Download RXN-4-STUDENTS - Rothschild Science

BALANCING EQUATIONS &
CHEMICAL REACTIONS
Evidence of Chemical Change





Changes in Energy (E)
Release of E as heat
Release of E as light
Production of sound
Reduction or increase of
temperature
Absorption or release of
electrical Energy




Formation of new
substances
Formation of a gas
Formation of a
precipitate
Change in color
Change in odor
Conservation of Mass
Law of Conservation of Mass
 In any physical or chemical reaction, mass
is neither created nor destroyed; it is
conserved!
Reactants
Products
Same number of atoms on both
sides of the equation!
Balancing Equations
In every balanced equation
each side of the equation
has the same number of atoms
of each element
Vocab Terms
 Subscripts – tells how many atoms of each
element you have NH3 (one nitrogen, three
hydrogen)- DON’T mess with these!!
 Coefficients – small whole number that appears
in front of a chemical formula in an equation –
you get to “mess” with these. 2NH3 (Two
molecules of ammonia or two moles of ammonia)
  the arrow means yields or reacts to produce
REACTANTS
PRODUCTS
You have to get the same number of elements
on each side of the reaction
Balancing Rules
1.
2.
3.
4.
Never touch subscripts when balancing
equations, you will change the substance
Include all sources of the element
CH3CHOOH + NaOH
Polyatomic ions that appear intact on both
sides of the equation, can be balanced as a
group (PO4)
Coefficients in your balanced equation contain
the lowest possible ratio.
Balancing!
Aluminum + Oxygen  Aluminum Oxide
Al + O2  Al2O3
Until you get good at this, it is helpful
to write the number of atoms of each element on
both sides of the equation. It helps you to keep
track of the atoms.
Balancing!
Ethene + Oxygen  Carbon Dioxide + water
C2H4 + O2  CO2 + H2O
Balancing!
Hydrogen gas + nitrogen gas  ammonia
Remember your diatomic molecules!!!
Try this one!
NaNO3 + CrCl3  NaCl + Cr(NO3)3
Balance this equation…
NaNO3 + CrCl3  NaCl + Cr(NO3)3
Write the word equation.
Important stuff!
Four abbreviations are
used to indicate
physical states of
chemicals: shown as
subscripts in the chemical
equation
(s) = solid
(l) = liquid
(g) = gas
(aq)= aqueous solution
(dissolved in water)
Symbols over the arrow
indicate the conditions of
the reaction
Heat
Pressure
Temperature
Catalyst
Reversible reaction
Why does it happen?
Use the file to make four hash marks
perpendicular to the face of the penny.
Carefully drop the penny into the 6M HCl
solution.
Check out the Pennys!
Make some qualitative observations about the
pennies. (Look at the dates- remember what
you learned at the beginning of the year in the
Penny Density Lab)
As we proceed: You may want to write these down!
1. What kind of reaction
2. Write and balance the chemical equation.
3. Explain your observations.
4. What kind of quantitative observations would be
helpful?
Warm UpA sample contains a compound with 3.60 g of
carbon and 0.61 g of hydrogen. The molar
mass of the compound is 42.09g/mol.
Determine the formula of the compound.
Remind me to pass back your EMP Formula
Packets. I only graded a few- answers are
posted on line.
Wonder Projects- HONORS
ONLY
Go to my website
REACTIONS
Combination Reaction
or Synthesis Reaction
 Two or more simple substances react to
form a more complicated one
A + B  AB
Fe + S  FeS
Combination Reactions
We can predict the products of ionic compounds by
thinking about the charge!
Ga (s) +
O2 (g) 
Cu (s) +
S(s)

Are there 2 possible products to the 2nd reaction?
How would we “say” these equations?
Decomposition Reaction
 A decomposition reaction is the opposite
of a composition reaction - a complex
molecule breaks down to make simpler
ones.
AB  A + B
2 H2O  2 H2 + O2
Decomposition Reactions
Harder to predict the products…always remember
your diatomics.
Water is often a product!
HgO(s) 
NH4NO3
CaCO3 
(Carbonates usually decompose to CO2)
Decomposition Reactions
HgO(s)
2HgO(s)


