C3

• what is the formula for percentage mass of an element in a compound?

  atomic mass x number of atoms of that element / relative formula mass of compound x 100
• avagadro's constant = 6.02 x 10^23
• one mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass
• number of moles = mass in grams of an element or compound / relative atomic mass
• if mass seems to change during a reaction there's usually a gas involved
• if mass increases in a reaction it's probably because one of the reactants in a gas that's found in the air and all products are solids, liquids or aqueous
• if the mass decreases in a reaction it's probably because one of the products is a gas and all the reactants are solids, liquids or aqueous
• you can work out the balanced symbol equation of the reaction if you know the mass of the reactants and products
• to work out balance equations using reacting masses, divide the mass of each substance by its relative formula mass to find number of moles, divide number of moles of each substance by smallest number of moles in reactions, if any numbers aren't whole multiply them all by the same number so they all become whole and use these numbers in front of each chemical formula in a balanced equation
• reactions stop when one reactant is used up
• the reactant that's used up in a reaction is the limiting reactant
• one mole of any gas occupies 24dm^3 at room temperature
• volume of gas = mass of gas / relative formula mass of gas
• concentration in mol/dm^3 = number of moles of solute / volume of solvent
• concentration in g/dm^3 = mass of solute / volume of solvent
• number of moles = concentration x volume
• atom economy = relative formula mass of desired product / relative formula mass of all reactants x 100
• higher the atom economy the greener the product is