 Chemical equation: reactantsproduct Chemical reaction: Aluminum reacts with bromine to produce aluminum bromide.

5. Change in pH (blue  red) (red  blue) 2 Chemical reactions can be observed and /or sensed:

Chemical Equations are Balanced To balance an equation, numbers called coefficients are used in front of formulas. 3

4 Na 3 PO 4 (aq) + MgCl 2 (aq) NaCl(aq) + Mg 3 (PO 4 ) 2 (s) Balance Polyatomic Ions as a unit PO 4 2 PO 4 2 2Na 3 PO 4 (aq) + MgCl 2 (aq) NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 6 NaNa 26 2Na 3 PO 4 (aq) + MgCl 2 (aq) 6NaCl(aq) + Mg 3 (PO 4 ) 2 (s) Mg3Mg 236 2Na 3 PO 4 (aq) + 3MgCl 2 (aq) 6NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 6 Cl

5 compositiondecomposition Double replacement Single replacement e + e  cmpd Al + Cl 2  AlCl 3 e + e  cmpd Al + Cl 2  AlCl 3 cmpd  e + e H 2 O  H 2 + O 2 cmpd  e + e H 2 O  H 2 + O 2 e + cmpd  cmpd + e Zn + HCL  ZnCl 2 + H 2 e + cmpd  cmpd + e Zn + HCL  ZnCl 2 + H 2 cmpd + cmpd  cmpd + cmpd HCl + NaOH  NaCl + H 2 O cmpd + cmpd  cmpd + cmpd HCl + NaOH  NaCl + H 2 O cmpd  cmpd + e KClO 3  KCl + O 2 cmpd  cmpd + e KClO 3  KCl + O 2 cmpd  cmpd + cmpd CaCO 3  CaO + CO 2 cmpd  cmpd + cmpd CaCO 3  CaO + CO 2 Types of reactions

6 combination reaction In a combination reaction, two or more elements (or simple compounds) combine to form one product 2Mg(s) + O 2 (g) 2MgO(s) 2Na(s) + Cl 2 (g)2NaCl(s) SO 3 (g) + H 2 O(l)H 2 SO 4 (aq) ABAB + decomposition reaction In a decomposition reaction, one substance splits into two or more simpler substances. 2HgO(s)2Hg(l) + O 2 (g) 2KClO 3 (s)2KCl(s) + 3O 2 (g) Potassium + oxygen? (names & formulas & balance) Water ? Formula(s), name(s) & balanced equation

7 single replacement In a single replacement reaction, one element takes the place of a different element in a reacting compound. Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) Fe(s) + CuSO 4 (aq) FeSO 4 (aq) + Cu(s) Mg(s) + H 2 O (l)  ? Formulas, names, & balance double replacement In a double replacement, two elements in the reactants exchange places AgNO 3 (aq) + NaCl(aq)AgCl(s) + NaNO 3 (aq) ZnS (s) + 2 HCl(aq)ZnCl 2 (aq) + H 2 S(g) Sodium hydroxide + HCl  ? Formula(s), name(s) & balanced equation

8 Oxidation-reduction reactions An oxidation–reduction reaction transfers electrons from one reactant to another (OIL) Reduction: gain e - (RIG) reduction oxidation Charge increases Charge decreases

Zn (s) + CuSO 4 (aq)  Cu (s) + ZnSO 4 (aq) oxidation Zn (s) Zn 2+ (aq) + 2e- reduction Cu 2+ (aq) + 2e- Cu(s) 9 Charges: Zn (s) + Cu SO 4 (aq)  Cu (s) + Zn SO 4 (aq) Sulfate does not change, therefore to simplify: Who is going up ? Znoxidation or reduction? oxidation Who is going down ?Cu oxidation or reduction? reduction Example

10 A reduces B Reducing agent A is the Reducing agent B oxidizes A Oxidizing agent B is the Oxidizing agent What is A doing to B? What is B doing to A? Mg + HCl  MgCl 2 + H 2 Reducing agentMg or HCl Oxidizing agentMg or HCl Mg itself is oxidized H in HCl itself is reduced