2Hg(l)
+
O2 (g)
NH4NO3
NH4NO3


N2O
+
2H2O
CaCO3

CaO
+ CO2
The only way to really know is to do the
reaction!!
Warm Up
Predict the products of the following reactions.
1.H2O2

1.Mg + N 
Warm Up
Predict the products of the following reactions.
1.H2O2

We heat the dihydrogen dioxide and the
vapor turns out to be water…
2. Mg + N 
Mg3N2
How are you doing on the Word
Equation WS?
Single Replacement
 This is when one element trades places with
another element in a compound.
A + BC  AC + B
Mg + 2H2O 
Single Replacement Reactions
Easy to predict the products. Look at the ions…
remember that a cation has to bond to an anion!!
Don’t forget about diatomics!
Zn(s) +
H2SO4(aq) 
Na(s) +
H2O 
OOPS! Did we balance them?
Single Replacement Reactions

 ZnSO4(aq)
Zn(s) +
Zn(s) +
H2SO4(aq)
H2SO4(aq)
Na(s) +
Na(s) +
2Na(s)+
H2O 
H+OH-(l) 
2H+OH-(l)  2NaOH
+ H2(g)
+ H2(g)
Single Replacement Reactions
Reactivity of a metal makes a difference!
If a metal is more reactive than the metal it is
displacing a rxn will occur. If the metal is
less reactive than the metal it is
displacing, a rxn will not occur.
Metal Reactivity
Increases down a group
Decreases across a period
Brainiacs-- Metal Reactivity
Reactivity in Single Displacement
Cs
Na
KMnO4  CsMnO4
Will this occur??
+
+
+
K
KMnO4  NaMnO4 + K
Will this occur?
Double Replacement Reaction
 This is when the anions and cations of two
different molecules switch places, forming
two entirely different compounds
AB + CD  AD + CB
Pb(NO3)2 + 2KI  PbI2 + 2KNO3
Double Replacement Reactions
Two ionic compounds in aqueous solution
Generally 3 things happen:
1.
A precipitate (solid) occurs
Pb(NO3)2 + 2KI  PbI2 + 2KNO3
Double Replacement Reactions
2.
One product is a gas that bubbles out of
the mixture
2NaCN(aq) + H2SO4  2HCN(g) + Na2 SO4(aq)
Double Replacement Reactions
3.
One product is a molecule while the
other products remain ions
Ca(OH)2(aq) + 2HCl(aq)  Ca+2 + Cl- + 2 H2O(l)
Warm Up- Determine the type of
reaction and predict the products.
1.Al + Br2

2.FeO + Na 
3.SnCl4 
4.NaNO3 + CaCO3 
Combustion Reactions
 A combustion reaction is when oxygen
combines with another compound or
element producing energy.
 When hydrocarbons (C?H?) combust,
water, carbon dioxide and energy are
produced.
C10H8 + O2  CO2 + H2O + Energy
Can you balance it?
Combustion of Naphthalene
Combustion Reactions
Combustion of propane:
C3H8 +
O2

Combustion of methane:
CH4 +
O2

Combustion of butene (this one is tricky!)
C4H6 +
O2

Teacher Demo Extraordinaire!
What is a flame video- Science Friday
http://www.sciencefriday.com/video/06/08/2012/
what-is-a-flame.html
Combustion Analysis Problems…
Honors Only
So, we can collect the water vapor and the
carbon dioxide…. do some calculations…. and
determine the empirical formula of the
hydrocarbon.
C?H?
+
O2 
CO2 +
11.56g
H2O
2.36g
Start the Types of Reactions Lab
1. Spend about 5 minutes on the Background.
2. Read through the procedure at each station.
3. You need to get at least 3 of the 6 stations
finished today.
4. Goggles must be worn at all times.
5. Listen carefully for safety concerns while I
intro the labs.
Predict the products, balance and classify
the following reactions.
Li + MgCl2 
C6H12 + O2 
Ca(NO3)2 + NaOH 
Warm Up- Friday
Balance the following equations:
C3H6 +
O2 
CO2 + H2O
C7H14 +
O2 
CO2 + H2O
Finish Types of Rxns Lab
What do the equations mean?
The coefficients indicate the number of moles of
the reactants necessary… to form a certain
mole of the product.
Mole to Mole Ratio
3K + AlCl3  Al + 3KCl