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Chapter 7 Chemical Reactions
Objectives • Explain what a chemical reaction is • Describe indications of chemical reactions • Use state symbols in reactions • Write balanced chemical equations
What is a Chemical Reaction? • One or more substances are converted into new substances • New substances must be formed!!!
All Chemical Reactions • have two parts • Reactants - the substances you start with • Products- the substances you end up with • The reactants turn into the products. • Reactants ® Products
Indications of Reactions • Change in Heat - Exothermic or Endothermic Reactions • Light • Production of a Gas – Does not need to smell • Formation of a Precipitate -Precipitate is a solid that is produced as a result of a chemical rxn in solution
In a Chemical Reaction • The way atoms are joined is changed • Atoms aren’t created of destroyed. • Can be described several ways • In a sentence • Copper reacts with chlorine to form copper (II) chloride. • In a word equation • Copper + chlorine ® copper (II) chloride
Chemical Equation • Represents with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical rxn.
Symbols In Equations • An arrow separates the reactants from the products • Read “reacts to form” or “yields” • The plus sign = “and” • (s) = solid • (g) = gas • (l) = liquid • (aq) = aqueous solution • Dissolved in water
Δ Cu 2.0 atm Symbols In equations • = reversible reactions • Equilibrium (More later) • = Reaction is heated • = Catalyst is used (Copper) • Catalysts speed up reactions but are not consumed. • Enzymes are biological catalysts • = Specific Pressure • 2.00 atmospheres (1 atm is normal)
How Do Reactions Happen? • Simple View • Particles must collide
Reactions Continued • Particles are moving (Kinetic Energy) -Higher temperature means a higher speed • Particles collide -Energy is absorbed by particles -Bonds are broken -New bonds are formed -Energy is released
Diatomic Elements • 7 elements ALWAYS exist in diatomic state • Diatomic = 2 atoms • H2 , N2 , O2 , F2 , Cl2 , Br2 , I2 • Elements in –ogen and –ine • 1 + 7 pattern on the periodic table
Converting To Formula Equ. • You will often have to convert word equations to formula equations. • Determine the reactants and products • Covert the words to equations • Include any state symbols that are given • If no state are given don’t worry about them.
Converting To Formula Equ. • Sodium metal and chlorine gas react to form solid sodium chloride
Converting To Formula Equ. • A solution of hydrochloric acid and solid sodium carbonate react to form solid sodium chloride and gaseous carbon dioxide and water vapor.
Convert To a Sentence • Fe(s) + O2(g) ® Fe2O3(s) • Solid Iron and gaseous oxygen yields solid iron (III) oxide
Convert To a Sentence • Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq) • Solid Copper and a solution of silver nitrate yields solid silver and a solution of copper (II) nitrate
Balanced Equation • Law of Conservation of Mass states “Mass cannot be created or destroyed.” • Thus, atoms can’t be created or destroyed • So, a balanced equation has the same number of each element on both sides of the equation. • Balance equations with coefficients • Number in front of a formula (Multiplier)
Is This Equation Balanced? H2 + I2 HI
NO WAY! • Hydrogen and Iodine – 2 reactant atoms only 1 product atom
Balance With Coefficients • If there are 2 HI molecules the equation is balanced.H2 + I2 2HI
Don’t Change the Formula • You make a different compound!!!!!
Writing Balanced Equations • Write the correct formulas for all the reactants and products • Count the number of atoms of each type appearing on both sides • Balance the elements one at a time by adding coefficients (the numbers in front) • Check to make sure it is balanced.
Never • Never change a subscript to balance an equation. • If you change the formula you are describing a different reaction. • H2O is a different compound than H2O2 • Never put a coefficient in the middle of a formula • 2 NaCl is okay, Na2Cl is not.
