Chemical Reactions Chapter 10 Slide 2 Part I: Counting Atoms How
Many Atoms in a Molecule? Slide 3 Counting Atoms Most substances
that we encounter are compounds, not elements. A chemical compound
is a pure substance formed from the combination of two or more
different elements. The properties of the compound may be
completely unlike those of the elements that form it. The formula
for a compound lists the symbols of the individual elements
followed by subscripts which indicate the number of atoms of that
element. (If no subscript is given, it is understood to be 1.)
E.g., NaCl, H 2 O, C 12 H 22 O 11. Slide 4 Counting Atoms A
molecular formula gives the actual number of atoms of each element
in a molecule of a compound. Hydrogen peroxide H 2 O 2 Water H 2 O
Glucose C 6 H 12 O 6 A structural formula uses lines to represent
covalent bonds, and shows how the atoms in a molecule are joined
together: HOOH HOH O=C=O Slide 5 Counting Atoms Example: How Many
Atoms? Example: How Many Atoms? 2 Hs and 2 Os = 4 atoms
H2O2H2O2H2O2H2O2 2 Cs+ 5 Hs + 1 Os + 1 H = 9 atoms C 2 H 5 OH 3
Ks+1 Ps + 4 Os = 8 atoms K 3 PO 4 6 Cs + 12 Hs + 6 Os = 24 atoms C
6 H 12 O 6 Slide 6 Counting Atoms with Polyatomic Ions - Al 2 (SO 4
) 3 Al S O O O O S O O O O S O O O O = 17 ATOMS Slide 7 Counting
Atoms with Polyatomic Ions When counting atoms with polyatomic
ions; When counting atoms with polyatomic ions; Count number of
atoms in one polyatomic ion o Ions inside the parentheses Multiply
by number of polyatomic groups in the molecule (number outside the
parenthesis) Examples: Examples: Al 2 (SO 4 ) 3 - 2 Als + 3(1 S + 4
Os) = 2 + 3(5) = 2+15 = 17 atoms Mg(NO 3 ) 2 1 Mg + 2(1 N + 3 Os) =
1 + 2(4) = 1+8 = 9 atoms Slide 8 Hydrates Hydrates are ionic
compounds which also contain a specific number of water molecules
associated with each formula unit. The water molecules are called
waters of hydration. The formula for the ionic compound is followed
by a raised dot and #H 2 O Example: MgSO 47H 2 O. They are named as
ionic compounds, followed by a counting prefix and the word hydrate
CuSO 45H 2 O copper(II) sulfate pentahydrate BaCl 26H 2 O barium
chloride hexahydrate MgSO 47H 2 O magnesium sulfate heptahydrate
(Epsom salts) Slide 9 How Many Atoms in a Hydrate? When counting
atoms in the hydrate, count the water atoms also. When counting
atoms in the hydrate, count the water atoms also. Example: Example:
CuSO 45H 2 O o o 1 Cu + 1 S + 4 Os + 5(2 Hs + 1 Os) o o =1+1+4+5(3)
o o = 6+15 = 21 atoms BaCl 26H 2 O o 1 Ba + 2 Cl + 6(2 Hs + 1 Os) o
= 1+2+6(3) o =3 + 18 = 21 Atoms Slide 10 Part II: Conservation of
Mass Slide 11 Conservation of Mass In a normal chemical reaction,
the mass of substances in a closed system will remain constant, no
matter what processes are acting inside the system. In a normal
chemical reaction, the mass of substances in a closed system will
remain constant, no matter what processes are acting inside the
system. How ever many atoms a reaction starts with, ends with the
same number. Atoms dont change their identity in a chemical
reaction Number of atoms for EACH ELEMENT STAYS THE SAME in a
chemical reaction The elements just rearrange their organization
The beginning MASS of the reaction EQUALS the ending MASS of the
reaction Slide 12 Conservation of Mass Total Mass stays the same in
a chemical reaction Total Mass stays the same in a chemical
reaction 2g H 2 + 16g O 2 yields 18g H 2 O Number and Identity of
Atoms stays the same in a chemical reaction Number and Identity of
Atoms stays the same in a chemical reaction 2 2 H 2 + 1 O 2 yields
2 H 2 O H H H H O OH H O H H O Slide 13 Part III: Writing Reactions
How Do You Write a Chemical Reaction? Slide 14 III. Chemical
Reactions Definition process by which the atoms of one or more
substances are rearranged Definition process by which the atoms of
one or more substances are rearranged KEY: new substances are
formed KEY: No Atoms are Gained or Lost A chemical reaction is the
process by which atoms of one or more substances are rearranged
into new substances A chemical reaction is the process by which
atoms of one or more substances are rearranged into new substances
Chemical change occurs How do you know? Slide 15 III. Evidences of
a Chemical Reaction 1) gas production 2) light production 3)
temperature change (endo/exothermic) 4) precipitate formed (solid
from 2 liquids) 5) permanent color change Slide 16 Energy is stored
in compounds as chemical potential energy Energy is stored in
compounds as chemical potential energy due to specific arrangements
of atoms. A chemical reaction changes the potential energy present.
