3.4 Reacting quantities

The ratio of moles of substances in a balanced equation

To find: The quantities of reactants required to prepare a required quantity of a product The quantities of products that should be formed from certain quantities of reactants

• Set up apparatus - Flask and a gas syringe • Weigh a sample of the metal and add it to the flask • Using a measuring cylinder, add 25.0cm^3 1.0mol dm^-3 HCl to the flask and quickly replace the bung • Measure the maximum volume of gas in the syringe

The maximum possible amount of product

The reaction may not have gone to completion Other reactions (side reactions) may have occurred alongside the main reaction Purification of the product may result in loss of some product

Usually lower than the theoretical yield The actual amount of product formed

Percentage yield = 100(actual yield/theoretical yield)

The reactant that is not in excess and will be completely used up first, stopping the readtion

Eg. 2H2+O2 If the same amount of both substances are allowed to react, hydrogen will be used up first and half of the oxygen will remain unreacted, therefore the limiting reagent is hydrogen. Then calculations must be based on hydrogen

A measure of how well atoms have been utilised

…produce a large proportion of desired products and few unwanted waste products, and are important for sustainability as they make best use of natural resources

Atom economy = 100(sum of molar masses of desired products/sum of molar masses of all products)

Look at atom economy Look at how readily available reactants are Look at efficiency and percentage yields