Download Catalyst Activity (in your notebook)

Chemical Reactions and
Equations
Chemical Reactions
• when a substance
changes identity
– reactants- original
– products- resulting
• law of conservation of
mass
– total mass of reactants = total
mass of products
Chemical Reactions
• chemical equation
– represents identities and relative amounts of
reactants and products in the chemical reaction
– uses symbols and formulas
Signs of Chemical Reaction
• heat or light
– can also happen with physical
changes
• gas bubbles
– means a gas is being created as
product
• precipitate
– solid is being created
• color change
Equations cannot tell us:
• if the reaction will actually occur
– depends on many factors affecting energy
• the speed of the reaction
– depends on chemical kinetics
– can be very slow, almost unnoticeably
• how the bonding actually changes
– formula may not clearly show bonding
Word Equations
• uses names instead of formulas
• helps you to write formula equation
Symbols Used in Equations
yields
reversible
above arrow:
or heat heated
MnO2 or Pt catalyst
25°C
specific T
requirement
2 atm
specific P
requirement
after a formula:
(s)
solid
(l)
liquid
(aq) aqueous:
dissolved in
water
(g)
gas
Example
• Description:
Solid sodium oxide is added to water at room
temperature and forms sodium hydroxide.
• Word Equation:
sodium oxide + water  sodium hydroxide
• Formula Equation:
Na2O + H2O  NaOH
Writing Chemical Equations
• most pure elements
– written as elemental symbol
• diatomic molecules
– molecule containing only 2 atoms
– some elements normally exist this way
– H2, O2, N2, F2, Cl2, Br2, I2, At2
• other exceptions
– sulfur: S8
– phosphorus: P4
Writing Equations
•
•
•
•
Write Word equations to show reactants and
products.
Be sure to include symbols showing states of
each reactant and product
Be sure to write the correct formula for each
(crossing over for ionic compounds!)
Balancing the equation when you are
finished.
Coefficients
• whole numbers in front of formula
• distributes to numbers of atoms in formula
• specifies the relative number of moles and
molecules involved in the reaction
• used to balance the equation
Balancing Equations
•
1.
2.
3.
4.
5.
6.
ONLY add/change coefficients- NEVER
subscripts!!!
balance one type of atom at a time
balance polyatomic ions first
balance atoms that appear only once second
balance H and O last
simplify if you can
Check at end!
Example 1
• Description:
Zinc metal is added to hydrochloric acid to
create zinc chloride and hydrogen gas.
• Word Equation:
zinc + hydrochloric acid 
zinc chloride + hydrogen
Example 2
• Solid calcium metal reacts with water to form
aqueous calcium hydroxide and hydrogen gas.
• calcium + water 
calcium hydroxide + hydrogen
• Ca(s) + H2O(l)  Ca(OH)2(aq) + H2(g)
• Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g)
Example 3
• solid zinc metal reacts with aqueous copper
(II) sulfate to produce solid copper metal and
aqueous zinc sulfate
• zinc + copper (II) sulfate 
copper + zinc sulfate
• Zn(s) + CuSO4(aq)  Cu(s) + ZnSO4(aq)
• Zn(s) + CuSO4(aq)  Cu(s) + ZnSO4(aq)
Example 4
• Hydrogen peroxide in an aqueous
solution decomposes to produce
oxygen and water
• hydrogen peroxide  oxygen +
water
• H2O2(aq)  O2(g) + H2O(l)
• 2H2O2(aq)  O2(g) + 2H2O(l)
Example 5
• Solid copper metal reacts with aqueous silver
nitrate to produce solid silver metal and
aqueous copper (II) nitrate
• copper + silver nitrate 
silver + copper (II) nitrate
• Cu(s) + AgNO3(aq)  Ag(s) + Cu(NO3)2(aq)
• Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq)
Example 6
• Carbon dioxide gas is bubbled through water
containing solid barium carbonate, creating aqueous
barium bicarbonate
• carbon dioxide + water + barium carbonate 
barium bicarbonate
• CO2(g) + H2O(l) + BaCO3(s)  Ba(HCO3)2(aq)
• CO2(g) + H2O(l) + BaCO3(s)  Ba(HCO3)2(aq)