Chemical Reactions

 Chemical Reaction  Reactant  Product  Combustion Reaction  Decomposition Reaction  Single-replacement reaction  Double-replacement reaction  Precipitate  Solute  Solvent  Aqueous solution Using a textbook make a Vocab. Poster for 4 terms. Include: Name, Picture, and Definition

*Note Chapter 3 for review

Rusting Car

 4 indictors of a Chemical change…  Formation of a Precipitate  Formation of a gas  Color change  Temperature change (Absorption or release of heat)  Oder

Reactions and Equations

 have two parts: 1. Reactants = the substances you start with 2. Products = the substances you end up with  The reactants will turn into the products.  Reactants  Products  This is how you know a chemical reaction has occurred: Atoms of one or more substances are rearranged to form different substances  How to tell if a chemical reaction has taken place  Is there evidence? (Temperature change, color change, odor, gas bubbles, general appearance)

 Atoms aren’t created or destroyed  (Law of Conservation of Mass)  A reaction can be described several ways: #1. In a sentence every item is a word Copper solid reacts with chlorine gas to form copper (II) chloride solid. #2. In a word equation words and symbols are used to describe the reaction Copper (s) + chlorine (g)  copper (II) chloride (s) #3. In a skeleton equation uses symbols are used to describe the reaction Cu (s) + Cl 2(g)  CuCl (s) #4. In a chemical equation symbols are used to describe the reaction and is balanced 2Cu (s) + Cl 2(g)  2CuCl (s)

 the arrow ( → ) separates the reactants from the products (arrow points to products)  Read as: “reacts to form” or yields  The plus sign = “and”  (s) after the formula = solid: Fe (s)  (g) after the formula = gas: CO 2(g)  (l) after the formula = liquid: H 2 O (l)  (aq) after the formula = dissolves in water: NaCl (aq)

Fe +3 (s) + O 2(g)  Fe 2 O 3(s) Iron (III) reacts with diatomic oxygen to produce iron (III) oxide Cu +2 (s) + AgNO 3(aq)  Ag (s) + Cu(NO 3 ) 2(aq) Copper (II) reacts with silver nitrate to form silver and copper(II) nitrate.

 Atoms can’t be created or destroyed in an ordinary reaction:  All the atoms we start with we must end up with (meaning: balanced!)  A balanced equation has the same number of each element on both sides of the equation.

1)Assemble the correct formulas for all the reactants and products, using “+” and “ → ” 2)Count the number of atoms of each type appearing on both sides 3)Balance the elements one at a time by adding coefficients (the numbers in front) where you need more 4)Double-Check to make sure it is balanced.

 Never change a subscript to balance an equation (You can only change coefficients)  If you change the subscript (formula) you are describing a different chemical.  H 2 O is a different compound than H 2 O 2  Never put a coefficient in the middle of a formula; they must go only in the front 2 NaCl is okay, but Na 2 Cl is not.

 _AgNO 3 + _Cu  _Cu(NO 3 ) 2 + _Ag  _Mg + _N 2  _Mg 3 N 2  _P + _O 2  _P 4 O 10  _Na + _H 2 O  _H 2 + _NaOH  _CH 4 + _O 2  _CO 2 + _H 2 O

Classifying Chemical Reactions

 We will learn: the 5 major types.  We will be able to: predict the products.  How? We recognize them by their reactants

 Synthesize = put together  A + B  AB  2 substances combine to make one compound (also called “synthesis reaction”)  Ca + O 2  CaO  SO 3 + H 2 O  H 2 SO 4  We can predict the products, especially if the reactants are two elements.  Mg + N 2  Mg 3 N 2 (symbols, charges, cross)

 Additional Important Notes: 1. Two compounds can combine to form one compound. Calcium oxide and water form calcium hydroxide CaO (s) + H 2 O (l)  Ca(OH) 2(s) 2.A compound and an element can combine to form another compound sulfur dioxide gas reacts with oxygen gas to form sulfur trioxide 2SO 2(g) + O 2(g)  2SO 3(g)

 Combustion means “add oxygen”  a compound composed of only C, H is reacted with oxygen – usually called “burning”  incomplete, the products will be CO (or possibly just C) and H 2 O.  complete, the products will be CO 2 and H 2 O.

