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

Precipitate!

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

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) Δ Cu 2.0 atm

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

Diatomic Elements

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

Predicting the Products 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

Activity Series Halogens - F2 Cl2 Br2 I2 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 Iron (III) Sulfate Yes Iron (III) Sulfate Calcium Phoshate No Zinc Acetate

#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

Objectives Predict the type of double replacement reaction Write net ionic equations

More on Double Replacement Three Main Types Precipitation (A solid forms) Gas Forming (A gas forms) Neutralization Reaction of Acid and Base

Precipitation One of the products will be a solid Determined by solubility rules That’s it.

Gas Forming You see bubbles! Usually from decomposition of Carbonic Acid - H2CO3  CO2 + H2O Sulfurous Acid - H2SO3  SO2 + H2O When you get one of these as a product replace it with the gas and water. Ex. HNO3 Na2CO3  H2CO3 + NaNO3 Products become CO2 + H2O + NaNO3

Neutralization Reaction of Acid and a Base Acid usually starts with H Base usually has hydroxide OH- Product is salt and water Ex HF + KOH HOH +KF

Dissociation Ionic Compounds separating into ions AgNO3(aq)+Na2S(aq)Ag+ +NO3- +2Na+ +S-2

Net Ionic Equations Used to remove “unimportant” reactants and products What’s “unimportant” Whatever is not used to make precipitates, liquids, or gases They are spectator ions

Net Ionic Rules Dissociate all soluble compounds According to balanced equation Leave all solids, liquids, and gasses Cross out common terms (Same) Rewrite as net ionic

Example Solutions of lead (II) nitrate & hydrochloric acid are in beakers. Draw what in is in the beakers.

Example Solutions of lead (II) nitrate & hydrochloric acid are mixed. Write the balanced equation

Example Draw what is in the beaker when the two solutions are mixed.

Example Solutions of lead (II) nitrate & hydrochloric acid are mixed. Write the net ionic equation

Example Solutions of copper (II) nitrate and sodium sulfide are mixed. Write the net ionic equation.

Homework p. 266 #'s 46,62ab,68,75,82,98