Amount of substance-physical chemistry Flashcards
What is relative atomic mass (Aᵣ)?
The average mass of an atom relative to 1/12 the mass of an atom of 12C
What is relative molecular mass (Mᵣ)?
The average mass of a molecule relative to 1/12 the mass of an atom of 12C
What is relative formula mass?
The average mass of a molecule relative to 1/12 the mass of an atom of 12C
What is the Avogadro constant?
The number of particles (atoms, molecules, or ions) in one mole of a substance.
Approximately 6.022 × 10²³ particles per mole.
What is a mole?
A mole is the amount of a substance that contains the same number of particles as there are atoms in 12g of carbon-12.
Can apply to atoms, molecules, ions, or electrons.
How do you calculate the number of particles in a given amount of substance?
Numberofparticles=
Moles×Avogadro’sconstant
How do you calculate moles from mass?
Moles = mass/mr
What is concentration and how is it calculated?
Concentration is the amount of solute (moles) per dm³ of solution:
Concentration = Moles/volume
What is the ideal gas equation? Give units
pV=nRT
p = pressure (Pa)
v = volume (m3)
n = number of moles
R = gas constant (Jmol-1K-1)
T = temperature (K)
What is the empirical formula?
The simplest whole-number ratio of atoms in a compound.
Example: Glucose (C₆H₁₂O₆) → Empirical formula = CH₂O.
What is the molecular formula?
The actual number of atoms of each element in a molecule.
Example: Benzene
Empirical formula = CH
Molecular formula = C₆H₆
How are empirical and molecular formulas related?
The molecular formula is a whole-number multiple of the empirical formula.
MolecularFormula=(EmpiricalFormula)×n
Where n is found using:
n = Mr/Empirical formula mass
How do you determine the empirical formula from mass or percentage?
Convert mass/percentage to moles using:
Mass or percentage/ Relative atomic mass
Divide by the smallest number of moles.
If needed, multiply to get whole numbers.
How do you determine the molecular formula?
Find the empirical formula mass (EFM).
n = Mr/Empirical Formula Mass
What are the key rules for writing and balancing equations?
Write correct formulas for all reactants and products.
Balance atoms by adjusting coefficients (not subscripts).
Check charges for ionic equations.
Include state symbols
What is the difference between a full equation and an ionic equation?
Full equation: Shows all reactants and products.
Ionic equation: Only shows the ions involved in the reaction, omitting spectator ions.
What is percentage atom economy, and how is it calculated?
Definition: Atom economy measures the efficiency of a reaction in converting reactants into useful products.
AtomEconomy=(TotalMassofReactant)/
(MassofDesiredProduct) x 100
What are the economic, ethical, and environmental benefits of high atom economy?
Economic: Less waste means lower costs and higher efficiency.
Environmental: Fewer waste products reduce pollution.
Ethical: Sustainable use of raw materials conserves resources.
How do you calculate percentage yield?
PercentageYield:
TheoreticalYield/ActualYield x 100
How do you calculate the volume of a gas at RTP?
At Room Temperature and Pressure (RTP): 1 mole of gas = 24 dm³
Formula:
Volume(dm³) = Moles × 24