 Examples  C (s) + O 2(g)  CO 2(g)  These reactions are also synthesis reactions.  CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g)

 decompose = fall apart  AB  A + B  one reactant breaks apart into two or more elements or compounds.  2NaCl  2Na + Cl 2  CaCO 3  CaO + CO 2  Note that energy (heat, sunlight, electricity, etc.) is usually required electricity heat

 We can predict the products if it is a binary compound (which means it is made up of only two elements)  It breaks apart into the elements:  H 2 O  H + + OH -  NaNH 3(s)  Na (s) + NH 3(g)

 One element replaces another  A + BX  AX + B  Reactants must be an element and a compound.  Products will be a different element and a different compound.  Na + KCl  K + NaCl  F 2 + LiCl  LiF + Cl 2 (Cations switched) (Anions switched)

 Metals will replace other metals (and they can also replace hydrogen)  K + AlN   Zn + HCl   Think of water as: HOH  Metals replace the first H, and then combines with the hydroxide (OH).  Na + HOH 

 whether or not reaction will happen:  chemicals are more “active” than others  More active replaces less active

Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold 1)Metals can replace other metals, if they are above the metal they are trying to replace (for example, zinc will replace lead) 2)Metals above hydrogen can replace hydrogen in acids. 3)Metals from sodium upward can replace hydrogen in water. Higher activity Lower activity

Fluorine Chlorine Bromine Iodine Halogens can replace other halogens in compounds, provided they are above the halogen they are trying to replace. 2NaCl (s) + F 2(g)  2NaF (s) + Cl 2(g) MgCl 2(s) + Br 2(g)  ??? No Reaction! Higher Activity Lower Activity

 Two things replace each other.  Reactants must be two ionic compounds, in aqueous solution AX + BY  AY + BX  NaOH + FeCl 3   The positive ions change place.  NaOH + FeCl 3  Fe +3 +OH - + Na +1 + Cl -1 = NaOH + FeCl 3  Fe(OH) 3 + NaCl

 Have certain “driving forces”, or reasons  Will only happen if one of the products: a) doesn’t dissolve in water and forms a solid (a “precipitate”), b) is a gas that bubbles out, c) is a molecular compound (which will usually be water).

 Describes a reaction  Must be balanced in order to follow the Law of Conservation of Mass  Can only be balanced by changing the coefficients.  Has special symbols to indicate the physical state, if a catalyst or energy is required, etc.

 Come in 5 major types.  We can tell what type they are by looking at the reactants.  Single Replacement happens based on the Activity Series  Double Replacement happens if one product is: 1) a precipitate (an insoluble solid), 2) water (a molecular compound), or 3) a gas.

 Fill in the blanks on the table provided  Create a poster demonstrating each of the 5 reactions that we learned about

Writing Net Ionic Equations

 Many reactions occur in water- that is, in a aqueous solution  A solution contains one or more substances called solutes, what’s being dissolved in water. The water is called the solvent, what the substance is dissolved in.  When dissolved in water, many ionic compounds “dissociate”, or separate, into cations and anions.  Now we are ready to write an ionic equation

 Example (needs to be a double replacement reaction) AgNO 3(aq) + NaCl (aq)  AgCl (s) + NaNO 3(aq) 1. this is the full balanced equation 2. next, write it as an ionic equation by splitting the compounds into their ions: Ag 1+ + NO Na 1+ + Cl 1-  AgCl (s) + Na 1+ + NO 3 1- Note that the AgCl did not ionize, because it is a “precipitate,” it tells you that in the equation.

3. simplify by crossing out ions not directly involved (called spectator ions) Ag 1+ + Cl 1-  AgCl This is called the net ionic equation