Stoichiometry

how many particles are in one mole

how many particles are in one mole

6.02 × 10²³

how do you find the number of moles (n) based on number of particles (N) and Avogadro’s constant (Na)

n = N / Na

how do you find the number of moles (n) based on mass (m) and molar mass (M)

n = m / M

how do you find the number of moles (n) based on volume (V) and molar volume (Mv)

n = V / Mv

how do find the number of moles (n) based on percentage mass (%m) and molar mass (M)

n = %m / M

how do you find the number of moles (n) based on volume (V) and concentration (c)

n = c x V

how do you convert cm³ to dm³

dm³ = cm³ / 1000

how do you find the number of atoms in 1 mole of NaCl

atoms = (6.02 × 10²³) x 2

define molecular formula

a sequence showing all elements in a particle, with the number of that element as the subscript (eg. NaCOOH)

define empirical formula

a sequence elements in a particle in the simplest ratio

How do you find the empirical formula?

you can always find the empirical formula by:

• finding the moles of each element (n)

• Dividing each n by the smallest n

• approximate to the nearest whole number

how do you find the molecular formula from the empirical formula?

• Find the empirical mass (the molar mass of the empirical formula)

• Divide the molecular mass by the empirical mass

• multiply all subscripts by this value

Define percentage composition by mass

the percentage of 1 element’s mass of the total mass

how do you find the percentage by mass from the empirical formula?

%m = (subscript x M of the element) / total molar mass

what does combustion mean

substance reacts with oxygen to form CO2 and H2O

A 1.00g sample of a compound containing carbon, hydrogen and oxygen undergoes complete combustion

What is Avogadro’s law?

equal volumes of gases, when measured at the same temperature and pressure, contain an equal number of particles

what is the molar volume?

the volume occupied by 1 mole of gas

at standard temperature (0C) and pressure (100kpa) this is 22.7 dm³/mol

How do you balance equations?

give each particle a coefficient such that the elements in the reactants are equal to the elements in the products

what is decomposition

when a substance breaks apart

Eg. CO → C + O

what is the limiting reactant

the reactant where (moles x ratio) is lowest

what is the unused reactant called in an equation

excess

how can you determine the limiting reactant

A = coefficient 1 / coefficient 2

B = n1 / n2

If A > B then 1 is the limiting reactant

If B > A then 2 is the limiting reactant

What is the percentage yield

this is a measure of the efficiency of a chemical reaction by comparing the experimental and theoretical yield

percentage yield calculation

percentage yield = [(experimental yield) / (theoretical yield)] x 100

experimental yield and theoretical yield in moles

what can cause imperfect percentage yields

loss, impurities, wastage or incomplete reactions

What is atom economy

the proportion of reactants that ends up in the desired product (tells you how efficient/sustainable a reaction is)

atom economy calculation

atom economy (%) = [(M of desired product) / (M of all reactants)] x 100

how do you find the percentage by mass from the masses?

%m = [(mass of element) / (mass of total substance)] x 100

define relative molecular mass

the mass of 1 molecule compared to 1/12 of a carbon-12 atom