Matter and Change 11.1 Describing Chemical Reactions Chapter 11 11.2 Types of Chemical Reactions 11.3 Reactions in Aqueous Solution

Reaction(explosion of alkali metals) http://www.youtube.com/watch?v=HvVUtpdK7xw

11.1 Chemical Reactions Examples of Chemical Reactions Rusting of iron Burning (combustion) of wood Cooking Vinegar + Baking soda -> Photosynthesis 6CO2 + 6H2O + Energy --> C6H12O6 + 6O2

Chemical reactions are like sentences. Symbols  elements Formula  compound Equations  chemical reactions Put letters together to make words. Put words together to make sentences.

Chemical reaction a reaction that occurs when the atoms of one of more substances are rearranged to form different substances a chemical change Evidence of a chemical reaction - Temperature change - Color change - Odor produced - Formation of bubbles - Appearance of a solid

Chemical Equations 2H2(g) + O2(g) 2H2O (l) Reactants: elements or compounds to the left of the arrow that combine together in a chemical reaction Products: elements or compounds to the right of the arrow that are produced in a chemical reaction Coefficient: whole number before a chemical formula Subscript: small lowered number after a chemical symbol + : represents “and” : direction reaction progresses, yields or produces

C(s) + O2(g) CO2 (g) physical states of reactants and products are indicated by: (s) = solid:    C(s) (g) = gas:    CO2(g)  (l) = liquid:    H2O(l) (aq) = aqueous, dissolved in water, NaCl(aq) is a salt water solution (cr) = crystalline = precipitate forms

Chemical Equations 2H2(g) + O2(g) 2H2O (l) Identify the following and label Reactants: Products: Coefficient: Subscript: + define define

Covalent Bonding GEN-U-INE A molecule is a neutral group of atoms joined together by covalent bonds. Diatomic molecules – molecules made up of the same element Examples: O2 , H2 , N2, F2 , Cl2 , Br2 , I2 GEN-U-INE

Word and Formula Equations Skeleton equation represents the reactants and products of a chemical reaction by their formulas. Example: Na(s) + Cl2(g) NaCl(s)

Balancing Chemical Equations balanced chemical equation – shows that each side of the equation has the same number of atoms of each element and mass is conserved 2 Na(s) + Cl2(g) 2 NaCl(s) Law of conservation - in a chemical reaction matter is neither created nor destroyed Chemical equations must be balanced using coefficients

Balancing Equations ____ K + ____ Cl2  ____ KCl ____ Ag + ____ O2  ____ Ag2O ____ H2 + ____ O2  ____ H2O ____ Na + ____ MgF2  ____ NaF + ____ Mg ____ N2 + ____ H2  ____ NH3

Balance the following equations Mg + O2 ----> MgO KClO3 ----> KCl + O2 Na + MgCl2 ----> NaCl + Mg

Word and Formula Equations A word equation is an equation represented by words. Example: solid sodium plus chlorine gas reacts to produce sodium chloride

Steps for Balancing Equations 1) Write skeleton equation: assemble the correct formulas 2) Count the number of atoms of elements in reactants 3) Count the number of atoms of elements in products 4) Balance the elements one at a time by adding coefficients in front of a formula to make number of atoms equal on both sides of equation 5) Check to make sure equation is balanced and coefficients are in lowest possible ratio

Sample problems – Balancing Equations Word Equation Hydrogen plus oxygen yields water Skeleton Equation Balanced Equation

Sample problems – Balancing Equations Word Equation Fluorine plus calcium bromide yields calcium fluoride and bromine Skeleton Equation Balanced Equation

Water and iron react to form iron III oxide and hydrogen Propane (C3H8) burns in oxygen to form carbon dioxide and water

Do-Now Identify and write the polyatomic ion using your ion chart. Include charge! sulfate – 3. hydroxide – nitrate – 4. phosphate – Write the formulas for the following compounds. Must show charge and crisscross! Potassium oxide 3. Iron (III) hydroxide Calcium chloride 4. Barium sulfate

Chemical Reactions 11.3 Reactions in Aqueous Solution Chapter 11 Chemical Reactions 11.1 Describing Chemical Reactions 11.2 Types of Chemical Reactions 11.3 Reactions in Aqueous Solution Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What happens to the wax when you burn a candle? CHEMISTRY & YOU What happens to the wax when you burn a candle? When you burn a candle, a chemical reaction called combustion takes place. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Classifying Reactions What are the five general types of reactions? Synthesis (or combination) Decomposition Singe-replacement Double-replacement Combustion Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

1. Synthesis Reactions (Combination) Two (or more) reactants combine to form one product general form: A + B AB specific types: 2 elements Fe + S Fe+2S-2 2 compounds Ca+2O-2 + H2O Ca+2(OH)-12 1 element, 1 compound 2SO2 + O2 2SO3

2. Decomposition Reactions one reactant breaks down into two or more products general form: AB A + B Examples: 2Na+1N-3 6Na + N2 Ca+2(CO3)-2 Ca+2O-2 + CO2 *decomposition reactions require energy heat ---> electricity ---> catalyst ---> 3

Classify each reaction as Synthesis or Decomposition _________________ 2 Na + Cl2 ---> 2NaCl _________________ CaCO3 ---> CaO + CO2 _________________ 2H2O ---> 2H2 + O2 _________________ 2CO + O2 ---> 2CO2

3. Single-Replacement A single-replacement reaction is one in which one element replaces a second element in a compound general form: Ao + B+C- Bo + A+C- Example: Zn + Cu+2(NO3)-1 Cu + Zn+2(NO3)-1 general form: B+C- + Do B+D- + Co Example: 2Na+Cl- + Br2 2 2 2Na+Br- + Cl2

4. Double-Replacement general form: A+B- + C+D- ---> A+D- + C+B- 2 3 general form: A+B- + C+D- ---> A+D- + C+B- Ex.: Na+(CO )-2 + Ba+2Cl-1 ---> 2Na+Cl-1 + Ba+2(CO )-2 Specific type: Neutralization Ca(OH)2 + 2HCl ---> CaCl2 + 2H2O base + acid yields salt + water 2 3 2 3

Classify each reaction as Single Replacement or Double Replacement __________ Mg + Ag2SO4 ---> MgSO4 + 2Ag __________ 2NaF + CaCO3 ---> Na2CO3 + CaF2 __________ SrBr2 + 2KOH ---> Ca(OH)2 + 2KBr __________ 2LiCl + Br2 ---> Cl2 + 2LiBr

Combustion Rxns Ex: CH4 + 2 O2 CO2 + 2 H2O -a reactant (hydrocarbon) and oxygen, O2 react and release energy, heat, and/or light, and products formed are CO2 and H2O Ex: CH4 + 2 O2 CO2 + 2 H2O

Endothermic and Exothermic Reactions We can indicate if energy was present in the reaction Reactions that have energy as a reactant are called endothermic - They require energy for the reaction to occur - Also sometimes represented as → or → Reactions that have energy as a product are called exothermic - Energy happens as a result of the reaction heat

Do Now Quiz on Balancing and Word Equations Practice problems 1. Aluminum bromide + chlorine yield aluminum chloride and bromine Zinc nitrate + lead yield lead (II) nitrate + zinc Potassium chlorate when heated yields potassium chloride + oxygen gas