Chapter 11 Chemical Reactions Hingham High School Mr. Dan Clune

All chemical reactions Two parts: Reactants – what you start with Products- what you end with Reactants turn into the products. Reactants ® Products

The way atoms are joined is changed. In a chemical reaction The way atoms are joined is changed. Atoms aren’t created or destroyed.

In a chemical reaction Can be described several ways: 1. In a sentence Copper reacts with chlorine to form copper (II) chloride. 2. In a word equation Copper + chlorine ® copper (II) chloride

Symbols in equations-p.323 Cu + Cl2  CuCl2 Arrow () separates reactants from products Read “reacts to form” Plus (+) sign read “and”

Symbols used in equations Cu(s) + Cl2(g)  CuCl2(s) (s) = solid (g) = gas (l) = liquid (aq) - dissolved in water, an aqueous solution.

Symbols used in equations ­ ↑ after product, indicates gas produced same as (g) - H2↑ ¯ after product, indicates solid produced same as (s) - PbI2↓

Symbols used in equations indicates reversible reaction shows that heat is supplied to the reaction is - indicates a catalyst is supplied, in this case, platinum.

What is a catalyst? Speeds up a reaction Is NOT changed or used up by the reaction. Enzymes are biological or protein catalysts.

Skeleton Equation Uses formulas to describe a reaction doesn’t indicate how many. NOT balanced All chem equations are description of rxn.

Convert this to an equation Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas. Fe2S3(s) +  HCl(g) FeCl3 + H2S(g)

Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water, carbon dioxide gas, sodium nitrate dissolved in water. +  HNO3(aq) Na2CO3(aq) + + H2O(l) CO2(g) NaNO3(aq)

Now, read these: Fe(s) + O2(g) ® Fe2O3(s) Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq) NO2 (g) N2(g) + O2(g) Solid iron + oxygen gas yields solid iron (III) oxide. Solid copper + aqueous silver nitrate yields solid silver + aqueous copper (II) nitrate. Gaseous nitrite reacts with a platinum catalyst to form nitrogen gas and oxygen gas.

Balancing Chemical Equations

Balanced Equation Atoms can’t be created or destroyed All the atoms we start with we must end up with A balanced equation has the same number of each element on both sides of the equation.

® C + O2 ® CO2 This equation is already balanced What if it isn’t? O + 1 C and 2 O on each side.

® C + O2 ® CO Need one more O in the products. Can’t change the formula, because it describes what it is (carbon monoxide in this example)

® Must be used to make another CO But where did the other C come from? + C O C O Must be used to make another CO But where did the other C come from?

C C ® O O + O C C O Must have started with two C 2 C + O2 ® 2 CO

Finding the number of atoms The subscript in front of an element is the number of atoms of that element / polyatomic. Ex) CO2 B2(SO4)3 C= O= B= SO4= A coefficient in front of the formula multiplies the amount of elements by the coefficient. Ex) 3CO2 2B2(SO4)3 1 2 2 3 3 6 4 6

Finding the number of atoms H2O H= O= 2H2O B(NO3)2 B= NO3= 3B(NO3)2 Pb3(PO4)4 Pb= PO4= 2Pb3(PO4)4 2 1 4 2 1 2 3 6 3 4 6 8

Rules for balancing: . Determine the correct formulas for reactants and products. . Write a skeleton equation.

Rules for balancing: 3. Count the number of atoms of each element appearing on both sides of the equation. 4. Balance the elements one at a time by adding coefficients (the numbers in front) -Save H and O until LAST!

Rules for balancing: 5. Check to make sure it is balanced. 6. Make sure the coefficients are in the lowest possible ratio.

Don’t you ever… X Never change a subscript to balance an equation. H2O is a different compound than H2O2 Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not. X If you change the formula you are describing a different reaction.

