Reacting Quantities

Stoichiometry: The ratio of moles of each substance in a chemical reaction.
• Balanced Equation: The balancing numbers gives molar ratio.
• Find Moles- Various States: Can have solid go to gas or liquid. If asks to calculate volume of gas,
remember there might be more than one gas.
– Work out moles of mass using Mr Moles.
– Molar ratio to find unknown moles.
– Concentration Volume for liquid or Volume/ 24 for gas.
• Identifying Unknown Metal: Attach gas syringe to conical flask. Add metal. Add HCl to flask and
quickly replace bung. Measure maximum volume of gas in the syringe. Use equations and molar
ratio to find unknown metal.

Theoretical Yield: It is the yield resulting from complete conversion of reactants into products.
Impossible as…
– Reaction may not have gone to completion.
– Other reactions may have taken place alongside main reaction.
– Purification of product may result in loss of some product.
• Percentage Yield:
– Find theoretical yield of product using values of reactant given and molar ratio.
– Find actual yield from values of product that are actually produced in question. Must use
appropriate mole formula to work these values out.
– (Actual y/ Theoretical y) x 100.
• Limiting Reagent: The reactant that is not in excess so will be used first and stop reaction. If don’t
know limiting reagent, need to find out by working out moles of each reactant and comparing with
equation. Calculations based on limiting reagent.
• Atom Economy: (Sum of molecular masses of desired products)/ (Sum of molecular masses of all
products) x100. Only worked out from balanced equation. Remember to include balancing
numbers when calculating molar masses.
• Only one product formed so 100% atom economy.
• Named waste product produced as well so atom economy less than 100%.
• Advantages- more readily available starting materials. No toxic products. High atom economy,
100% (no waste products). Compound is regenerated- used again.
• Sustainability: Sustainability depends on both atom economy and % yields.
• Low atom economy means poor sustainability so need to develop use for waste products to
increase atom economy. Therefore stop greenhouse gas emission as waste product.
• High % yield sustainable as efficient conversion from reactant to product. High atom economy
reduces amount of waste products, so increases sustainability.