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CHEM120 Lecture Notes - Stoichiometry, Reagent, Molar Concentration

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Carey Bissonnette

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Chemical Reactions
Chemical Reactions and Chemical Equations:
Types of physical evidence to look for:
A colour change
Formation of a solid (precipitate) within a clear solution
Evolution of a gas
Evolution or absorption of heat
The coefficients required to balance a chemical equations are called stoichiometric coefficients.
If an element occurs in only one compound on each side of the equation, try balancing this
element first
When one of the reactants or products exists as the free element, balance this element last
In some reactions, certain groups of atoms remain unchanged. In such cases, balance these
groups as a unit.
It is permissible to use fractional as well as integral numbers as coefficients. At times, an equation
can be balanced most easily by using one or more fractional coefficients and then, if desired,
clearing the fractions by multiplying all coefficients by a common multiplier.
The combustion of hydrocarbons and of carbon-hydrogen-oxygen compounds produces carbon dioxide
and water as the only products.
The Greek capital letter delta, Δ, means that a high temperature is required.
A catalyst is a substance that enters into a reaction in such a way that it speeds up the reaction without
itself being consumed or changed by the reaction.
A stoichiometric factor relates the amounts, on a mole basis, of any two substances involved in a
chemical reaction; thus a stoichiometric factor is a mole ratio.
Chemical Reactions in Solution:
Concentration of the solution.
Molarity = amount of solute (in moles) / volume of solution (in litres)
M = n/V
n = M x V
Solution Dilution:
When a volume of a solution is diluted, the amount of solute remains constant.
Determining the Limiting Reactant:
The limiting reactant determines the quantities of products formed.
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