11 The Mole When particles get very small, counting them is more difficult and requires that we bundle them. Such is the case with eggs. The bundle has 12 eggs and it is called a dozen For very very small particles, such as atoms and molecules, the bundle gets larger. 12 = dozen mol Abbreviated mol whether singular or plural. The number 6.02 x is called Avogadro’s number the amount A mole is the amount of substance containing 6.02 x particles mole The Latin word for “bundle”, “heap”, “pile” is mole. mole The bundle has 6.02 x particles and it is called a mole.

12 elementatoms If the substance is an element the particles are atoms 1 mole of Na = 6.02 x Na atoms covalent compound molecules If the substance is an covalent compound the particles are molecules 1 mole of H 2 O = 6.02 x H 2 O molecules ionic compound formula units If the substance is an ionic compound the particles are formula units 1 mole of NaCl = 6.02 x NaCl formula units Equality:1 mole = 6.02 x particles Conversion Factors:6.02 x particles and 1 mole 1 mole6.02 x particles Avogadro’s number is used as a conversion factor: How many moles of CO 2 are in 2.50 x molecules of CO 2 ? 2.50 x molecules CO 2 x 1 mole CO 2 = 4.15 moles of CO x molecules CO 2

13 Molar Mass It is easier to weight particles than to count them. Therefore, we need a conversion factor between moles and grams. Molar Mass = the mass of one mole of a substance grams moles particles Avogadro’s Counting of particles is not practical ? ? grams 1 mole = the atomic mass of an element expressed in grams C12.0 g mole = the sum of the molar masses of the elements in the formula. H 2 O = g mole 6 C C We use molar masses to the nearest 0.1 g

Example: Aluminum is often used for the structure of lightweight bicycle frames. How many grams of Al in 3.00 moles of Al? 3.00 moles Al x 27.0 g Al = 81.0 g of Al 1 mole Al 14 Molar Mass is used as a conversion factor: 1 mole of CH 4 = 16.0 g of CH g CH 4 and 1 mole CH 4 1 mole CH g CH 4 Summary Molar Mass grams moles particles Avogadro’s countingby weighing The mole is a scientific concept that allows for the counting of atoms by weighing them. A mole is equal to the number of atoms in exactly 12 grams of pure C g C = 1 mol C atoms = 6.02 x C atoms

Relating coefficients to moles H N 2 2 NH 3 3 (molecules of H 2 )1 (molecule of N 2 )2 (molecules of NH 3 ) Impossible to work with such small quantities. 15 Mole Relationships in Chemical Equations :. Use a larger quantity, such as Avogadro's number 3(6.02 x molecules)1(6.02 x molecules)2(6.02 x molecules) Since 6.02 x = 1 mole moles 1 mole 2 moles Therefore: coefficients = moles

The coefficients can be placed in the form of mole ratios, which serve as conversion factors. the mole ratio of H 2 to N 2 is 3:1 3 mol H 2 1 mol N 2 the mole ratio of H 2 to NH 3 is 3:2 3 mol H 2 2 mol NH 3 16 Example: How many moles of NH 3 can be produced from 6.0 moles H 2 ? 6.0 mole H 2 x 2 mole NH 3 = 4.0 moles NH 3 3 mole H 2

The “map” A pictorial view of the steps and conversion factors needed to find the answer. moles grams MM Mole Ratio 17 Mass Calculations for Reactions N 2 (g) + 3H 2 (g) 2NH 3 (g)

= 85.0 g NH 3 Example: Suppose we want to determine the mass (g) of NH 3 that can form from 2.50 moles N 2. N 2 (g) + 3H 2 (g) 2NH 3 (g) moles grams ? mole N 2 given x 2 moles NH 3 1 mole N 2 mole ratio x 17.0 g NH 3 1 mole NH 3 molar mass