Transcript Chapter 11 Chemical Reactions
1 Chapter 11
“Chemical Reactions”
2
Section 11.1
p. 321 Describing Chemical Reactions
All chemical reactions… have two parts:
1. Reactants
start with = substances you
2. Products
= end with reactants turn into products Reactants Products 3
4
Products Reactants - Page 321
In a chem rxn Atoms not created or destroyed (Law of Conservation of Mass) rxn described in a: #1.
sentence
every item is a word Copper reacts with chlorine to form copper (II) chloride.
#2.
word equation
Copper + chlorine some symbols used copper (II) chloride 5
Symbols in equations? – Text page 323 arrow ( →) separates reactants from products (points
to
products) –Read as: “reacts to form” or yields plus sign = “and” (s) after formula = solid: (g) = gas: (l) = liquid: Fe
(s)
CO
2(g)
H
2
O
(l)
6
Symbols used in equations (aq) after formula = dissolved in water, aqueous solution: NaCl
(aq)
is salt water solution used after product - indicates gas
produced
: H
2 ↑
used after product - indicates solid
produced
: PbI
2 ↓
7
Symbols used in equations ■
double arrow indicates a reversible reaction (more later)
■
, heat supplied to rxn shows that
■
indicates catalyst supplied
(here, platinum is catalyst) 8
What is a catalyst?
substance that speeds up rxn, w/o being changed or used up in rxn Enzymes - biological or protein catalysts in your body 9
#3. The Skeleton Equation Uses formulas and symbols to describe rxn –but doesn’t indicate how many; means they’re NOT balanced All chem equations are
description
of rxn 10
1.
Write a skeleton equation for: Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.
2.
Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
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Now, read these equations:
Fe (s) + O 2(g)
Fe 2 O 3(s) Cu (s) + AgNO 3(aq)
Ag (s) + Cu(NO 3 ) 2(aq) NO 2(g) N 2(g) + O 2(g)
12
#4. Balanced Chemical Equations Atoms can’t be created or destroyed in an ordinary reaction: –All atoms we
start with
we must
end up with (balanced!)
balanced equation has same # of each element
on both sides
of equation 13
1) 2) 3) 4) Rules for balancing: Assemble
correct formulas
for all reactants and products, using “+” and “→” Count # of atoms of each type on both sides Balance elements
one at a time coefficients
by adding (the numbers in front) where you need more until LAST! save balancing the H and O (hint: I prefer to save O until the
very
last) Double-Check make sure balanced 14
Never
change coefficients ) subscript (only change – changing subscript (formula) describes different chemical – H 2 O different than H 2 O 2
Never
put coefficient in only in front
middle
of formula; 2 NaCl is okay, but Na 2 Cl is not.
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Practice Balancing Examples
_AgNO 3 + _Cu
_Cu(NO 3 ) 2
_Mg + _N 2
_Mg 3 N 2
_P + _O 2
_P 4 O 10
_Na + _H 2 O
_H 2
_CH 4 + _O 2
_CO 2 + _H 2 O
16
Balancing Equations 17 Balancing Chemical Reactions Mark Rosengarten – 8:21
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Section 11.2
p. 330
Types of Chemical Reactions
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
19
#1 - Combination Reactions Combine = put together 2 substances combine to make one cmpd (also called “synthesis”) Ca + O 2 SO 3 CaO + H 2 O H 2 SO 4 predict products, especially if
reactants are 2 elements
Mg + N 2 20 (symbols, charges, cross)
Complete and balance: Ca + Cl 2 Fe + O 2 Al + O 2 (assume iron (II) oxide is the product) Remember
first step
…write
correct formulas –
you can still change
subscripts
balancing!
at this point, but not while
Then balance
21 coefficients only by changing just
#1 – Combination Reactions Additional Notes: a) Some nonmetal oxides
with H 2 O
- produces acid: SO 2 + H 2 O (how “ acid rain ” forms) H 2 SO 3
react
b) Some metallic oxides
react with H 2 O
- produces base: CaO + H 2 O Ca(OH) 2 22
#2 - Decomposition Reactions decompose = fall apart
one reactant
breaks apart into 2 or more elements or cmpds NaCl Na + Cl 2 CaCO 3 CaO + CO 2 Note:
energy
(heat, sunlight, electricity, etc.) usually required 23
#2 - Decomposition Reactions predict products if binary cmpd (made of 2 elements) –It breaks apart into the elements: H 2 O HgO 24
#2 - Decomposition Reactions If cmpd has > 2 elements you must be given one of products –other product from the missing pieces NiCO 3 CO 2 + ___ H 2 CO 3 (aq) CO 2 + ___
heat
25
#3 - Single Replacement Reactions One element replaces another (new dance partner) Reactants must be
an element & cmpd
Products will be a different element 26 and different cmpd Na + KCl F 2 + LiCl K + NaCl LiF + Cl 2 (Cations switched) (Anions switched)
#3 Single Replacement Reactions Metals replace other metals (they can also replace H) K + AlN Zn + HCl Think of water as: HOH –Metals replace first H, then combines w/ hydroxide (OH).
