Reaction Stoichiometry When an equation is balanced it tells us the number of moles that are required for the reaction to proceed. We can also use the information to determine the amount of product produced. 2AgNO3(aq) + CuCl2(aq) → 2AgCl(s) + Cu(NO3)2(aq) This tells us that for every 2 moles of silver nitrate that reacts we get 1 mole of copper nitrate produced. However in most cases we don’t go from moles to moles. We need to go from mass to mass

Mg + H2SO4 → MgSO4 + H2 What mass of hydrogen gas would be evolved if 6.075g of magnesium reacted completely with dilute sulfuric acid? Step 1: Balance the equation balanced Step 2: Convert the mass of reactants into moles 1 mole Mg= 24g 6.075g = x moles X= 6.075/ 24 = 0.25 moles

Step 3: Use your mole ratio’s to determine number of moles of product 1 mole Mg: 1 mole H2 0.25 moles Mg: 0.25 moles Mg Step 4: Convey number of moles into mass 1 mole H2: 2g 0.25 moles = 2 x 0.25 = 0.5g

Hydrazine, N2H4, is a rocket fuel which reacts with oxygen producing gaseous products of nitrogen and water under very high pressures. If 6.4x104kg of hydrazine is burned completely, what mass of water vapor will be produced? Step 1: Step 2: Step 3: Step 4

Molarity The relationship between the number of moles and concentration of a solution is given by the triangle Number of moles n Concentration, mol/l c v Volume, l

If 117g of sodium chloride is dissolved in 250cm3 of water If 117g of sodium chloride is dissolved in 250cm3 of water. Calculate the concentration of the solution. Step 1: Determine the formula using the cross- over method Na Cl NaCl 1 1 1 1 Step 2: Calculate the number of mole of the substance 1 mole NaCl = 58.5g 117g = 117/ 58.5 moles = 2 moles

Step 3: convert volume into litres ml/ cm3  l = divide 1000 250/ 1000 = 0.25l Step 4: Use the triangle to solve the problem c = n/v = 2/ 0.25 = 8mol/l