A chemical reaction changes the potential energy present. III.
Energy Changes Slide 17 When energy is gained; heat is added for a
reaction to occur. These are called ______________________,When
energy is gained; heat is added for a reaction to occur. These are
called ______________________, Energy Changes exothermic reaction
endothermic reactions These reactions get hotter. When energy is
lost as heat, it is called an __________________.When energy is
lost as heat, it is called an __________________. These reactions
get colder. Energy in a reaction is shown with: H (heat) kJ Joules
Heat energy Slide 18 III. Chemical Reactions Representing Chemical
Reactions: Representing Chemical Reactions: Reactants the stuff you
start with An arrow which means yields, or becomes Products the
stuff you end up with Principle of Conservation of Mass applies to
chemical reactions. Principle of Conservation of Mass applies to
chemical reactions. Why? Slide 19 III. Chemical Reactions Word
Equations: Word Equations: Reactant-A + Reactant-B yields
Product-AB Example: o Sodium(s) + Chlorine(g) Sodium Chloride(s) o
The small letters in paretheses () indicate the state of the
reactant or product (solid, liquid, gas, or aqueous solution) (s) =
solid (l) = liquid (g) = gas (aq) = aqueous = dissolved in water
Slide 20 Part IV: Balancing Equations Applying Conservation of Mass
to Equations Slide 21 VI. Chemical Equations Step 1: Write a
Skeleton Equation Step 1: Write a Skeleton Equation Skeleton
Equation uses chemical formulas and symbols instead of words:
Skeleton Equation uses chemical formulas and symbols instead of
words: Words: Sodium + Chlorine gas yields Sodium Chloride Symbols:
Na(s) + Cl 2 (g) NaCl Skeleton Equations are not complete
equations, but are the first step in writing a complete equation
Slide 22 IV. Chemical Equations Chemical Equation is BALANCED
Chemical Equation is BALANCED Balanced means that conservation of
mass is upheld All atoms in reactants are also in products o No
more, no less o Just rearranged Slide 23 IV. Chemical Equations
Balancing Equations Balancing Equations Use a number before the
compound/element symbol to indicate how many of them are needed o
Called a COEFFICIENT o Written in front of the atom/compound o KEY:
Coefficient is a MULTIPLIER Number of atoms per molecule is
SUBSCRIPT Change ONLY the COEFFICIENTS to balance the equation
Slide 24 IV. Chemical Reactions Steps to Balance Equations Steps to
Balance Equations 1. Write the skeleton equation 2. Count the atoms
of EACH element in the reactants 3. Count the atoms of EACH element
in the products 4. Change the coefficients to make the number of
atoms of each element equal on both sides of the equation 5. Write
the coefficients in the lowest possible ratio 6. Check your work
NEVER CHANGE A SUBSCRIPT NEVER CHANGE A SUBSCRIPT Slide 25 IV.
Chemical Equations 1.Write the skeleton equation: Al + O 2 Al 2 O 3
2. Count Number of atoms for each element on both sides This is not
balanced because the numbers dont match 3. Multiply coefficients
until they match multiply the entire units 2 Al + O 2 Al 2 O 3 Go
to 6 Oxygens Slide 26 IV. Balancing Equations Al + O 2 2 Al 2 O 3 4
3 Al + 2 Al 2 O 3 O2O2 Multiply each atom by 2 Slide 27 IV.
Balancing Equations 2 The work of balancing a chemical equation is
in many ways a series of trials and errors. Consider the equation
given below. Does this represent a balanced chemical equation? N 2
+ H 2 NH 3 Slide 28 IV. Balancing Equations 3 To balance this
reaction, it is best to choose one kind of atom to balance
initially. Let's choose nitrogen in this case. 2 Nitrogen Atoms in
Reactants requires 2 Ammonia molecules in Product to balance the
nitrogen 2NH 3 H2H2 +N2N2 Slide 29 IV. Balancing Equations 2 Once
we know what the molecules are (N2, H2, and NH3 in this case) we
cannot change them (only how many of them there are). The nitrogen
atoms are now balanced, but there are 6 atoms of hydrogen on the
product side only 2 of them on the reactant side. The next step
requires multiplying the number of reactant hydrogen molecules by
three to give: N2N2 2NH 3 H2H2 + 3H 2 Slide 30 IV. Dont Forget:
Diatomic Elements Definition 7 elements that NEVER occur as
singular atoms (always paired with an the same or different
element) Definition 7 elements that NEVER occur as singular atoms
(always paired with an the same or different element) H2 O2 F2 Br2
I2 N2 Cl2 Ex: 2 HCl + 2K 2 KCl + H 2 Slide 31 IV. Balancing
Equations 3 1. Start with an unbalanced equation 2. Draw boxes
around the compounds so you dont mess with the groups Dont be