Example 2 2 H2 + O2 ® H2O R P H O 2 1 4 4 2

2 2 H2 + O2 ® H2O

AgNO3 + Cu ® Cu(NO3)2 + Ag 2 2 NO3 Cu Ag P R 1 2 2 2 2

Mg + N2 ® Mg3N2 3 R P Mg N 1 2 3 3

P + O2 ® P4O10 4 5 R P O 1 2 4 10 4 10

Na + H2O ® H2 + NaOH 2 2 2 O H Na P R 1 2 3 2 2 4 4 2 2

CH4 + O2 ® CO2 + H2O 2 2 O H C P R 1 4 2 3 4 4 4

Section 11.2 Types of Chemical Reactions OBJECTIVES: Identify a reaction as combination, decomposition, single-replacement, double-replacement, or combustion

Types of Reactions 5 major types. predict the products predict whether or not they will happen at all How? We recognize them by their reactants *

#1 - Combination Reactions Combine - put together 2 or more substances combine to make one compound. A + B ® AB Ca +O2 ® CaO SO3 + H2O ® H2SO4

#1 - Combination Reactions We can predict the products if they are two elements. Mg + N2 ® 3 Mg N 3 2

Write and balance Ca + Cl2 ® Fe + O2 ® iron (II) oxide Al + O2 ® Remember that the first step is to write the correct formulas Then balance by using coefficients only CaCl2 2 2 FeO 4 3 2 Al2O3

#1 – Combination Reactions Additional Notes: a) Some nonmetal oxides react with H2O - produces acid: SO2 + H2O  H2SO3 b) Some metallic oxides react with H2O - produces base: CaO + H2O  Ca(OH)2 (how “acid rain” forms)

#2 - Decomposition Reactions Decompose = fall apart One reactant falls apart into two or more elements or compounds. AB  A + B

#2 - Decomposition Reactions NaCl Na + Cl2 CaCO3 CaO + CO2 Note that energy is usually required to decompose

#2 - Decomposition Reactions Binary compounds (made of 2 elements) falls apart into its elements H2O HgO 2 2 H2 + O2 2 Hg + O2 2

#2 - Decomposition Reactions If the compound has more than two elements, one product must be given. The other product will be from the missing pieces NiCO3 CO2 + H2CO3(aq) ® CO2 + ? Ni H2

#3 - Single Replacement Reactions One element replaces another (new dance partner) Reactants are an element & cpd Products will be a different element and different cmpd Li + KCl ® K + LiCl F2 +2 LiCl ® 2LiF + Cl2 (Cations switched) (Anions switched) *

#3 Single Replacement Reactions Metals replace other metals (and H) K + AlN ® Zn + HCl ® Think of water as: HOH Metals replace first H, then combines w/ hydroxide (OH). Na + H2O ® 3 K3N + Al 2 ZnCl2 + H2 2 2 NaOH + H2 2 *

#3 Single Replacement Reactions Sometimes, the reaction will not happen: Some chemicals are more “active” than others More active replaces less active *

The “Activity Series” of Metals Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold Higher activity If the lone metal is above the paired metal, replacement will occur. Ex) Li + NaCl ® Na + LiCl If the lone metal is below the paired metal, replacement will not occur. Ex) Na + LiCl ® Na + LiCl The more active metal wants another element to stabilize it. Lower activity

The “Activity Series” of Halogens Higher Activity If the lone halogen is above the paired halogen, replacement will occur. Fluorine Chlorine Bromine Iodine Lower Activity 2NaCl(s) + F2(g)  2NaF(s) + Cl2(g) MgCl2(s) + Br2(g)  No Reaction!

