1. Stoichiometric Relationships Flashcards
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.
What is a heterogeneous reaction?
A reaction where the species are in different phases.
Density= ?
Mass/ volume
State the 5 assumptions of an ideal gas.
- Gas molecules are in a constant, random motion.
- Molecular collisions are perfectly elastic.
- The volume occupied by gas molecules is negligible.
- There are no intermolecular forces.
- Kinetic energy is directionally proportional to temperature in Kelvin.
At which temperatures do real gases act least like ideal gases?
At low temperatures, kinetic energy falls. Upon collision, attractive forces form and collisions are not elastic.
At which pressures do real gases act least like ideal gases?
At high pressures, there are more molecules in the space so the volume of particles becomes more significant.
In which conditions does a gas behave like an ideal gas?
High temperatures and low pressures.
(P1V1) / T1= ?
(P2V2) / T2
PV= ?
nRT
What is the formula for percentage uncertainty?
(Total uncertainty/ measured uncertainty) x100
What are the units for Avogadro’s constant?
mol-1
concentration= ?
moles x volume
How many dm3 is 1cm3
0.001
What is the formula for ppm?
Ppm= (mass/ total mass of solution) x 1,000,000
C1V1= ?
C2V2
