Stoichiometry

Definitions Stoichiometry - deals with mole, mass and volume relationships in chemical reactions Limiting reactant - controls the amount of product formed There is no more at the end of the reaction

What are we going to do? From the balanced equation, we can predict the amount of product if given the amount of reactant From the balanced equation, we can predict the amount of reactant needed if given the desired amount of product

What do we need to know? Mole Ratio – will help convert moles of one compound in a balanced chemical equation into moles of another compound. Example: Reaction between magnesium and oxygen to form magnesium oxide. ( fireworks) 2 Mg + O2  2 MgO Mole Ratios: 2 mole : 1 mole : 2 mole

Why is this important? Stoichiometry is used in chemical engineering in order to understand/predict chemical reactions. Production of items include: soap, tires, fertilizer, gasoline, deodorant, and chocolate bars Real-life applications in chemical engineering as well as research Therefore, stoichiometry is one of the most important and fundamental topics in chemistry.

Mole to Mole Stoichiometry

Mole – Mole Stoichiometry… Write the balanced equation Determine which is the starting chemical (A) and which is chemical we want to end up with (B) Use coefficients of balanced equation to convert moles of chemical A to moles of chemical B Mole ratio!

Some Practice **Remember, UNITS FIRST** How many moles of water can be obtained from the reaction of 4 moles of O2? 2 H2 + 1 O2 → 2 H2O 4 mol O2 1 x 2 mol H2O 1 mol O2 = 8 mol H2O Mole Ratio

Practice… In order to produce 15 moles of water, how many moles of oxygen must be reacted? 2 H2 + 1 O2 → 2 H2O

Homework – Worksheet #1 Chemical Reactions – add to HW before you leave! __ Fe + __ O2  __ Fe2O3 __ N2 + __ H2  __ NH3 __ H2 + __ O2  __ H2O (and 5) __ Mg + __ HCl  __ H2 + __ MgCl2 (and 7) __ H2SO4 + __ NaOH  __ H2O + __ Na2SO4

Gram <-> Mole Stoichiometry Allows you to calculate the mass of product produced or the mass of reactant needed.

How do we do this? Write the balanced equation Steps : Determine which is the starting chemical (A) and which is chemical we want to end up with (B) Steps : Convert gA to molA Use GFW Convert molA to molB Use stoichiometry rules Convert molB to gB

Visualizing it a different way Moles of “A” Mole Ratio Moles of “B” GFW GFW Grams of “A” Grams of “B”

Mass-Mass Calculations *Remember, UNITS FIRST!!* How many grams of SnF2 can be produced from the reaction of 30.00 g of HF with Sn? Sn + 2 HF → SnF2 + H2 30.00 g HF 1 1 mole HF 20.01 g HF x 1 molSnF2 2 mol HF x 156.71 g SnF2 1 mol SnF2 x GFW HF Mole Ratio Answer = 117.5 g SnF2 GFWSnF2

Let’s do some practice… The combustion of a sample of butane, C4H10 (lighter fluid), produced 2.46 grams of water. 2 C4H10 + 13 O2 -------> 8 CO2 + 10 H2O How many grams of butane were used?

Some more practice… Iodine chloride, ICl, can be made by the following reaction between iodine, I2, potassium iodate, KIO3, and hydrochloric acid. 2 I2   +   KIO3  +  6 HCl  ->   5 ICl  +  KCl  +  3 H2O Calculate how many grams of iodine are needed to prepare 10.3 grams of ICl by this reaction.

Stoichiometry with grams, moles and liters…

How do we do this? Putting all the steps together…. Write the balanced equation Determine which is the starting chemical (A) and which is chemical we want to end up with (B) Steps : Convert LA/gA (whichever is given) to molA Use GFW if given grams Convert molA to molB Use stoichiometry rules Convert molB to gB/LB Use GFW if asking for grams

Looking at it another way Moles of “A” Mole Ratio Moles of “B” GFW or Liter Conv. GFW or Liter Conv Liters or Grams of “A” Liters or Grams of “B”

Practice Problem Nickel metal reacts with silver nitrate solution according to the following balanced equation.              Ni + 2 AgNO3 ----------->  2 Ag + Ni(NO3)2 If 21.4 L of silver nitrate solution reacts with an excess of nickel metal, calculate the mass of silver produced.