CHEMICAL REACTIONS
7.1 SKIP MOLES
True False Statement True False
Products are on the left, and yield reactants on the right of a chemical
equation
Law of conservation of mass says that matter (elements) cannot be
created or destroyed
When balancing equations you CAN change the subscripts, but NOT the
coefficients
Avogadro's number is 6.02 x 1023 which is about a mole
Cu + O2 CuOIs balanced
Chemical Reactions
Chemical reactions change substances into new substances with new chemical and physical properties
Ways to know a chemical reaction is occurring: A release of gas A color change Production of light and/or heat The production of a precipitate (solid)
Parts of Chemical Reactions
The Law of Conservation of Mass States that no matter can be created nor
destroyed in a chemical reaction
# on the left = # on the right
Two parts of a chemical reaction
Reactants: a substance or molecule that participates in a chemical reaction Usually found on the left side of an equation
Products: a substance that is formed in a chemical reaction Usually found on the right side of an equation
Parts of a chemical equation
2 H2 + O2 2 H2O
Atoms are rearranged in chemical reactions to make new substances by making or breaking bonds.
Products Reactants
Coefficient
Subscript
Chemical Equations
Chemical equation: A representation of a chemical reaction that
uses symbols to show the relationship between the reactants and products
CH4 + O2 CO2 + H2O
When balancing a chemical reaction you may add coefficients in front of the compounds to balance the reaction, but you may NOT change the subscripts.Changing the subscripts changes the
compound!! Subscripts are determined by the valence
electrons (charges for ionic or sharing for covalent)
The subscripts tell you how many atoms of a particular element are in a compound.
The coefficient tells you about the quantity, or number, of molecules of the compound
1. Write the correct formula for the reactants and the products.
2. Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side.
3. Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element
4. Check your answer to see if: The numbers of atoms on
both sides of the equation are now balanced.
The coefficients are in the lowest possible whole number ratios. (reduced)
Write the equation that describes the burning of magnesium in air to form magnesium oxide.
Magnesium + Oxygen (air) Magnesium Oxide
Mg + O2 MgO
1 Mg 1 Mg 2 O 1 O
2
2
2
Balanced!
Potassium metal reacts violently with water to produce potassium hydroxide and hydrogen gas.
Potassium + Water Potassium Hydroxide + Hydrogen Gas
Math Practice pg 195
1. Balance the production of hydrogen chloride from hydrogen and chlorine
Math Practice
Balance H2O2 H2O + O2
Mg + HCL H2 + MgCl2
Math Practice
Ethylene, C2H4 burns in the presence of oxygen to produce carbon dioxide and water vapor. Balance.
Moles
(Mol) is the amount of subatnce that contains about 6.02 x 1023 particles of that substance.
Called Avagardo’s # Usually atoms,
ions, or molecules
Molar mass- mass of 1 mole of a substance
TYPES OF REACTIONS
Ch. 7.2
True False Statement True False
A synthesis reaction is when a compound breaks down into 2 or
more elements
In single replacement 1 pair switches places, and usually has 2
compounds on both sides
Combustion reactions always yield heat, light and water
Oxidation reactions gain electrons, while reduction lose electrons
AB A + BIs decomposition
Types of reactions
5 Types of Reactions Synthesis Single Double Decomposition Combustion
Synthesis
Synthesis Reaction: A reaction in which two or more substances combine to form a new compound
A + B AB
Example: 2Na + Cl2 2NaCl
Decomposition
Decomposition Reaction: A reaction in which a single compound breaks down to form two or more simpler compounds.
AB A + B
Example: 2H2O 2H2 + O2
Single Displacement
Single-Displacement Reaction: A reaction in which one element or radical
takes the place of another element or radical in a compound
AX + B BX + A
Example: 3 CuCl2 + 2Al 2AlCl3 + 3Cu
Double Displacement
Double-Displacement Reactions: A reaction in which a gas, solid, or a
molecular compound forms from the apparent exchange of atoms or ions between two compounds
AX + BY AY + BX
Pb(NO3)2 + K2CrO4 PbCrO4 + 2 K2 NO3
Combustion
Combustion Reaction: The oxidation of an organic compound in which heat is released Also known as
“burning” Always contain a
hydrocarbon and oxygen from the air as reactants
Always produce carbon dioxide, water, and heat
CH4 + 2O2 → CO2 +
2H2O + heat
LEO says GER!!!
Electrons are sometimes transferred in chemical reactions These reactions
are called oxidation-reduction reactions (REDOX reactions)
Oxidation Substances that
lose electrons are oxidized
Reduction Substances that
accept electrons are reduced
LEO-Lose Electrons =
Oxidation
GER-Gain Electrons =
Reduction
Oxidation or Reduction?
Fe changes to Fe2+ oxidation
Pb4+ changes to Pb2+ reduction
F changes to F1- reduction
Cr2+ changes to Cr3+ oxidation
Mg2+ changes to Mg reduction
ENERGY CHANGE AND REACTION RATES
7.3/4
True False Statement True False
Endothermic releases energy/forms bonds, while exothermic absorbs
energy/breaks bonds
Increasing temperature speeds up the reaction rate
The smaller the surface area and concentration, that faster the
reaction rate
A catalyst is a substance that speeds up a reaction without being
consumed
Reaction rate, is the rate at which products turn into reactants
Energy is released or absorbed
Absorbs energy Energy is required
to break bonds
Releases energy Energy is greater
than energy needed to break bonds
Endothermic Reaction Exothermic Reaction
Conservation of Energy
Energy is not created or destroyed in endothermic and exothermic reactions
Total energy at beginning = total energy at end
Reaction Rate
Rate at which reactants change into products over time
How fast reactants are being consumed How fast the products are being formed How fast energy is absorbed or released
Factors Affecting Reaction Rate Temperature
in temp= in rate Faster particles
in temp= in rate Slower particles
Surface Area in S.A= in rate
More collisions
Factors Affecting Reaction Rate Stirring
collisions= in rate
Ex: Washing machine
Concentration # of particles in a
given volume in conc.= in rate in pressure= in
rate gases
Factors Affecting Reaction Rate
Catalyst Affects substance
w/out being used up
Speeds up reaction
Written over yield arrow
EQUILIBRIUM
Ch 7.5
True False Statement True False
Means an equation is reversible/at equilibrium
Equilibrium means the forward and reverse paths of the reaction take
place at the same rate
There are 3 types of equilibrium-chemical, physical and atomic
La Chatelier said when a change is introduced, the equation will do the
opposite
Temperature, pressure, and concentration affect equilibrium
Equilibrium
State in which the forward and reverse paths of change take place at the same rate Physical and Chemical
Types of Equilibrium
Opposing physical change takes place at the same time
Opposing chemical changes take place at the same time
Physical Chemical
La Chatelier’s Principle
When a change is introduced to a system in equilibrium, the equilibrium shifts in the direction that relieves the change
Factors Affecting Equilibrium Temperature
in temp will shift in the direction that removes heat from the system
Pressure in pressure will
shift in the direction that decreases the pressure of the system
Factors Affecting Equilibrium Concentration
Equilibrium will shift in direction that produces concentration