Stoichiometry

Review: What does a balanced equation indicate? 1. Quantitative information (how much) 2. Qualitative information (what) 2H2O2 2H2O + 1O2 2 molecules H2O2 2 molecules H2O + + 1 molecule O2 Also…

OR 2H2O2 2H2O + 1O2 68 g 36 g + 32 g 34 g 18 g + 16 g 17 g 9 g + 8 g It is the same as saying: 2 moles H2O2 2 moles H2O + 1 mole O2 OR 2 (2 + 32) 2 (2 + 16) 68 g 36 g + 32 g Reduce: Divide everything by 2. 34 g 18 g + 16 g Reduce: Divide everything by 2. 17 g 9 g + 8 g

Lizzy’s Delicious Salad 4 tomatoes + 7 chick peas + 20 lettuce pieces 1 delicious salad OR 4 doz. tomatoes + 7 doz. chick peas + 20 doz. lettuce pieces 1 dozen delicious salads * Same ratio, same salad composition

Problem: Lizzy needs to make her salad with 10 doz Problem: Lizzy needs to make her salad with 10 doz. chick peas for her dinner guests. How many doz. lettuce pieces will she need? 4 doz. tomatoes + 7 doz. chick peas + 20 doz. lettuce pieces 1 dozen delicious salads 20 doz. lettuce pieces 10 doz. chick peas x 29 = ______ doz. lettuce pieces 7 doz. chick peas

*Remember, Lizzy needs 29 doz. pieces of lettuce. Lizzy needs to make her salad with 10 doz. chick peas for her dinner guests. What weight of lettuce will she need? *Remember, Lizzy needs 29 doz. pieces of lettuce. Looking at her Delicious Salad Table as a resource, Lizzy’s notes: 1 doz chick pieces = 9 oz. 1 doz. lettuce pieces = 4 oz. 1 doz. tomatoes = 18 oz. 4 oz. 29 doz. Lettuce x pieces 116 = ______ oz. lettuce 1 doz. Lettuce pieces

Mole-Mole Ratios

MASS-MASS PROBLEMS How many grams of potassium chlorate must be decomposed to produce 288 grams of oxygen gas? 1. Write balanced equation. 2. Note what is being found. 3. Convert mass given into moles. 4. Use the mole ratio from the equation to find moles of what is being found. 5. Convert those moles into grams.

3 2 2 K+1 ClO3-1 O20 + K+1 Cl-1 O2 + KCl KClO3 How many grams of potassium chlorate must be decomposed to produce 288 grams of oxygen gas? 1. Write the balanced equation. K+1 ClO3-1 O20 + K+1 Cl-1 3 2 2 O2 + KCl KClO3

2 3 2 2. Note what is what is being found (X). X = g KClO3 O2 + KCl 3. Convert mass given into moles. 1 mole O2 9.00 288 g O2 (g) x = ______ moles O2 32.00 g O2 (g)

4. Use the mole ratio from the equation to find moles of what is being found. KClO3 KCl + O2 2 3 2 moles KClO3 9.00 moles O2 x 6.00 = ______ moles KClO3 3 moles O2

5. Convert those moles into grams. SHOW GUMMY BEAR VIDEO! 5. Convert those moles into grams. 122.55 g KClO3 6.00 moles KClO3 x 735 = ______ grams KClO3 1 mole KClO3 1 K + 1 Cl + 3 O 1 ( 39.10) + 1 (35.45) + 3 (16.00) = 122. 55 g

Practice mass-mass problems What mass of carbon dioxide is produced by the combustion of 342 grams of octane, C8H18? X = g 2 1 25 16 8 CO2 + H2O 18 9 C8H18 + O2 12.5 Multiply all coefficients by 2. 1 mole C8H18 342 g C8H18 x 2.993 = _______ moles C8H18 114.26 g C8H18 8 C + 18 H 8 ( 12.01) + 18 (1.01) = 114. 26 g

X = g 2 C8H18 + 25 O2 16 CO2 + 18 H2O 2.993 moles C8H18 x 23.92 16 moles CO2 2.993 moles C8H18 x 23.92 = _______ moles CO2 2 moles C8H18 44.01 g CO2 23.92 moles CO2 x 1050 = ______ grams CO2 1 mole CO2

