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Stoichiometric Relationships, Definition, Purpose - Coggle Diagram
Stoichiometric Relationships
Stoichiometry
Importance
Enables chemists to determine amount of resources that should react together and predict how much product should be obtained
Chemical Equations
Shows overall change of reactants to products in a chemical reaction
Chemical Reaction
A process in which one or more substances (reactants) are converted into one or more different substances (products) by rearranging constituent atoms of the reactants
Indicators
Light or heat emission
Precipitate formation
Emission of odor
Gas formation
Color change
Types
Synthesis/Combination
Occurs when ≥ 2 simple substances combine to produce a more complex substance
General Formula: A + B –> AB
Example: H+ + OH- –> H2O
Decomposition
Occurs when a complex substance breaks down into ≥ 2 simpler substances
General Formula: AB –> A + B
Example: NH4NO3 –> NO2 + 2(H2O)
Single Displacement
Occurs when a metal displaces another metal, or when a non-metal replaces another non-metal in a compound
General Formula: A + BC –> AC + B
Zn + CuCl2 –> Cu + ZnCl2
Double Displacement
Occurs when components of 2 compounds swap places, otherwise known as "swapping of partners"
General Formula: AB + CD –> AD + CB
Example: 2(NaBr) + BaCl2 –> 2(NaCl) + BaBr2
Combustion
The reaction of a hydrocarbon with oxygen to produce carbon dioxide and water
General Formula: CaHbOc + O2 –> CO2 + H2O
Example; CH4 + 2(O2) –> CO2 + 2(H2O)
Relevant Unit Conversion
Meters
km (kilometer) = 10^3 meters
dm (decimeter) = 10^-1 meters
cm (centimeter) = 10^-2 meters
mm (millimeter) = 10^-3 meters
μm (micrometer) = 10^-6 meters
nm (nanometer) = 10^-9 meters
Mm (megameter) = 10^6 meters
Mole (Avogadro's Number)
Shortened to mol
Equal to 6.02*10^23 particles, whether these particles refer to atoms, ions, compounds, formula units, etc.
N = n x (6.02 x 10^23)
N represents the number of particles
n represents the number of moles
Mass
m = n x M
m is the mass in g
M is the molar mass in g mol^-1
General Strategy
Convert from mass to moles
Use molar ratios inn the balanced ratio in the chemical equation
Convert back to mass from moles
Relative Masses
Relative Atomic Mass (Ar)
The mass of an atom relative to the Carbon-12 isotope, which has a value of 12.000
Average mass per atom of an element
–––––––––––––––––––––––––––––– x 12
Mass of an atom of Carbon-12
Relative Isotopic Mass
Similar to Relative Atomic Mass, but uses the mass of an isotope instead
Relative Molecular Mass
Similar to Relative Atomic Mass, but uses the mass of a molecule instead
Relative Formula Mass
Similar to Relative Atomic Mass, but is used for any formula of a species or ion
m = n x M
m is the mass in g
M is the molar mass in g mol^-1
Formula
Empirical Formula
Definition
Simplest whole number ratio of atoms of different elements in the compound
Determining Process (given percentage mass)
Assume we have a 100 gram sample
Change % into grams
Convert grams to moles for each element
Write number of moles as a subscript in a chemical formula
Divide every number by the smallest number
Multiply result to get rid of fractions
Molecular Formula
Definition
Actual number of atoms of elements
covalently bonded
in a molecule
Determining Process (given Empirical Formula)
Divide the given mass by the molar mass of the compound then multiply the whole number result to the subscripts from the empirical formula
Combustion Analysis
General Formula: CaHbOc + O2 –> CO2 + H2O
Determining Process
Convert mass of each compound to mass of carbon and hydrogen
Subtract the masses of carbon and hydrogen from the given mass of CaHbOc to get the mass of oxygen in the original sample (CaHbOc)
Convert mass of oxygen to number of moles, then divide number of moles by the smallest number
Limiting Reactant
Definition
Reactant that is completely used up in the reaction, and other reactants, which are in excess, will not be fully used up
Determining Process
Write the balanced equation and focus on the molar ratio of the reactants
Convert given masses of reactants to moles
Divide the number of moles of each reactant by their corresponding coefficient in the equation
The reactant with the smaller molar ratio than the other reactants is the limiting reactant
Gases
At the same temperature and pressure, equal volumes of gases contain the same number of particles
1 mole of gas occupies 22.7 dm^3 at Standard Temperature and Pressure (STP) (273K & 100kPa)
V = n * 22.7 dm^3
Determining Process
Given a volume of a gas at STP, divide it by 22.7 dm^3 mol-1 to get the number of moles
2, Make use of the balanced equation to get the number of moles for the other gas
Multiply the number of moles of the other gas by multiplying it by 22.7 dm^3 mol-1 to get its volume
Ideal Gas Equation
PV = nRT
P = pressure
V = volume
n = number of moles
R= universal gas constant (8.31 J K-1 mol-1)
T = temperature in Kelvin
Definition
Purpose