Balanced Chemical Equation – a representation of a chemical reaction using symbols that show the same number of atoms of each element on both sides of the reaction arrow

Coefficients – whole numbers written in front of a chemical symbol to represent the number of moles of that substance

Reactants – the chemical substances that are present before a chemical reaction starts; typically written on the left side of the arrow

Products - the chemical substances that are present after a chemical reaction occurs; typically written on the right side of the arrow

Subscripts – the whole numbers written to right and below the symbol for that element indicating how many atoms of that substance are present in the substance

Release of a gas Evidence - Bubbles

Change in temperature Evidence – Temperature goes up (exothermic) Evidence – Temperature goes down (endothermic)

Change in color Evidence - solution changes color

Formation of a precipitate Evidence - forms and settles to the bottom

Energy is released Evidence - light or sound

Symbol Meaning of Symbol

(s) A reactant or product in the solid state; also used to indicate a precipitate

(l) A reactant or product in the liquid state

(g) A reactant or product in the gaseous state

(aq) A reactant or product in an aqueous solution (dissolved in water)

→ Used to indicate the direction of a reaction. Translated as “yields” of “produces”.

Synthesis

Decomposition

Single Replacement

Double Replacement

Combustion

Generic Form: A + B → AB

Reactants:A and B are either elements or simple compounds

Products:AB is a complex compound formed from A and B

All Synthesis Reactions involving uncombined elements are REDOX Reactions

Reaction Mechanism:The atoms of A and B are bonded together to form a

single new compound

2 Na + Cl2 → 2 NaCl› Sodium atoms and chlorine gas molecules

combine to form a single new product› Sodium chloride is the product of the reaction

2 Mg + O2 → 2 MgO› Magnesium atoms and oxygen gas molecules

combine to form a single new product› Magnesium oxide is the product of the reaction› In a moment, we will also see that this

reaction can also be classified as a combustion reaction

Generic Form: AB → A + B

Reactants:AB is a complex compound formed from A and B

Products:A and B are either elements or simple compounds

All Decomposition Reactions involving uncombined elements are REDOX Reactions

Reaction Mechanism:The compound AB breaks down into its elements or into

simple compounds

2 H2O2 → 2 H2O + O2

› Hydrogen peroxide molecules break down to form new products that are simple molecules

› Water and oxygen gas are the products of the reaction

2 KClO3 → 2 KCl + 3 O2

› Potassium chlorate molecules break down when heated to form new products that are simple molecules

› Potassium chloride and oxygen gas are the products of the reaction

Generic Form: A + O2 → H2O + CO2

Reactants:A is a hydrocarbon (a compound of hydrogen and carbon)O2 is oxygen gas (we will assume more than enough oxygen is

present)

Products: When combusting a hydrocarbon, the products will

always be water and carbon dioxide

All Combustion Reactions are REDOX Reactions

Reaction Mechanism:The hydrocarbon is oxidized and produces energyWith a hydrocarbon the reaction is generally rapid

C2H4 + 3 O2 → 2 CO2 + 2 H2O

› Ethene (also known as acetylene) is a hydrocarbon

› When O2 is a reactant, the reaction must be combustion

› The products must be water and carbon dioxide

Generic Form: A + BY → AY + B

Reactants: A is a metal elementBY is an ionic compound

  Products:

AY is an ionic compoundB is a metal element or a diatomic molecule

All Single Replacement reactions are REDOX & Precipitation Reactions

Reaction Mechanism:A and B are elements of the same type If A is more reactive than B, the reaction occurs with A replacing B If A is less reactive than B, no reaction can occur

2 Al(s) + 3 CuCl2(aq) → 2 AlCl3(aq) + 3 Cu(s)Aluminum is a metal and copper is the metal in the

ionic compoundAluminum is more reactive than copper, therefore

the reaction occursThe aluminum replaces the copper ion in the ionic

compound and the element copper forms as a precipitate

What happens if the reaction is reversed?Cu(s) + AlCl3(aq) → No reaction occursThe copper is not more reactive than the aluminum,

so no reaction occurs

Generic Form: AX + BY → AY + BX

Reactants: AX is an ionic compound BY is an ionic compound

  Products:

AY is an ionic compound BX is a an ionic compound

All Double Replacement reactions are Precipitation Reactions, but none are REDOX Reactions

Reaction Mechanism: A and B are elements of the same type (both are metals ) as are X and Y

(both are non-metals) A replaces B and X replaces Y (the ions trade partners) If an insoluble product (precipitate or insoluble gas) is produced, the

reaction occurs

Na2SO4(aq) + Ba(NO3)2(aq) → 2 NaNO3 (aq) + BaSO4(s)The ions in the two ionic compounds change partners

and form two new ionic compoundsBaSO4 is not soluble in waterBaSO4 is the product of the reaction

What happens if there is no precipitate?Na2SO4(aq) + KNO3 (aq) → No Reaction

The ions of sodium, potassium, sulfate, and nitrate cannot produce an insoluble product

Therefore, there is no product of the reaction and that means there is no reaction between the sodium sulfate and the potassium nitrate

Reduction-Oxidation (REDOX) Reactions› Electrons migrate resulting in a change in

oxidation numbers

Precipitation› A solid product is produced as a result of

the reaction

Strong Acid-Base Neutralization› Reactions produce water & a salt

TYPE REDOX(migration of

electrons)

PRECIPITATION(solid product

formed)

ACID-BASE NEUTRALIZATI

ON

SynthesisWhen an

uncombined element is

present

Only when two gases combine to

form a solidNever

Decomposition When an uncombined element is

present

Never Never

Combustion Always Never Never

Single Replacement

Always When metal replaces metal

Never

Double Replacement

Never Always(Special Case: gas

is produced)

When reactants are acids &

bases

• Mass cannot be created or destroyed in chemical reactions

• Matter can be and is changed by the rearrangement of atoms, but the mass cannot change

• Therefore, the same atoms of matter still exist after a chemical reaction as were present before the reaction

Equations describe chemical reactions showing the reactants and products

Since mass must be conserved, the same number of atoms of each element must be present in the products as were in the reactants

Individual atoms do not react alone – many atoms react at the same time

Atoms are counted using moles

The number of moles of each reactant and product must be adjusted to have the same number of atoms on both sides of the reaction

That process is known as balancing the reaction

It is a process of counting atoms

The chemical formula of the compounds or elements cannot be changed – you may not change anything about the reactants or the products themselves

Only the coefficients (the number of moles) can be changed

Changing the number of moles (coefficients), changes the number of atoms of every element in the compound

Coefficients (moles) are changed until the same number of each atom are on both sides of the reaction

List the elements involved in the reaction

Count the number of moles of each element on both sides of the reaction

Adjust the number of moles using coefficients so that the first element is balanced

Recount the number of moles of each element

Repeat the process until the same number of moles is present for every element in the reaction

Check the result to make sure that the balanced reaction is the lowest whole number ratio of the reactants and products