1. Copy down HW 2. Take out HW & COMPARE your work to your table partner’s

BELLWORK 1. Copy down HW2. Take out HW & COMPARE your work to your table partner’s S.Barry

Chemical Reactions & Equations S.Barry

Chemical Equations • Shows what takes place during a • chemical reaction • Reactant : (substances reacting) on left • Arrow - (→) at center ; yields or produces • Products: (new substances formed) on • right A + B  C + D PRODUCTS REACTANTS S.Barry

Coefficients: how many? ; # appears in FRONT of the formula • “molecules” for covalent substances • “moles“ of atoms • “units” for ionic substances 3CO2 2Mg  4MgO  3 molecules of carbon dioxide 2 moles of magnesium 4 units of magnesium oxide • Phases: • solid (s), liquid (l), gas (g), Aqueous (aq) S.Barry

Writing Equations CH4 + 2O2 CO2 +2H2O • Names of reactants: methane & oxygen • Names of products: carbon dioxide & water • How many of each (coefficient): __CH4 ____O2 ____CO2 ___H2O • Ratio of coefficients: ___: ____: ___: ___ S.Barry

Expressing Chemical Equations Word: carbon + oxygen yields carbon dioxide • Remember your diatomic gases: (BrINClHOF) Formula: C + O2→ CO2 Diagram: + → S.Barry

Expressing Equations with words Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) to produce • How many? • Of what? • In what state? One atom of solid zinc reacts with two molecules of aqueous hydrochloric acid one unit of aqueous zinc chloride and one molecule of hydrogen gas. S.Barry

Exothermic & Endothermic Processes – see RB pg 34 table 2.5 • Exothermic: release energy; surrounding temp increases • A + B → AB + energy • CH4 + 3 O2→ CO2 + 2 H2O + energy • Endothermic: require/absorb energy; surrounding temp decreases • AB + energy→ A + B • H2O(s) + energy → H2O (l) Endothermic video http://www.youtube.com/watch?v=5RJLvQXce4A S.Barry

Law of Conservation of Mass/Matter/Energy • Matter is neither created nor destroyed in chemical reactions. In any chemical total numbers & kinds of atoms must remain unchanged in the reaction. This is called a balanced equation. • Charge, energy, mass, and # atoms are conserved (unchanged) in balanced reactions 4 H 2 O 4 H 2 O 36 g 4 g 32 g S.Barry

Signs of a Chemical Reaction • Evolution of heat and light • Formation of a gas • Formation of a precipitate • Color change S.Barry

Chemical Change – chemical composition changes Physical Change – chemical composition remains the same Examples of a physical change • Ripping, tearing, breaking • Boiling, melting, freezing, vaporing a substance (a phase change) • dissolving Signs of a Chemical Reaction • Evolution of heat and light • Formation of a gas • Formation of a precipitate • Color change Examples of a chemical change • Burning, rusting, oxidizing • Flammable, explosive, reacting S.Barry

Chemical Reactions II. Balancing Equations S.Barry

A. Balancing Steps 1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients to make #s equal. Coefficient  subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!! S.Barry

B. Helpful Tips • Balance one element at a time. • Update ALL atom counts after adding a coefficient. • If an element appears more than once per side, balance it last. • Balance polyatomic ions as single units. • “1 SO4” instead of “1 S” and “4 O” S.Barry

C. Balancing Example Al + CuCl2 Cu + AlCl3 Al Cu Cl Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2 3 3 2  2  6 1 1 1 1 2 3 2  3  6   3 S.Barry

Chemical Reactions III. Types of Chemical Reactions S.Barry

A. Combustion • the burning of any substance in O2 to produce heat A + O2 B CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) S.Barry

A. Combustion • Products: • contain oxygen • hydrocarbons form CO2 + H2O Na(s)+ O2(g)  Na2O(s) 4 2 C3H8(g)+ O2(g)  CO2(g)+ H2O(g) 5 3 4 S.Barry

B. Synthesis • the combination of 2 or more substances to form a compound • only one product A + B  AB S.Barry

B. Synthesis H2(g) + Cl2(g)  2 HCl(g) S.Barry

B. Synthesis • Products: • ionic - cancel charges Al(s)+ Cl2(g)  AlCl3(s) 2 3 2 S.Barry

C. Decomposition • a compound breaks down into 2 or more simpler substances • only one reactant AB  A + B S.Barry

C. Decomposition 2 H2O(l)  2 H2(g) + O2(g) S.Barry

C. Decomposition • Products: • binary - break into elements KBr(l)  K(s) + Br2(l) 2 2 S.Barry

D. Single Replacement • one element replaces another in a compound • metal replaces metal (+) • nonmetal replaces nonmetal (-) A + BC  B + AC S.Barry

D. Single Replacement Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) S.Barry

D. Single Replacement • Products: • metal  metal (+) • nonmetal  nonmetal (-) • free element must be more active(check activity series-Table J) Fe(s)+ CuSO4(aq)  Cu(s)+ FeSO4(aq) Br2(l)+ NaCl(aq)  N.R. S.Barry

E. Double Replacement • ions in two compounds “change partners” • cation of one compound combines with anion of the other AB + CD  AD + CB S.Barry

E. Double Replacement Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq) S.Barry

E. Double Replacement • Products: • switch negative ions • one product must be insoluble(check solubility table) Pb(NO3)2(aq)+ KI(aq)  2 2 PbI2(s)+ KNO3(aq) NaNO3(aq)+ KI(aq)  N.R. S.Barry

1. Copy down HW 2. Take out HW & COMPARE your work to your table partner’s