STOICHIOMETRY

STEPS

100

What is the first step you take when doing stoichiometry?

Write the balanced equation.

200

If you are given moles of a substance, and you are trying to calculate moles required of another substance, what do you use for this calculation?

mol:mol ratio

300

If you are given grams of a substance, and you are trying to calculate the grams required of another substance, what do you do after writing the balanced chemical equation?

convert grams to moles

400

How do you know when the question requires us to calculate the limiting reagent?  Do NOT write "when the question tells you to"

When you are given 2 amounts for substances - the amounts of both reactants

500

Write out the steps that you would do for this question (DO NOT calculate): Hydrogen gas and oxygen gas react in a synthesis reaction to create water.  If you have 50 g of hydrogen gas, how much water will form?

1) Write a balanced chemical equation

2) Convert g of hydrogen gas to moles

3) Use mol:mol ratio to covert to moles of water

4) Convert moles of water to grams

CONVERSIONS

100

How many moles of Fe₂O₃ will form from 5.0 moles of Fe?

Fe_(s) + O_2(g) -> Fe₂O_3(s)

n = 2.5 moles of Fe₂O₃

200

How many molecules of magnesium oxide will form when excess magnesium reacts with 480 molecules of oxygen? 

Mg_(s) + O_2(g) -> MgO_(s)

N = 960 molecules of MgO

300

How many moles of KClO₃ must decompose in order to produce 9 moles of oxygen gas?

n = 6 moles KClO₃

400

When silicon oxide reacts with hydrofluoric acid, silicon fluoride and water form. In the reaction, 7.42 mol of each reactant is used.

a.   Write and balance the chemical equation for the reaction.

b.   Determine which is the limiting reactant.

a. SiO_2(s) + 4HF_(aq) -> SiF_4(g) + 2H₂O_(l)

b.  hydrofluoric acid is the limiting reagent

500

In the single displacement reaction of solid copper and silver nitrate, 4.75 g of solid copper and 8.16 g of silver nitrate are used. Which is the limiting reactant?

silver nitrate

DEFINITIONS

100

What do we look at to find mole ratios?

The coefficients in a balanced equation.

200

What is Actual Yield?

Actual amount of a product that can be formed (in a lab) using up the limiting reactant.

300

What is a Theoretical Yield?

The maximum amount of a product that can be produced - based on stoichiometry calculations.

400

What is Excess Reactant?

Reactant that is not used up when a reaction is run to completion.

500

What factors affect the actual yield (making it lower than the theoretical yield)?

1) Competing reactions

2) Reaction rate

3) Impure or diluted reactants

4) Lab technique

MOLE RATIOS

100

Fe + O₂--> Fe₂O₃

Find the mole ratio of Iron to Oxygen

4:3

200

In the reaction of ammonia gas with oxygen, nitrogen dioxide gas and water are formed.

a.   Write and balance the chemical reaction for this process, including the states of matter

b.   What is the mole ratio between oxygen and water?

a.   4NH_3(g) + 7O_2(g) -> 4NO_2(g) + 6H₂O_(l)

b.   oxygen and water = 7 : 6

300

In the decomposition reaction of ammonium nitrate, nitrogen gas, oxygen gas, and water form.

a.   Write and balance the chemical equation for this process.

b.   What is the mole ratio between ammonium nitrate and nitrogen gas?

a.  2NH₄NO_3(aq) -> 2N_2(g) + O_2(g) + 4H₂O_(l)

b.  1:1

400

a.   Balance the following chemical equation:

MoS_2(S) + O_2(g) -> MoO_3(s) + SO_2(g)

b.   What amount (in moles) of sulfur dioxide will be produced if 227.85 mol of oxygen are used in the process?

a. 2,7,2,4

b. 130.20 mol

500

a.   Balance the following chemical equation:

NH₄Cl_(aq) + Ca(OH)_2(aq) -> NH_3(g) + H₂O_(l) + CaCl_2(aq) 

b.   What amount (in moles) of water will be produced if 7.68 mol of calcium hydroxide is used in the process?

a.  2,1,2,2,1

b. 15.36 mol

STOICH PROBLEMS

100

Fe₃O₄ + 4 CO--->3 Fe + 4 CO₂

How many moles of CO are needed to react with 

16.5 g of Fe₃O₄?

n = 0.285 moles CO

200

How many grams of NaCl will be produced from 1.25 mol of chlorine gas reacting with sodium?

Na_(s) + Cl_2(g) -> NaCl_(s)

m = 146 g of NaCl

300

Ammonium nitrate decomposes into dinitrogen monoxide gas and water. Determine the amount in grams of water produced if 25.0 g of ammonium nitrate decomposes.

m = 11.3grams H₂O

400

Solid sodium and chlorine gas react to form sodium chloride according to the reaction. 

Na_(s) + Cl_2(g) -> NaCl_(s)

If 200.00 g of each reactant is used, what is the limiting reagent?  What mass of product will form?

Limiting reagent = Cl₂

m = 329.6 g NaCl

500

In the decomposition of mercury(II) oxide, liquid mercury and oxygen gas form.

a.   Write and balance the chemical equation.

b.   Determine the mass of liquid mercury that will form if 1.62 mol of mercury(II) oxide are used.

c.   If 295.73 g of mercury actually form, what is the percentage yield?

m = 324.96g of liquid Hg

91% yield