Unit 07 Notes (Ch.8 in textbook) Chemical Reactions

Additional vocabulary:Additional vocabulary:  Acid-Base Reactions - Also called a neutralization reaction; occurs when an acid reacts with a base. They are considered one type of double-replacement reaction. Products will be a salt and H 2 O.  Precipitation Reactions – Occurs when two soluble ionic compounds react to form an insoluble product, the precipitate. Precipitates form when the electrostatic force of attraction between the ions is greater than the tendency of the ions to stay in solution. They are common in both nature and industrial processes. A type of double-replacement reaction.  Phlogiston - A hypothetical substance formerly thought to be a volatile constituent of all combustible substances, released as flame in combustion.

Father of Mother of Modern Chemistry Both lived during 18 th century  Antoine Lavoisier – father of modern chemistry  Lots of research on combustion  Disproved the theory of phlogiston  Marie-Ann Lavoisier – mother of modern chemistry  Lab assistant to her husband  Collaborator with her husband

 A substance that undergoes a reaction is called a __________.  Reactants are written on the left of the arrow  These will be the things you start with  When reactants undergo a chemical change, each  new substance formed is called a ___________.  Products are written on the right of the arrow  These are the things that you produce

Chemical EquationsChemical Equations chemical equations—use chemical formulas and an arrow to separate reactants from products Fe + O 2 → Fe 2 O 3 skeleton equation—shows just the formulas; does not show the relative amounts of reactants and products used in the reaction

States of Matter and SymbolsStates of Matter and Symbols  Use symbol to show the state of matter  (s) __________  (l) __________  (g) __________  (aq) __________ (substance dissolved in water) Fe (s) + O 2 (g) → Fe 2 O 3 (s)

Use of catalystsUse of catalysts  many times, a catalyst is employed in a reaction  catalyst—speeds up the rate of reaction but is not used up in the reaction (is written above the arrow in equation) MnO 2 2 H 2 O 2(aq)  2 H 2 O (l) + O 2(g)

Diatomic moleculesDiatomic molecules  Seven elements normally exist as diatomic molecules— these will always be written as X 2 when writing equations  H 2  O 2  N 2  F 2  Cl 2  Br 2  I 2  In order to write equations you MUST remember your diatomic elements…

 In a chemical equation the Law of conservation of matter MUST be observed!  This means the # of atoms of reactants = the # of atoms of products  What you start with has to equal what you end with

Balancing Chemical EquationsBalancing Chemical Equations  unbalanced equation—an equation that does not indicate the quantity of the reactants needed to make the products  balanced equation—gives the correct quantity of each reactant and product—each side of the equation has the same number of atoms of each element  coefficient—numbers placed in front of the symbols

1. Write the symbols for the reaction 2. Count the number of atoms of each element of the reactants. 3. Count the number of atoms of each element of the products. 4. Add / Change the coefficient to make the numbers of each element equal. 5. YOU CAN NEVER CHANGE A SUBSCRIPT ! 6. Write the coefficients in the lowest possible ratio. 7. Check your work. Steps for Balancing Chemical EquationsSteps for Balancing Chemical Equations

Types of ReactionsTypes of Reactions  There are 5 major classifications of reactions:  Synthesis (or Combination) A + B  AB  Decomposition AB  A + B  Combustion A + O 2(g)  AO 2  Single Replacement A + BC  AC + B  Double Replacement AB + CD  AD + CB Flash cards: Using the piece of paper given to you, write the name of each reaction type in a separate box. On the back side of the paper, write the sample equation on the corresponding area for each reaction type. As you have time, cut out the cards for studying.

Examples of Synthesis ReactionsExamples of Synthesis Reactions  Metal + Nonmetal 2 Na+ Cl 2  2 NaCl  Two nonmetalsS + O 2  SO 2  Nonmetal oxide + water  acidSO 2 + H 2 O  H 2 SO 3  Metal oxide + water  baseCaO + H 2 O  Ca(OH) 2  Example of Decomposition Reactions CaCO 3  CaO + CO 2  Examples of Combustion Reactions 2 Mg + O 2  2 MgO C 3 H 8 + 5O 2  3CO H 2 O

Single Replacement ReactionsSingle Replacement Reactions  Also called Single Displacement Rxn. Example: Cu + 2 AgNO 3  2 Ag + Cu(NO 3 ) 2 Metals Whether or not one metal will replace another can be determined by consulting the Activity Series of Metals. A reactive metal will replace any metal BELOW it in the activity series.

 In order for the reaction to occur, the lone element must be above the element in the compound  Otherwise…NO REACTION Will the following reactions occur? If so, complete and balance the reaction. Ag + Cu(NO 3 ) 2  Mg + AlCl 3 

Nonmetals  A nonmetal can also displace another nonmetal from a compound. This replacement is usually limited to the halogens (group 7A) and the reactivity decreases as you go down the periodic table.

Will the following reactions occur? If so, complete and balance the reaction. Br 2 + MgCl 2  F2 + MgCl2 

Double Replacement Reactions Double Replacement Reactions  Also called Double Displacement Reaction  Anions of two different compounds switch places, forming two new compounds.  Generally occur between two ionic compounds in aqueous solution and usually form a  precipitate,  gas, or  molecular compound Example: Na 2 CO AgNO 3  2 NaNO 3 + Ag 2 CO 3