Na + HOH 27
#3 Single Replacement Reactions can even tell
whether or not
replacement rxn will happen: single –b/c some chemicals more “active” others –More active
replaces
less active than list – p. 333 Metals Activity Series of Higher on list replaces lower 28
Higher activity Lower activity
The “Activity Series” of Metals
Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold 1) Metals can replace other metals, if they are above metal trying to replace (i.e. Zn will replace Pb) 2) Metals above H can replace H in acids.
3) Metals from Na upward can replace hydrogen in H 2 O
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The “Activity Series” of Halogens Higher Activity
Fluorine Chlorine Bromine Iodine
Lower Activity Halogens can replace other halogens in compounds, if they are above halogen they are replacing
2NaCl (s) + F 2(g)
MgCl 2(s) + Br 2(g)
2NaF (s) + Cl 2(g)
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#3 Single Replacement Reactions Practice:
Fe + CuSO
4
Pb + KCl
Al + HCl
31
#4 - Double Replacement Reactions
Two things replace each other.
–
Reactants must be two ionic
compounds
, in aqueous solution
NaOH + FeCl 3
–
positive ions change place (dance partners) NaOH + FeCl 3
Fe +3 OH + Na +1 Cl -1 = NaOH + FeCl 3
Fe( OH) 3 + Na Cl
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#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) 33
Complete and balance: assume all of the following reactions actually take place:
CaCl 2 CuCl 2 + NaOH + K 2 S
KOH + Fe(NO 3 ) 3
(NH 4 ) 2 SO 4 + BaF 2
34
How to recognize which type?
Look at the reactants : E + E = Combination C = Decomposition E + C = Single replacement C + C = Double replacement
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36 Practice Examples:
H 2 + O 2 H 2 O
Zn + H 2 SO 4 HgO
KBr + Cl 2 AgNO 3
+ NaCl
Mg(OH) 2 + H 2 SO 3
#5 – Combustion Reactions Combustion means “
add oxygen
” Normally, a cmpd composed of only C, H, (and maybe O) is reacted with oxygen – called “ burning ” Complete combustion, products are CO 2 and H 2 O If incomplete, products are CO (or possibly just C) and H 2 O 37
Combustion Reaction Examples:
C 4 H 10 + O 2
C 4 H 10 + O 2
(assume complete) (incomplete)
C 6 H 12 O 6 + O 2
(complete)
C 8 H 8 + O 2
(incomplete)
38
SUMMARY: An equation...
Describes a rxn Must be balanced (follows the Law of Conservation of Mass) only balance by changing coefficients
special symbols
to indicate physical state, catalyst or energy required, etc. 39
5 major types Reactions We can tell what type they are by looking at reactants Single Replacement happens based on the
Activity Series
Double Replacement happens if one product is: 1) a precipitate (an insoluble solid), 2) water (a molecular compound) , or 3) a gas 40
Section 11.3
p. 342 Reactions in Aqueous Solution Co(NO 3 ) 2 NiCl 2 CuSO 4 KMnO 4 K 2 Cr 2 O 7 K 2 CrO 4
41
Net Ionic Equations Many reactions occur in water- that is, in
aqueous solution
When dissolved in water, many ionic cmpds “dissociate”, or separate, into cations & anions Now write ionic equation 42
Net Ionic Equations Example (needs to be a double replacement reaction) AgNO 3 + NaCl AgCl + NaNO 3 1. this is the full balanced equation 2. next, write it as ionic equation by splitting the cmpds into their ions: Ag
1+
+ NO 3
1-
+ Na
1+
+ Cl
1-
AgCl
+ Na
1+
+ NO 3
1-
Note that the AgCl did not ionize, because it is a
“precipitate” (Table 11.3 p. 344)
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Net Ionic Equations 3.
simplify
by crossing out ions not directly involved (called spectator ions)
Ag 1+ + Cl 1-
AgCl
This is called the
net ionic equation
Let’s talk about precipitates before we do some other examples 44
Predicting the Precipitate Insoluble salt is a precipitate [note Figure 11.11, p.342 (AgCl)] General solubility rules are found: a) Table 11.3, p. 344 in textbook b) Reference section - page R54 (Table B.9) 45
Let’s do some examples together of net ionic equations, starting with these reactants:
46
BaCl
2
+ AgNO
3
→ 47
NaCl + Ba(NO
3
)
2
→ 48
Pb(NO 3 ) 2(aq) + H 2 SO 4(aq) 49