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**STOICHIOMETRY Mass relationship of reactants and products in a chemical reaction**

Hydrogen gas + nitrogen gas ----> ammonia gas Qualitative: describes the “nature” of the reactants and products Quantitative: describes the amounts of reactants and products

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**Steps for solving Stoichiometry problems:**

Write a balanced equation for the question. Understand the mole and molar ratio Convert mass of reactant to moles of reactant. Convert moles of reactant to moles of product. Convert moles of product to grams of product. Pick up the calculator and do the math!!

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**How about something a little easier to follow???? Like………….**

FOOD!!!!!

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**The Stoichiometry of a sandwich…..**

The SMCHS famous sandwich consists of 2 slices of bread, 2 slices of deli meat, 1 slice of cheese, and 3 slices of pickle. Write an equation for the recipe…... 2 slices bread + 2 slices meat + 1 slice cheese + 3 slices pickle sandwich OR….. 2B + 2M + 1C + 3P B2M2CP3

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**EVALUATION: WE CAN MAKE 4 COMPLETE SANDWICHES!!**

How many SMCHS famous sandwiches can be produced when 8 slices of bread, 8 slices of meat, 4 slices of cheese, and 12 slices of pickles are available? Break it down….. BREAD: 8B = 4 B2M2CP3 MEAT: M = 4 B2M2CP3 CHEESE: 4C = 4 B2M2CP3 PICKLES: 12P = 4 B2M2CP3 EVALUATION: WE CAN MAKE 4 COMPLETE SANDWICHES!!

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**How many of each ingredient is needed to make 10 SMCHS famous sandwiches?**

BREAK IT DOWN….. BREAD: 10B2M2CP3 x (2B / B2M2CP3 )= 20B MEAT: 10B2M2CP3 x (2M / B2M2CP3 )= 20M CHEESE: 10B2M2CP3 x (1C / B2M2CP3 )= 10C PICKLES: 10B2M2CP3 x (3P / B2M2CP3 )= 30P THUS: 10 Sandwiches require 20B, 20M, 10C, and 30P

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**But what if you ran out of pickles?**

Pickles would be the LIMITING REAGENT for the sandwiches In any reaction you will likely have a limiting reagent AND an excess reagent. Too little of one Too much of the other

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**3 H2 + 1 N2 2NH3 What do the coefficients mean?**

3 molecules : 1 molecule : 2 molecules OR 3 moles : 1 mole : 2 moles

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1N2 + 3H2 2NH3 1 molecules : 3 molecules : 2 molecules 10 molecules : 30 molecules : 20 molecules 100 molecules : 300 molecules : 200 molecules 1 (6x1023) : 3 (6x1023) : 2 (6x1023) 1 MOLE : 3 MOLE : 2 MOLE

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**allowing you to solve problems dealing with masses of substances!**

1N2 + 3H2 2NH3 1mole of : 3mole of : 2mole of N2 molecules H2 molecules NH3 molecules This is the MOLAR RATIO allowing you to solve problems dealing with masses of substances!

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**1 N2 + 3 H2 2 NH3 If 75g of hydrogen reacts,**

A) How many g of N2 reacts? Use the molar ratio!! First convert the grams to moles…… 75g H2 x 1moleH2 / 2.02g H2

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**Next use molar ratio….. 75g H2 x 1mole x 1mole N2 2.02g H2 3mole H2**

Now you’ve converted to moles of N2, make the final conversion into grams!!! 75g H2 x 1mole x 1mole N2 x 28g N2 2.02g H mole H mole N2

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**75g H2 x 1mole H2 x 1mole N2 x 28g N2 2.02g H2 3mole H2 1mole N2**

= 346.5g = 350g of N2

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**1 N2 + 3 H2 2 NH3 If 75g of hydrogen reacts, B) How many g of NH3 are formed?**

75g H2 x 1mole H2 x 2mole NH 3 x g NH3 2.02g H mole H mole NH3 MOLAR RATIO: 3mole H2 : 1mole N2 : 2mole NH 3 = 420g NH3

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**Use the same system for these**

Mass - Volume Stoichiometry Instead of converting the moles of unknown to grams you convert to volume (L) Volume - Volume - Stoichiometry Instead of using the molar ratio you use volume ratio and solve for volume Rules remain the same. Just use these differences and when dealing with mass of gas STP comes in

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Can’t directly measure moles Measure units related to moles: –Mass (molar mass) –Number of particles (6.02 x 10 23 ) –Liters of gas (22.4 Liters at STP)

Can’t directly measure moles Measure units related to moles: –Mass (molar mass) –Number of particles (6.02 x 10 23 ) –Liters of gas (22.4 Liters at STP)

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