Transcript Chemical Equations and Reactions

Chemical Equations and
Reactions
By: Ms. Buroker
Writing Chemical Reactions
• In order to be able to write a chemical
reaction, you MUST know how to write
formulas from names!
• If you still cannot do this…you are going to
have MAJOR trouble
Chemical Reaction
Chemical Reaction – process by which the
• _______________
atoms of one or more substance are
rearranged to form different substances
• A chemical reaction is also called a
Chemical Change
_______________
Indications of a chemical reaction
• Evolution of energy as heat or light
• Production of a gas
• Formation of a precipitate= a solid that is
produced as a result of chemical reaction.
• Color Change
• A Change in Odor
Writing Chemical Equations
• A substance that undergoes a reaction is called a
_______________
.
reactant
– Reactants are written on the left of the arrow
– These will be the things you start with
• When reactants undergo a chemical change, each
new substance formed is called a
_______________
.
product
– Products are written on the right of the arrow
– These are the things that you produce
Reactants  Products
Writing Chemical Equations
reactants
• _______________–
starting chemicals
products
• _______________–
substances that are
formed
• + separates substances (usually read as
“and”)
•  separates reactants from products
(usually read as gives, produces, or yields)
• Ex: Reactant 1 + Reactant 2  Product 1 + Product 2
Writing Chemical Equations
•
•
•
•
We typically want to represent the state of
matter each of the reactants and products are
in during the reaction.
solid
(s) – _______________
liquid
(l) – _______________
gas
(g) – _______________
aqueous
(aq) – _______________
Dissolved in water
Word Equations
• The simplest way to represent a reaction is
by using words to describe all the reactants
and products, with an arrow placed
between them to represent change.
• Example:
Solid iron and chlorine gas react to produce solid
iron (III) chloride
Skeleton Equations
• Word equations can be converted into skeleton
equations by substituting chemical formulas for the
names of compounds and elements.
• In order to be successful, you’ll need to memorize
the following:
There are 7 elements that
occur as diatomic molecules:
H,N,O,F,Cl,Br,I
• This means, they occur in pairs … such as H2, or O2
instead of just H or O
Skeleton Equations
• Try the word equation we just looked at
• Solid iron and chlorine gas react to produce solid iron
(III) chloride
Fe (s) + Cl2 (g)  FeCl3 (s)
Remember … the 7
diatomic elements:
H, N,O,F,
Cl,Br,I
Try this example…
• Write the skeleton equation for solid
magnesium reacting with oxygen gas to give
solid magnesium oxide
Mg (s) + O2 (g)  MgO (s)
Remember … the 7
diatomic elements:
H, N,
O,F,Cl,Br,I
Try this example…
• Write the skeleton equation for solid carbon
reacting with solid sulfur to produce liquid
carbon disulfide
C (s) + S (s)  CS2 (l)
Try this example…
• Write the skeleton equation for solid calcium
reacting with chlorine gas to produce solid
calcium chloride
Ca (s) + Cl2 (g)  CaCl2 (s)
Remember … the 7
diatomic elements:
H, N,O,F,
Cl,Br,I
Skeleton Equation vs. Chemical
Equation
• In a chemical equation the Law of
conservation of matter MUST be observed!
**Matter cannot be created or destroyed**
• For us, this means the # of atoms of reactants
= the # of atoms of products
• What you start with has to equal what you
end with
Definitions
subscripts
• _______________–
the numbers at the bottom of a
chemical formula. They apply only to the atom to
which they are attached.
• CaCl2…H2O…Na3PO4
• Subscripts CANNOT be changed
coefficients
• _______________–
these will be the numbers that
you will put in front of the chemical formulas. They
will be multiplied to the compounds they are in front
of.
• Coefficients CAN be changed
Balancing Chemical Equations
Balanced chemical equations contain the same number
of each kind of atom on each side of the arrow.
Steps:
1. Write the unbalanced equation.
2. Inventory the atoms in the reactants and in the products.
3. Balance the equation.
Strategies:
• Balance elements left-to-right on the Periodic Table
(metals first, then nonmetals)
• Leave H and O until last.
Let’s Do Some Examples
1. Write the unbalanced equation.
__Zn (s) + __HCl (aq) → __ZnCl2 (aq) + __ H2 (g)
2. Inventory reactants and products.
__Zn (s) + __HCl (aq) → __ZnCl2 (aq) + __ H2 (g)
Zn
1
Zn
1
Cl
1
Cl
2
H
1
H
2
3. Balance the equation (by changing
coefficients.)
