Stoichiometry

What is STOICHIOMETRY?!@!? Stoichiometry refers to the calculations of chemical quantities from balanced chemical equations. Allows us to relate masses of reactants and products

Interpreting Chemical Equations Write the synthesis reaction of nitrogen reacting with hydrogen forming nitrogen trihydride. ……..and balance! ___ N2 (g) + ___ H2 (g)  ___ NH3 (g) coefficient – also represents ONE mole of N2 Mole ratios – the ratio of moles of one substance to moles of another substance in a balanced chemical equation 1 3 2

Interpreting Chemical Equations ___ N2 (g) + ___ H2 (g)  ___ NH3 (g) Mole ratios come from the coefficients of a balanced equation. This is also known as the mole conversion factor. Example Mole Ratios: 1 mol N2 3 mol H2 2 mol NH3 3 mol H2 3 mol H2 1 mol N2 1 mol N2 2 mol NH3 1 3 2

Mole-Mole Conversion Problems 1 N2 (g) + 3 H2 (g) 2 NH3 (g) How many moles of ammonia (NH3) can be made from 7 moles of nitrogen reacting with an excess of hydrogen?

Mole-Mole Conversion Problems 1 N2 (g) + 3 H2 (g) 2 NH3 (g) How many moles of ammonia (NH3) can be made from 7 moles of nitrogen reacting with an excess of hydrogen? 7 mol of N2 2 mol of NH3 14 mol of NH3 1 mol of N2 MOLE RATIO

Practice Problems How many moles of hydrogen (H2) are required to completely react with 8 moles of nitrogen to produce ammonia (NH3)? How many moles of nitrogen (N2) are needed to completely react with 6 moles of hydrogen to produce ammonia (NH3)?

Interpreting Chemical Equations ___ N2 (g) + ___ H2 (g)  ___ NH3 (g) How many grams of ammonia (NH3) can be made from reacting 39.0 grams of nitrogen reacting with an excess of hydrogen? 1 3 2

Mass-Mass Conversion Problems 1 N2 (g) + 3 H2 (g) 2 NH3 (g) How many grams of ammonia (NH3) can be made from reacting 39.0 grams of nitrogen reacting with an excess of hydrogen? 39 g of N2 1 mol of N2 2 mol of NH3 17 g of NH3 28 g of N2 1 mol of N2 1 mol of NH3 MOLE RATIO 47.4 g of NH3

Practice Problems How many grams of H2 are needed to react with an excess of nitrogen to make 25.5 grams of NH3?

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Mass-Volume Conversion Problems ___ O2 + ___ H2 ___ H2O How many liters of H2O can be produced if 25 grams of oxygen reacts with an excess of hydrogen? 1 2 2

Practice Mass-Volume Problems How many grams of hydrogen are needed to completely react with an excess of oxygen to produce 35.5 L of H2O?

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2 guards + 2 forwards + 1 center  Basketball Team *We are assuming that the team is ONLY the starting line-up Mainly because it’s easier to say “teams” over “line-ups” Interpreting Everyday Equations 2 guards + 2 forwards + 1 center  Basketball Team 2G + 2F + 1C  G2F2C How many guards does it take to make 7 teams? How many forwards are there in 8 teams? If you have 8 centers, 17 forwards and 14 guards, how many teams can be made? What position do you run out of first? 14 16 7 guards

Limiting & Excess Reagent Limiting Reagent – the reactant that runs out first! Excess Reagent – the reactant that is in abundance.

Limiting & Excess Reagent Limiting Reagent – the reactant that runs out first! Excess Reagent – the reactant that is in abundance.

Are needed for this reaction. 1 mol of N2 Limiting Reagent? ___ N2 (g) + ___ H2 (g) ___ NH3 (g) If 2.7 moles of nitrogen reacts with 6.3 moles of hydrogen, which will you run out of first? *Choose one substance to convert. Then compare to givens. 1 3 2 HAVE HAVE NEED 2.7 mol of N2 3 mol of H2 8.1 mol of H2 Are needed for this reaction. 1 mol of N2 MOLE RATIO Were we given enough moles of hydrogen for our reaction? Which reactant will run out first?

You try: 1 N2 (g) + 3 H2 (g) 2 NH3 (g) If 3.9 moles of nitrogen reacts with 12.1 moles of hydrogen, what is the limiting reagent? What would be the excess reagent? And by how much? HAVE HAVE

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Percent Yield Percent yield is a ratio that tells us how efficient a reaction is. The higher the percent yield, the more efficient a reaction Why percent yield? Predictions of a yield are not always accurate, because reactions do not always go to completion in the real world.

Percent Yield Actual Yield = the amount you experimentally get when you run a reaction in a lab. Theoretical Yield = the amount you are ideally supposed to get if everything goes perfectly. You can calculate this amount using stoichiometry. YOU ACTUALLY GOT! YOU SHOULDA GOT!

2H2 (g) + O2 (g)  2H2O (g) A student reacts 40 grams of hydrogen with an excess of oxygen, how many grams of water should he produce? If the student produced 300 grams of water, find the % yield for this reaction.

If 25 grams of oxygen reacted with an excess of hydrogen, how many grams of water should you produce? If you only produced 15 grams of water, what is the % yield for the reaction?

Exit Slip When reacting oxygen and hydrogen, you produced 50 grams of water. When by using stoichiometry, you found out you should have produced 64.5 grams of water, what is the % yield for the reaction?