1. Stoichiometric Relationships
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What is a mole?
A unit that measures the amount of substance.
How many elementary entities are in one mole?
6.02 x 10^23
What is an elementary entity?
Any particle. Eg: an atom, molecule or ion.
N= ?
n x NA
What is the molar mass?
The mass of one mole of an element/ compound.
n= ?
m/ M
N/ NA = ?
m/ M
Define ‘molecular formula’.
The actual number of atoms in a compound.
Define ‘empirical formula’.
The simplest whole number ratio of atoms in a compound.
What are the units for molar mass?
gmol-1
How do you find the limiting reactant?
Divide the given moles by the stochiometric coefficient.
Define ‘theoretical yield’.
The mass of product formed if reactants react completely, according to molar ratios.
Define ‘actual yield’.
The mass of product obtained in a reaction.
Define ‘percentage yield.’
A measure of the reaction efficiency.
What is the formula for percentage yield?
(Actual yield/ theoretical yield) x100
Give 5 reasons why a reaction may not be 100% efficient.
• Transfer losses (left in glassware) • Side reactions. • Reaction reaches equilibrium. • Reactants may be impure. • Reaction is slow.
Define ‘atom economy’.
A measure of efficiency that assesses how many reactant atoms are transformed to the desired products.
What is the formula for atom economy?
Atom economy= (Mr of desired product/ sum of Mr of all products) x100
Give 2 ways that atom economy can be improved.
• Undesired products can be recycled within a chemical plant. • Undesired products can be bought by another company for another process.
For gases, moles= ?
volume / molar volume
State Avogadro’s Law.
The volume of gas is directionally proportional to the number of moles.
At stp, how much volume does one mole of gas occupy?
22.7 dm-3
What are the values of standard temperature and pressure?
273K and 100KPa
What is a homogeneous reaction?
A reaction where all of the species are in the same phase.