#3 Single Replacement Reactions Practice: Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold Higher activity Fe + CuSO4 ® Pb + KCl ® Al + HCl ® FeSO4 + Cu No reaction 2 6 2 AlCl3 + H2 3 Lower activity *

#4 - Double Replacement Reactions Two things replace each other. Reactants must be two ionic compounds. NaOH + FeCl3 ® positive ions change place NaOH + FeCl3 ® Fe+3 OH- + Na+1 Cl-1 = NaOH + FeCl3 ® Fe(OH)3 + NaCl *

#4 - Double Replacement Reactions Have certain “driving forces”, or reasons only happens if one product: a) doesn’t dissolve in water & forms solid (a “precipitate”), or b) is gas that bubbles out, or c) is molecular compound (usually water) *

Complete and balance: assume all of the following reactions actually take place: CaCl2 + NaOH ® CuCl2 + K2S ® KOH + Fe(NO3)3 ® K2SO4 + BaF2 ® 2 Ca(OH)2 + NaCl 2 CuS + KCl 2 3 3 KNO3 + Fe(OH)3 2 KF + BaSO4 *

How to recognize which type? Look at the reactants: El + El = Combination Cpd = Decomposition El + Cpd = Single replacement Cpd + Cpd = Double replacement *

Practice Examples: H2 + O2 ® H2O ® Zn + H2SO4 ® HgO ® KBr + Cl2 ® AgNO3 + NaCl ® Mg(OH)2 + H2SO3 ® 2 2H2O 2 2 H2 + O2 H2 + ZnSO4 2 2 Hg + O2 2 2 KCl + Br2 AgCl + NaNO3 MgSO3 + H2O 2 *

#5 – Combustion Reactions Combustion means “add oxygen” Normally, a cpd composed of only C, H, (sometimes O) is reacted with oxygen – called “burning” Complete combustion, products are CO2 and H2O If incomplete, products are CO and H2O *

Combustion Reaction Examples: C4H12 + O2 ® C6H12O6 + O2 ® C8H8 + O2 ® 7 4 CO2 + H2O 6 9 6 CO2 + H2O 6 10 8 CO2 + H2O 4 *

SUMMARY: An equation... Describes a rxn Must be balanced only balance by changing coefficients special symbols to indicate physical state, catalyst or energy required, etc. *

Reactions 5 major types We can tell what type they are by looking at reactants Single Replacement happens based on the Activity Series *

Section 11.3 p. 342 Reactions in Aqueous Solution KMnO4 Co(NO3)2 NiCl2 CuSO4 K2Cr2O7 K2CrO4

Net Ionic Equations Many reactions occur in water, or aqueous solution When dissolved in water, many ionic cpds “dissociate”, or separate, into cations & anions Now write ionic equation

Net Ionic Equations Example (needs to be a double replacement reaction) AgNO3 + NaCl  AgCl + NaNO3 1. this is the full balanced equation 2. next, write it as ionic equation by splitting the cpds into their ions: Ag1+ + NO31- + Na1+ + Cl1-  AgCl(s) + Na1+ + NO31- Solids do not split up.

Net Ionic Equations 3. Crossing out ions that did not change (called spectator ions) Ag1+ + Cl1-  AgCl (s) This is the net ionic equation Let’s talk about precipitates before we do some other examples

Predicting the Precipitate Insoluble salt is a precipitate i.e. a solid General solubility rules are found: Table 11.3, p. 344 in textbook

Solubility Rules

BaCl2 + AgNO3 → Break up into ions Now write the net ionic equation. 2 Ba(NO3)2 + AgCl (s) 2 Ba+2 + 2Cl- + 2Ag+ + 2NO3-  Ba+2 + 2NO3- + 2AgCl (s) 2Ag+ + 2NO3-  2AgCl (s)

Now write the net ionic equation. 2 NaCl + Ba(NO3)2 → 2 NaNO3 + BaCl2 Break up into ions Now write the net ionic equation. 2Na+ + 2Cl- + Ba+2 + 2NO3-  2Na+ + 2NO3- + Ba+2 + 2Cl- Nothing changed, so no net ionic equation.

PbCl2 (s) + Li2O  PbO + LiCl 2 Break up into ions Now write the net ionic equation. PbCl2 (s) + 2Li+ + O-2  Pb+2 + O-2 + 2Li+ + 2Cl- PbCl2 (s)  Pb+2 + 2Cl-