Unit 4: Stoichiometry Stoichiometry

Chemical Equations and the Mole Remember: a chemical equation is like a recipe – it tells you the ingredients (reactants) you need to make certain products chemical equations tell you the relative quantities of reactants and products in a reaction

Chemical Equations and the Mole How many moles do you have of each of the following? Frame (F): Seat (S): Wheel (W): Handlebar (H): Pedal (P): Tricycle (FSW3HP2): 1 mole 3 moles 2 moles

Chemical Equations and the Mole Example: If you had 4 moles of S and an excess of all the other reactants, how many tricycles (FSW3HP2) could you make? We can apply the tricycle example to chemical reactions.

Stoichiometry Stoichiometry: Using a known amount of one substance to predict how much of a reactant will be used or how much of a product will be produced. You can use stoichiometry to answer questions like: Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen. N2 + H2 → NH3

Stoichiometry – The Box Method Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen. N2 + 3H2 → 2NH3 Step 1: Balance the equation.

Stoichiometry – The Box Method Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen. N2 + 3H2 → 2NH3 grams 5.40 g * molar mass 28.02 g/mol 17.034 g/mol moles Step 2: Construct the box and fill in known information (starting amount and molar masses).

Stoichiometry – The Box Method Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen. N2 + 3H2 → 2NH3 grams 5.40 g *6.54 g molar mass 28.02 g/mol 17.034 g/mol moles 0.192 mol 0.384 mol MORE x 2/1 Step 3: Calculate missing information until you determine what the problem is asking you to find.

Stoichiometry – The Box Method Calculate the number of grams of NH3 produced by the reaction of 5.40 g of nitrogen with an excess of hydrogen. N2 + 3H2 → 2NH3 grams 5.40 g *6.54 g molar mass 28.02 g/mol 17.034 g/mol moles 0.192 mol 0.384 mol MORE x 2/1 Step 3: Calculate missing information until you determine what the problem is asking you to find.

Stoichiometry – Practice! How many grams of water would be produced from 60 grams of H2 and an excess of O2? __H2 + __O2 → __H2O

Stoichiometry You can use stoichiometry to answer questions like: Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen. N2 + H2 →NH3 Steps: Balance the equation. Convert mass to moles. 3. Convert moles of ‘known’ to moles of ‘unknown’ using the mole ratios (coefficients) from the balanced equation. 4. Convert moles of ‘unknown’ to mass ‘unknown’.

Stoichiometry – Step 1 N2 + H2 →NH3 Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen. N2 + H2 →NH3 Step 1: Balance the equation.

Stoichiometry – Step 2 N2 + H2 →NH3 Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen. N2 + H2 →NH3 Step 2: Convert mass to moles.

Stoichiometry – Step 3 N2 + H2 → NH3 Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen. N2 + H2 → NH3 Step 3: Convert moles of ‘known’ to moles of ‘unknown’ using the mole ratios (coefficients) from the balanced equation.

Stoichiometry – Step 4 N2 + H2 →NH3 Calculate the number of grams of NH3 produced by the reaction of 5.40 g of hydrogen with an excess of nitrogen. N2 + H2 →NH3 Step 4: Convert moles of ‘unknown’ to mass ‘unknown’.