Examples • H2 +O2 H2O
Examples • Ca(NO)3 + NaI CaI2 + NaNO3
Examples • C2H6 + O2 CO2 + H2O
Homework • p. 264 #23,25,26,28,30-33
Objectives • Predict a reaction type • Predict the products of a reaction • Use the activity series • Predict solubility of compounds
Types of Reactions Predicting the Products
Types of Reactions • There are millions of reactions. • Can’t remember them all • Fall into several categories. • We will learn 5 types. • Will be able to predict the products. • For some we will be able to predict whether they will happen at all. • Will recognize them by the reactants
#1 Synthesis Reactions • Combine - put together • 2 elements, or compounds combine to make one compound. • Ca +O2® CaO • SO3 + H2O ® H2SO4 • We can predict the products if they are two elements. • Mg + N2® Mg3N2
#2 Decomposition Reactions • decompose = fall apart • one reactant falls apart into two or more elements or compounds. • NaCl ® Na + Cl2 • CaCO3® CaO + CO2
#3 Single Replacement • One element replaces another • Reactants must be an element and a compound. • Products will be a different element and a different compound. • Na + KCl ® K + NaCl • F2 + LiCl ® LiF + Cl2
#3 Single Replacement • We can tell whether a reaction will happen • Some are more active than other • More active replaces less active • Higher on the list replaces lower. • If the element by itself is higher, it happens, in lower it doesn’t
Lithium • Potassium • Calcium • Sodium • Magnesium • Aluminum • Zinc • Chromium • Iron • Nickel • Lead • Hydrogen • Bismuth • Copper • Mercury • Silver • Platinum • Gold Activity Series • Halogens - • F2 • Cl2 • Br2 • I2
#3 Single Replacement • What does it mean that Au And Ag are on the bottom of the list? • Nonmetals can replace other nonmetals • Limited to F2 , Cl2 , Br2 , I2 • The order of activity is that on the table. • Higher replaces lower.
Solubility • Some compounds dissolve in water. • We say they are Soluble • Examples • Sodium Chloride, Potassium Nitrate • Some compounds do not dissolve • We say they are Insoluble • Form Precipitates
Solubility Rules • Solubility Rules are a general list that tells us what kind of compounds are soluble or insoluble. • Follow from beginning to end • Rule one has precedence over rule two
Solubility Rules • All Acids are soluble • Most nitrate and acetate salts are soluble. • Most salts containing the alkali metal ions (Li+, Na+, K+, Cs+, Rb+) and the ammonium (NH4+) ion are soluble. • Most chloride, bromide and iodide salts are soluble. Exceptions are salts containing the ions Ag+, Pb2+, and Hg2+. • Most sulfate salts are soluble. Notable exceptions are BaSO4, PbSO4, HgSO4 and CaSO4.
Solubility Rules • Most hydroxide salts are insoluble. • Most sulfide (S2-), carbonate (CO32-), chromate (CrO42-) and phosphate (PO43-) salts are insoluble
Solubility Rules • M I Soluble? • Potassium Bromide • Yes • Iron (III) Sulfate • Yes • Calcium Phoshate • No • Zinc Acetate • Yes
#4 Double Replacement • Two things replace each other. • Reactants must be two ionic compounds or acids. • Usually in aqueous solution • NaOH + FeCl3® Fe(OH)3 + NaCl
#4 Double Replacement • Will only happen if one of the products • doesn’t dissolve in water and forms a solid • or is a gas that bubbles out. • or is a covalent compound usually water.
Examples • H2 + O2® • H2O ® • Zn + H2SO4® • HgO ® • KBr +Cl2® • AgNO3 + NaCl ® • Mg(OH)2 + H2SO3®
Last Type • Combustion • A compound composed of only C H and maybe O is reacted with oxygen • If the combustion is complete, the products will be CO2 and H2O. • CH4 + O2 CO2 + 2H2O
How to recognize which type • Synthesis – Only one product • Decomposition – Only one reactant • Single replacement – Element and Compound as reactants • Double replacement – Two compounds • Combustion – Something reacting with oxygen
Homework • p. 264 #'s 35 37-40, 46 without net ionic