__Zn (s) + 2
__HCl (aq) → __ZnCl2 (aq) + __ H2 (g)
Zn
Zn 1
1
Cl
1 2
H
1 2
BALANCED !
Cl 2
H 2
BALANCED !
Try to balance this reaction:
__CH4 (g) + __O
2 2 (g)  __CO2 (g) + __H
2 2O (l)
C
1
C 1
H
4
H 2 4
O
24
O 3 4
Try to balance this reaction:
3
__KClO

__KCl
+
__O
2
2
(s)
3 (s)
2 (g)
K 1 2
K 1 2
Cl 1 2
Cl 1 2
O 3 6
O 2
6
Try to balance this reaction:
__Al(OH)
2
3 2SO4(aq)  __Al2(SO4)3(aq) + __H
6 2O(l)
3(s) + __H
Al 1 2
Al 2
S
S
1 3
3
H 5 8 12
H 2 12
O 7 10 18
O 13 18
Balance these equations
•
•
•
•
•
•
•
•
__ Mg + __ O2 → __ MgO
__ Ca(ClO3)2 → __ CaCl2 + __ O2
__ Cu + __ AgNO3→ __ Cu(NO3)2 + __ Ag
__KOH + __ H3PO4 → __ K3PO4 + __ H2O
2 Mg + O2 → 2 MgO
Ca(ClO3)2 → CaCl2 + 3 O2
Cu + 2 AgNO3→ Cu(NO3)2 + 2 Ag
3 KOH + H3PO4 → K3PO4 + 3 H2O
Examples
Write the balanced chemical equation for the following
reactions:
1.) hydrogen gas and chlorine gas react to give hydrochloric acid
which is aqueous in solution
2.) aqueous sodium hydroxide and aqueous calcium bromide
react to give solid calcium hydroxide and aqueous sodium
bromide
3.) aqueous potassium iodide react with aqueous lead (II) nitrate
to form aqueous potassium nitrate and solid lead (II) iodide
Types of Chemical Reactions
•
•
•
•
•
Synthesis Reaction
Decomposition Reaction
Single Displacement Reaction
Double Displacement Reaction
Combustion
The Synthesis Reaction
A + X  AX
– Two or more substances combine to form a new compound
Common types you should know:
1.) most metals plus oxygen will react to form oxides of the
element + oxygen  metaloxide
4Na(s) + O2(g)  2Na2O(s)
2.) most metals plus halogens will give salts of the metal + halogen
Mg(s) + Cl2(g)  MgCl2(s)
3.) active metal oxides plus water will make a base  metal + OHMgO(s) + H2O(l)  Mg(OH)2(aq)
The Decomposition Reaction
AX  A + X
*A compound that breaks down into two or more
substances
Common Types you should know:
1.) metal carbonates break down into the metal oxide and carbon
dioxide gas
CaCO3 (s)  CaO + CO2(g)
2.) metal hydroxides break down into metal oxides and water  the
reverse of the composition or synthesis
Mg(OH)2(s)  MgO(s) + H2O(l)
Decomposition Continued
3.) metal chlorates break down into metal chlorides
and oxygen gas
2KClO3(s) 2KCl(s) + 3O2(g)
Let’s Practice a Little …
• Predict the products. Write and balance the
following synthesis reaction equations.
• Sodium metal reacts with chlorine gas
2 Na(s) + Cl2(g)  2 NaCl(s)
• Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g)  MgF2(s)
• Aluminum metal reacts with fluorine gas
2 Al(s) + 3F2(g)  2 AlF3(s)
Let’s Practice a Little …
Predict the products. Write and balance the
following decompostion reaction equations.
• BaCO3(s)  BaO(s) + CO2(g)
• PbO2(s)  Pb(s) + O2(g)
•2NaClO3(s)  2 NaCl(s) + 3 O2(g)
Single Replacement
•
Single Replacement
___________________–
Reaction
when the atoms of
one element replace the atoms of another
element in a compound
• Of the form :
A + BX  AX + B
• For example:
Cu + 2AgNO3  2 Ag + Cu(NO3)2
Metals will
replace metals
and non
metals will
replace non
metals
Single Replacement Reactions
• In order for a single replacement reaction to occur,
the element that is ____________
must be strong
alone
enough to push the other element out of the way.
• The activity series show you the relative strength of
the elements.
