Stoichiometry

Inquiry Activity Using 20 white balls (H), make 10 diatomic molecules. Make diatomic molecules using the yellow balls as well. Without looking, have someone choose 10 molecules at random. Out of the chosen molecules, pair up the reactants using the following chemical equation: Y2 + 3W2  2YW3 Pair up reactants until you run out of one of the reactants. This is your limiting reagent. Repeat the activity and see if you get the same results

Review – Balance these equations N2 + H2  NH3 H2S + O2  SO2 + H2O H2 + I2  HI

Stoichiometry Study of the amount of substances consumed or produced in a chemical reaction – Requires Balanced Equations! Reactants  Products

Reactants and Products Reactants and Products SOMETIMES the same Stoichiometry Reactants and Products ALWAYS the same Reactants and Products SOMETIMES the same Number of Atoms Mass Number of molecules Moles Volume N2 + 3H2  2NH3 Atoms 2 N 6 H = 2 N + 6 H Mass 28g + 6g = 34g Number of molecules 1 molecule 3 molecules 2 molecules Moles 1mole 3 moles 2moles Volume 22.4L 64.2L 44.8L

What is conserved in each reaction. Atoms. Mass. Number of Molecules What is conserved in each reaction? Atoms? Mass? Number of Molecules? Moles? H2 + O2  H2O H2 + I2  2HI C2H2 + O2  CO2 + H2O

Calculations Mole ratio: Conversion factor using the coefficients of balanced chemical equations Used to convert between moles of reactant and moles of product N2 + 3H2  2NH3 1 mol 3 mol 2mol So….. 1 mol N2 2 mol NH3 3mol H2 3 mol H2 1 mol N2 2 mol NH3

How many moles of ammonia (NH3) are produced when 0 How many moles of ammonia (NH3) are produced when 0.6mol nitrogen (N2) reacts with hydrogen (H2)? Write the chemical reaction: What conversion do you use to get from N2 to NH3? Solve

Al + O2  Al2O3 How many moles of aluminum are needed to form 3.7mol of aluminum oxide? How many moles of oxygen are required to react completely with 14.8mol Al? How many moles of Al2O3 are formed when 0.78 mol O2 reacts with aluminum?

Mole – Mass Calculations Calculate the number of grams of NH3 produced by the reaction of 5.40g hydrogen with an excess of nitrogen. What is the chemical reaction? Conversion gram hydrogen  mol hydrogen  mol NH3  gram NH3

CaC2 + H2O  C2H2 + Ca(OH)2 How many grams of acetylene gas (C2H2) are produced by adding water to 5.00g CaC2? How many moles of CaC2 are needed to react completely with 49.0g H2O?

ALYWAYS CONVERT THROUGH USING MOLES!!! Other conversions… Number of particles - 1 mol 6.02x1023 particles Volume of gas at STP - 1 mol 22.4L So you should be able to convert: mass-mass mol-mol mass-mol mol-number of particles mol-volume of gas at STP ALYWAYS CONVERT THROUGH USING MOLES!!!

How many molecules of oxygen are produced when 29 How many molecules of oxygen are produced when 29.2g of water is decomposed? H2O  H2 + O2 How many grams of nitrogen dioxide must react with water to produce 5.0x1022 molecules of nitrogen monoxide? NO2 + H2O  HNO3 + NO

How many liters of nitrogen dioxide are produced when 34L of oxygen reacts with excess nitrogen monoxide? NO + O2  NO2

How much do you actually get? In any reaction, the amount of product formed is limited by the amount of reagents…. Limiting Reagent: -determines the amount of product that can be formed -is completely used up in the reaction Excess Reagent: - reactant is not completely used up

What is the limiting reagent when 80g of Cu reacts with 25g of S in the following reaction? Cu + S  Cu2S Balance the equation Convert grams to moles What is the mole ratio between Cu and S? Take the given mole quantity for one reagent (#2), multiply it by the mole ratio (#3) to find how many moles of the other reagent are needed Compare moles needed to moles you have to find which one is limiting

What is the limiting reagent if 6.0g HCl reacts with 5.0g Mg? If 2.70mol of C2H4 is reacted with 6.30mol O2, what is the limiting reagent? C2H4 + O2  CO2 + H2O What is the limiting reagent if 6.0g HCl reacts with 5.0g Mg? Mg + HCl  MgCl2 + H2

Limiting reagents can be used to find out how much product is actually made. What is the maximum number of grams of Cu2S that can be formed when 80.0 g Cu reacts with 25.0g S? Cu + S  Cu2S What is the limiting reagent? Use the limiting reagent to calculate the amount of product

How many grams of water can be produced by the reaction of 2 How many grams of water can be produced by the reaction of 2.40mol C2H2 with 7.4mol O2? C2H2 + O2  CO2 + H2O If 2.7mol C2H4 is reacted with 6.3mol O2, how many moles of water are produced? C2H4 + O2  CO + H2O

Things happen in lab… Theoretical yield: the maximum amount of product that could be formed Actual yield: the amount of product that is actually formed in lab Percent Yield = Actual yield x 100% Theoretical yield

What is the percent yield if 13. 1g CaO is actually produced when 24 What is the percent yield if 13.1g CaO is actually produced when 24.8g CaCO3 is heated? CaCO3  CaO + CO2