molar volume of an ideal gas
22.7 dm3 mol–
what to do when a reaction involves aqueous solutions
this process is essentially the same, but now the moles will be converted using n = CV where C is the concentration and V is the volume of the aqueous solution
why are mole rations especially useful
they allow you to easily convert the mole values to a mass, volume or concentration of a particular chemical species, depending on whether it is a solid, liquid, gas or an aqueous solution.
the steps to summarise how to determine the mass, volume or concentration of an unknown reactant or product:
- Balance the equation. Identify the known reactant/product and unknown reactant/product.
- Convert the ‘known’ mass, concentration or volume given the question into moles.
- Use the mole ratio of a balanced chemical equation to determine the moles of the unknown value.
- Convert the moles value into the required quantity (mass, concentration or volume). Remember – if the question asks for ‘amount’ of something then it is acceptable to leave the answer in moles.
how is the quantity of aqueous solution measured
mass, not volume
limiting reactant
the reactant which is always fully used up
what determines the yield of the product formed
limiting reactant
steps to determine limiting reactant
- Calculate the number of moles of each reactant.
Divide the number of moles of each reactant by their coefficient in the reaction. Compare the two numbers – the smaller number is the limiting reactant.
Use the original moles of limiting reactant, and the mole ratio to calculate the yield of the product in focus.
excess reactant
the one which is remaining after the reaction has taken place
theoretical yield
the amount that should be produced if a reaction is fully carried out under ideal conditions
what always decides the theoretical yield
limiting reactant
what factors can cause the theoretical yield to be less
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.
when can the experimental yield be greater than the theoretical yield
can occur when there are impurities present in the product
also occur if the product undergoes subsequent reactions with its surroundings, such as oxidising or decomposing over time
convenient way to campare theoretical and experimental yield
percentage yield
percentage yield
experimental yield actually produced by the reaction compared to the theoretical yield, expressed as a percentage.
what does the percentage yield represent
the efficiency of the conversion of reactants into products
percentage yield equation
(experimental yield / theoretical yield) x 100
what does a high percentage yield indicate
the reaction was very efficient at converting reactants into products
what does a low percentage yield indicate
some of the starting materials may have been wasted or converted into other unwanted byproducts via an alternative reaction
what are some substances that do not naturally occur are produced by chemical reactions
medications, food additives or synthetic polymers
by-products
an additional product that is formed alongside the desired product during a chemical reaction
efficiency of the reaction can also be tracked by another metric other than percentage yield
atom economy
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
atom economy equation
% atom economy = (molar mass of desired product / molar mass of all reactants) x 100