threatened by how complex it looks! Slide 32 IV. Balancing
Equations 2 3. Make an element inventory count number of atoms for
each element on each side of the equation Slide 33 IV. Balancing
Equations 3 4. Write coefficients in front of each of the boxes
until the inventory for each element is the same both before and
after the reaction Save Oxygen and Hydrogen for last, Treat
Polyatomic like an atom. Lets start with Sodium N Y Y N We have 2
in products, so I need 2 in reactants Multiply reactant with sodium
by 2 and recount atoms 23 11 11 21 H SO 4 O Na
ProductReactantElement Balanced? 1 2 Y 3 4 N Slide 34 IV. Balancing
Equations 3 Inventory Shows: Reactant side has FOUR hydrogen atoms
Product side has TWO hydrogen atoms Using your amazing powers of
mathematics two hydrogen multiplied two becomes four hydrogen N Y N
Y 24 11 12 22 H SO 4 O Na ProductReactantElement Balanced? 1 2 Y 2
4 Y Slide 35 Helpful Hints Balance hydrogen and oxygen last Balance
hydrogen and oxygen last Balance polyatomic ions as a group if
present on both reactants and products Balance polyatomic ions as a
group if present on both reactants and products You can consider a
polyatomic ion as a single element If the balancing starts to get
very complex: If the balancing starts to get very complex: Stop
Start over Select a different atom to balance first. Slide 36
Example Using PolyAtomics Before Before MgCl 2 + NaOH Mg(OH) 2 +
NaCl 1 Mg 2 Cl1 Cl 1 Na 1 OH2 OH MgCl 2 + 2 NaOH Mg(OH) 2 + 2 NaCl
1 Mg 2 Cl 2 Na 2 (OH) After After Slide 37 Types of Chemical
Reactions Part V Slide 38 Classifying Chemical Reactions Synthesis
Synthesis Decomposition Decomposition Single replacement Single
replacement Double Replacement Double Replacement Combustion
Combustion Slide 39 Synthesis Definition two or more substances
react to form ONE product Definition two or more substances react
to form ONE product Product is usually bigger or more complex than
either reactant A + B AB Slide 40 Hey baby lets get jiggy. Slide 41
Synthesis reaction of two elements reaction of two elements ___ Al
+ ___ Cl 2 ___ AlCl 3 Al 3+ Cl 1- 223 Slide 42 reaction of two
compounds reaction of two compounds reaction of element and
compound reaction of element and compound Synthesis CaO + H 2 O
Ca(OH) 2 SO 2 + O 2 SO 322 Slide 43 Decomposition definition one
substance breaks down into two or more simpler products definition
one substance breaks down into two or more simpler products AB A +
B Slide 44 Break yoself fool! Slide 45 Decomposition Example
reaction: Example reaction: __ NaN 3 (s) ___ Na (s)+ ___ N 2 (g)
223 __ CaO (s) ___ Ca (s)+ ___ O 2 (g) 221 Slide 46 Single
Replacement Reactions Definition one element replaces another
element in a compound to form new compound Definition one element
replaces another element in a compound to form new compound A + BX
AX + B Slide 47 Im gon dance with yo lady Slide 48 Double
Replacement Defn exchange of cations between two ionic compounds
Defn exchange of cations between two ionic compounds A B + C D AD +
CB switch Slide 49 Slide 50 3 possible products of double
replacement reactions Precipitate Precipitate Gas Gas Water Water
Slide 51 Reactivity Series (or Activity Series) More active will
replace less active More active will replace less active Less
active will NOT replace more active metals metals Li K Ca Na Mg Al
Mn Zn Fe Ni Sn Pb Cu Ag Au most active least active F Cl Br I most
activeleast active halogens halogens Slide 52 examples aluminum +
iron (III) oxide aluminum + iron (III) oxide Al Fe 2 O 3 +
Stronger? Al 3+ O 2- Al 2 O 3 Fe + Fe 3 + O 2- 2 211 Slide 53
examples silver + copper (I) nitrate silver + copper (I) nitrate Ag
CuNO 3 + Stronger? Cu 1 + NO 3 1- NO RXN Slide 54 examples fluorine
gas + sodium bromide fluorine gas + sodium bromide F2F2 NaBr +
Stronger? Br 2 NaF+ Na 1 + F 1- 2211 Slide 55 examples chlorine gas
+ hydrogen fluoride chlorine gas + hydrogen fluoride Cl 2 HF +
Stronger? NO RXN Slide 56 Example Problem lithium iodide and
aqueous silver nitrate react lithium iodide and aqueous silver
nitrate react Li 1+ I 1- Ag 1+ NO 3 1- Li I AgNO 3 LiNO 3 Ag I (s)
+ + Slide 57 Combustion definition compound reacts with O 2
definition compound reacts with O 2 Hydrocarbon compound w/ only
carbon and hydrogen Hydrocarbon compound w/ only carbon and
hydrogen Slide 58 Combustion Combustion of hydrocarbons ALWAYS
produces CO2 and H2O C x H y + O 2 CO 2 + H 2 O Slide 59 Ex problem
show combustion of propane (C 3 H 8 ) gas show combustion of
propane (C 3 H 8 ) gas C3H8C3H8 O2O2 CO 2 H2OH2O++1534 I sell
propane and propane accessories!