2 2 3 (.90)(490) = 441 g KCl X = g KClO3 KCl + O2 441 grams KCl x How many grams of oxygen will form when 490. grams of potassium chloride, that is 90% pure, is produced by the decomposition of potassium chlorate? X = g 2 KClO3 2 KCl + O2 3 (.90)(490) = 441 g KCl 1 mole KCl 441 grams KCl x 5.915 = _______ moles KCl 74.55 g KCl

X = g 2 KClO3 2 KCl + 3 O2 5.915 moles KCl x 8.873 8.873 moles O2 x 32.00 g O2 8.873 moles O2 x 284 = _____ grams O2 1 mole O2

2 1 1 1 Mg0 + H2O Mg+2 OH-1 + H20 + H2 Mg + H2O Mg(OH)2 Magnesium reacts with steam to form magnesium hydroxide and hydrogen. How many moles of water are needed to form 95.7 g of magnesium hydroxide? Mg0 + H2O Mg+2 OH-1 + H20 2 1 1 1 + H2 Mg + H2O Mg(OH)2

1 2 1 1 X = moles Mg + H2O Mg(OH)2 + H2 1 Mg + 2 O + 2 H 1 mole Mg(OH)2 95.7 g Mg(OH)2 x 1.6406 = _______ moles Mg(OH)2 58.33 g Mg(OH)2 1 Mg + 2 O + 2 H 1 ( 24.31) + 2 (16.00) + 2 (1.01) = 58. 33 g

Mg + 2H2O Mg(OH)2 + H2 3.28 X = moles 2 moles H2O 1.6406 moles Mg(OH)2 x 3.28 = ______ moles H2O 1 moles Mg(OH)2

Mass-volume problems In a given equation, given a mass, find volume (or vice versa). *1 mole of any gas occupies ______ liters at STP. STP = standard temperature & pressure. 22.4 At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable Diatomic gas; with the molecular formula H2.

STP Standard temperature = 0° C or 273 K Standard pressure = 1 atmosphere (1 atm) or 760 mm Hg

Potassium chlorate decomposes to form 336 liters of oxygen Potassium chlorate decomposes to form 336 liters of oxygen. How many grams of potassium chloride are formed (at stp)? 1. Write balanced equation. 2. Note what is being found. 3. Convert liters into moles X = grams 2 KClO3 2 3 KCl + O2 1 mole O2 336 L O2 x 15.0 = ______ moles O2 22.4 L O2

2 3 KClO3 KCl + O2 1 K + 1 Cl 1 (39.10) + 1 (35.45) = 74.55 g KCl X = grams KClO3 KCl + O2 2 3 4. Use the mole ratio from the equation to find moles of what is being found. 5. Convert those moles into grams. 2 moles KCl 10.0 15.0 mol O2 x = ______ moles KCl 3 moles O2 74.55 g KCl 10.0 mol KCl x 746 = ______ grams KCl 1 mole KCl 1 K + 1 Cl 1 (39.10) + 1 (35.45) = 74.55 g KCl

Fe+3 O-2 + CO Fe0 + CO2 2 Fe + 3 O 2 (55.85) + 3 (16.00) = How many liters of carbon dioxide at stp can be produced by reacting 25.8 g of iron(iii) oxide as follows: Fe+3 O-2 + CO Fe0 + CO2 X = L 1 + CO 3 2 Fe + CO2 3 Fe2O3 1 mole Fe2O3 .1615 25.8 g Fe2O3 x = _______ moles Fe2O3 159.70 g Fe2O3 2 Fe + 3 O 2 (55.85) + 3 (16.00) = 159.70 g Fe2O3

X = L Fe2O3 + 3 CO 2 Fe + 3 CO2 .1615 mol Fe2O3 x .4845 3 moles CO2 .1615 mol Fe2O3 x .4845 = _______ moles CO2 1 mole Fe2O3 22.4 L CO2 .4845 mol CO2 x 10.9 = ______ L CO2 1 mole CO2

