Stoichiometry

Avogadro’s Law

the volume occupied by one mole of gas known as molar volume is the same for all gases when measured at the same temp and pressure contain equal number of particles

molar volume

he volume occupied by one mole of gas

STP definition

standard temperature and pressure

STP number

at STP one mole of gaseous atom has a volume of 22.7 dm3mol-1 the conditions at this number are 0 celsius, pressure of 100kPa

Vm

molar volume

pyramid for molar volume

V= n xVm

cm3 to dm 3

divide by 1000

dm3 to m3

divide by 1000

elementary entity

may be an atom, a molecule, an ion, an electron, any other particle or a specified group of particles

empirical formula

gives the simplest whole number ratio of atoms of each element present in that compound.

molecular formula

gives the actual number of atoms of each element present in a molecule, which may be the same as the empirical formula or a multiple of the empirical formula.

molar concentration

• The concentration of an aqueous solution can be expressed by the molar concentration, determined by the amount of solute and the volume of solution.

aqueous

substance is dissolved in water

complete combustion

Here the hydrocarbon will burn out completely with the oxygen and leave only two byproducts, water, and carbon dioxide

limiting reactant

The 

limiting reactant

 is the reactant which is always fully used up.

excess reactant

remains at the end of the reaction, is not all used up

theoretically yield

The 

theoretical yield

 that we calculate represents the amount that should be produced if a reaction is fully carried out under ideal conditions.

factors causing less product then expected

• Loss of product: some of the product may evaporate or simply be spilled. It may also be lost when isolating or purifying the product.

• Incomplete reaction: there may be impurities present or the reaction may not go to completion due to insufficient time.

• Alternative reactions: an unexpected side reaction may occur which results in a different product.

• One or more of the reactants is impure.

percentage yield

experimental yield/theoretical yield×100%

high vs low percentage yield

A high percentage yield (i.e. close to 100%) indicates that the reaction was very efficient at converting reactants into products while a low percentage yield suggests that some of the starting materials may have been wasted or converted into other unwanted byproducts via an alternative reaction.

atom economy

This is a measure of the reaction efficiency with respect to the total mass of reactant atoms which end up as desired products, represented as a percentage

percent atom economy

Molar mass of desired product/Molar mass of all reactants×100

relative molecular mass

 the average mass of a molecule; compared to 1/12 of (the mass of) one atom of ¹²C / compared to C – 12 taken as 12;

Or

average mass of a moleculemass of 1/12 of one atom of 12C

To calculate the mass percent

we divide the mass of the element in 1 mole of the compound by the compound's molar mass and multiply the result by 100.