• In order for the reaction to occur, the lone element
must be above the element in the compound
• Otherwise…NO REACTION  NR
Activity Series
Will these reactions occur?
• Will the following reaction occur? If so,
complete and balance the reaction.
• Ag
+ Cu(NO3)2 
Will these reactions occur?
• Will the following reaction occur? If so,
complete and balance the reaction.
• Mg + AlCl3 
Will these reactions occur?
• Will the following reaction occur? If so,
complete and balance the reaction.
• Br2 + MgCl2 
Double Displacement (Metathesis)
• A reaction involving the exchange of ions
between 2 compounds
AX + BY  AY + BX
• Example:
– Pb(NO3)2 + 2KI 
Double Displacement (Metathesis)
AX + BY  AY + BX
Steps:
1.) Write the cations on the other side of the arrow.
2.) Switch the anions
3.) Check to make sure the compounds are written
correctly (“check charges”)
4.) Balance the reaction with coefficients
Mixed Practice
• State the type, predict the products, and
balance the following reactions:
1. BaCl2 + H2SO4 
2. C6H12 + O2 
3. Zn + CuSO4 
4. Cs + Br2 
5. FeCO3 
Example
• Sodium chloride reacts with silver nitrate
Example
• Hydrochloric acid reacts with calcium
hydroxide
Combustion
• when O2 combines with a hydrocarbon to
form CO2 and H2O
CxHy + O2  CO2 + H2O
• For example:
– CH4 + 2 O2  CO2 + 2H2O
– 2CH3OH + 3O2  2CO2 + 4H2O
Three things drive a double displacement
• The formation of a solid
To determine if a solid forms, we take a look at how the
reactants go into the reaction and what products they form.
To do this we need solubility rules- these tell us whether or
not something will dissolve in water and thus form a
solution, or will it will precipitate out.
• The formation of a gas
• The formation of a liquid
Reactions where water is formed fall into this category …
they are known as neutralization reactions. When acids
and bases react together- they neutralize each other by
forming an acid and a salt.
Equations
• Molecular Equations – show the complete
chemical formulas. Does not indicate ionic
character
• Total Ionic Equations– shows all ions. Actually
how the particles exist in the solution
• Net Ionic Equations- represents what was
involved in making the product.
Steps for Writing Ionic Equations
1. Write the balances molecular equation
(balanced chemical equation)
2. Break every thing down into its ions EXCEPT
the solid, gas, or water (complete ionic
equation)
3. Cross out everything that is the same (in the
same state) on both sides (spectator ions)
4. Write what is left (net ionic equation)
Solubilities Not on the Table!
• Gases only slightly dissolve in water
• Strong acids and bases dissolve in water
– Hydrochloric, Hydrobromic, Hydroiodic, Nitric, Sulfuric,
Perchloric Acids
– Group I hydroxides (should be on your chart anyway)
Total Ionic Equations
Molecular Equation:
K2CrO4 + Pb(NO3)2 
PbCrO4 + 2 KNO3
Soluble
Insoluble
Soluble
Soluble
Total Ionic Equation:
2 K+ + CrO4 -2 + Pb+2 + 2 NO3- 
PbCrO4 (s) + 2 K+ + 2 NO3-
Net Ionic Equations
• These are the same as total ionic equations,
but you should cancel out ions that appear on
BOTH sides of the equation
Total Ionic Equation:
2 K+ + CrO4 -2 + Pb+2 + 2 NO3- 
PbCrO4 (s) + 2 K+ + 2 NO3Net Ionic Equation:
CrO4 -2 + Pb+2  PbCrO4 (s)
Example
• Write the balanced chemical equation, the
complete ionic equation, and the net ionic
equation for:
• lead (II) nitrate and potassium iodide. Solid
potassium iodide will be formed.
Net Ionic Equations
• Try this one! Write the molecular, total ionic, and net ionic
equations for this reaction: Silver nitrate reacts with Lead
(II) Chloride in hot water.
Another Example
• Write the balanced chemical equation,
complete ionic equation, and net ionic
equation for:
• calcium chloride and sodium carbonate. Solid
calcium carbonate will be formed.
The Formation of a Liquid: Steps
First, you must identify that the compounds are an
acid and a base …
1.) Acids have a H in front … HCl, HNO3, etc
2.) Bases have OH on their end … NaOH, Ca(OH)2
Secondly, you complete the reaction with the salt
and water.