Volume-volume problems (assume stp) How many liters of nitrogen are needed to form 500. liters of ammonia in the Haber process? X = L 1 3 2 N2 + H2 NH3 1 moles NH3 500. L NH3 x 22.32 = ________ moles NH3 22.4 L NH3 Haber process is production of ammonium from N and H used in explosives. Haber was a German and this helped the Germans in WWI 1 mole N2 22.32 mol NH3 x 11.16 = ________ moles N2 2 moles NH3

1 3 2 N2 + H2 NH3 *Volumes of gases in a chemical reaction are X = L N2 1 + H2 3 2 NH3 22.4 L N2 250. 11.16 mol N2 x = _____ L N2 1 mole N2 *Volumes of gases in a chemical reaction are in the same ratio as their moles.

Avogadro’s hypothesis Equal volumes of gases at the same temperature and pressure contain the same number of molecules. 22.4 L O2 N2 At STP 1 mole 1 mole 6.02 x 1023 molecules 6.02 x 1023 molecules

What volume of oxygen is needed to completely burn 62 What volume of oxygen is needed to completely burn 62.0 liters of methane? X = L 1 CH4 + O2 2 1 CO2 + H2O 2 2 L O2 62.0 L CH4 x 124 = ______ L O2 1 L CH4 CAN ONLY DO RATIO WHEN L TO L OR MOL TO MOL; SO DO IN 3 STEPS IF CAN’T REMEMBER WHEN ABLE TO DO RATIO! CAN ONLY USE MOL RATIO WHEN IT IS LITERS TO LITERS!

Passing an electric discharge through oxygen gas produced ozone (O3) Passing an electric discharge through oxygen gas produced ozone (O3). How many liters of ozone are formed from 5.33 moles of oxygen? X = L O2 O3 3 2 2 moles O3 5.33 moles O2 x = ______ mole O3 3.553 3 moles O2 3.553 moles O3 x 22.4 L O3 = ______ L O3 79.6 1 mole O3

Nitrogen gas combines with oxygen gas in an automobile engine to form nitrogen (iii) oxide gas: 2 N2 + 3O2 2N2O3. How many moles of nitrogen combines with 8.75 moles of oxygen 2 moles N2 8.75 moles O2 x = ______ moles N2 5.83 3 moles O2 CAN ONLY DO RATIO WHEN L TO L OR MOL TO MOL; SO DO IN 3 STEPS IF CAN’T REMEMBER WHEN ABLE TO DO RATIO!

X = L Given: N2 + 3 H2 2 NH3 What volume of ammonia (NH3) is produced from 3.75 moles of hydrogen (at stp)? 2 moles NH3 3.75 moles H2 x = ______ moles NH3 2.5 3 moles H2 22.4 L NH3 2.5 moles NH3 x = ______ L NH3 56.0 1 mole NH3

1 mole = G.F.M 1 mole = 22.4 L mole ratio g L g L What you want What you want to get rid of Note: *To cross out unwanted units, the units must be on opposite sides of the *The unit you are solving for must be the last unit on top that is NOT crossed out.

Multiply by mole ration (from equation) Given mass, find mass Given volume GRAMS given LITERS given Convert to moles 1 mole GFM of given x Convert to moles 1 mole 22.4 L x If given, moles start here MOLES given MOLES given Multiply by mole ration (from equation) If want liters (volume): MOLES of substance desired If want moles, stop here convert VOLUME of substance desired x 22.4 to liters 1 mole Convert to grams GFM desired substance 1 mole x GRAMS of substance desired

What mass of sodium chloride can be produced by the reaction of 0 What mass of sodium chloride can be produced by the reaction of 0.5 liter of chlorine with sodium at stp? 2 1 2 Na + Cl2 NaCl 1 mole Cl2 0.5 L Cl2 x .02 = ______ moles Cl2 22.4 L Cl2 2 moles NaCl .04 .02 mol Cl2 x = ______ moles NaCl 1 mole Cl2

What mass of sodium chloride can be produced by the reaction of 0 What mass of sodium chloride can be produced by the reaction of 0.5 liter of chlorine with sodium at stp? 58.44 g NaCl .04 mol NaCl x 2.6 = ______ grams NaCl 1 mole NaCl

Another Mole Map g MOLE # particles (atoms & molecule) liters