Unit 6 - Stoichiometry & Chemical Formulas - Regents Flashcards
What are the three types of Chemical Formulas?
- Empirical Formula
- Molecular Formula
- Structural Formula
Definition of Empirical Formula (3)
Definition & Useful
- Simplest Ratio of Atoms
- All Ionic Compounds Formulas are Empirical
- Covalent Formula can be Empirical too
Why are all ionic compound formulas empirical?
They do not form a discrete molecule, but rather a crystal lattice, so there’s no point in have unsimplified ratios
Definition of Structural Formula (2)
Definition & Useful
- Provides info on HOW elements are bonded
- Only useful for covalent compounds
Definition of Molecular Formula (3)
- Actual number of atoms per element
- May be multiple of the empirical formula
- May be the same as the empirical formula
Definition of Molecular Weight/Formula Mass
Sum of masses of atoms in the molecule
What is “u” short for?
Atomic Mass Units
How do you find the molecular formula when given percent compositions? (5)
- Find Empirical Formula
- Find Molecular Weight of E. Form.
- Molecular Weight/Given Molar Mass
- Round Quotient (nearest ones place)
- Multiply all subscripts by quotient
How do you determine the Empirical Formula when given percent compositions? (5)
- Change all % to grams (Ex: 22.1% to 22.1 g)
- Identify atomic mass of elements in PT (Ex: Al - 27)
- Divide grams by the molar mass (Ex: 22.1/27 = 0.82)
- Divide the quotients of each element by the smallest quotient (Ex: 3.3/0.82 & 0.82/0.82)
- A Ratio is Formed (if a decimal, take smallest multiple) (Ex: 1:1.5 = 2:3)
Ex:
Element - Percent to Gram - Molar Mass - Quotient - Ratio
Al - 22.1 - 27 - 0.82 - 1
P - 25.4 - 31 - 0.82 - 1
O - 52.5 - 16 - 3.3 - 4
AlPO4
What are the four types of Chemical Reactions?
- Synthesis
- Decomposition
- Single Replacement
- Double Replacement
Definition of Synthesis Rxn
Elements/Compounds Combine for a more Complex Compound
Ex: A + X = AX
Definition of Decomposition Rxn
Complex Compounds Breaks Down to Simpler Compounds
Ex: AX = A + X
Definition of Single Replacement Rxn
An element replaces another element in a compound
Ex: A + XY = X + AY
Definition of Double Replacement Rxn
One of the elements in each of the compounds are interchangeable
Ex: AB + XY = AY + XB
What are the 4 Cardinal Rules when Balancing Equations?
- Count each type of atom on both sides of the equation
- If a polyatomic ion remains intact on both sides, leave it alone
- NEVER CHANGE THE SUBSCRIPTS
- Automatically Convert H2O as HOH
What is the difference between the moleular weight, formula mass, molar mass and gram formula mass?
Molecular Weight - Covalently Bonded Molecules
Formula Mass - Ionic Compounds
Molar Mass - Mass of one mole (g/mol)
Gram Formula Mass - Same as Molar Mass, but specific to ionic compounds
ALL HAS THE SAME VALUE
Molecular Weight of H20 - 18 g
Formula Mass of H20 - 18 g
Molar Mass of H20 - 18 g/mol
Gram Formula Mass of H20 - 18 g/mol
Definition of Mole (3)
- A way to count a large quantity of very small particles
- 1 mole = 6.022 × 10²³ (Avogadro’s number)
- A “dozen” counts 12 items, a “mole” counts 6.022 × 10²³ particles
How do you write the Molar Mass?
Formula Mass & add units g/mol
What do coefficients in a balanced equation actually indicate?
Mole - Mole Ratios between Reactants & Products
Ex: 2H₂ + O₂ – 2H₂O
- 2 moles of H reacts with 1 mole of O to produce 2 moles of water
- For every mole of O, 2 moles of water is created
- 5 moles of O will react with 10 moles of H to produce 10 moles of water
Definition of Percent Composition
Expresses relative amount of each element in a compound (%)
% Comp. = (MassofElementinCompound/TotalMassofCompound) x 100
