Stoichiometry-Level 1 Problems

Stoichiometry

Study of the quantitative relationships that exist in chemical formulas and chemical reactions

Stoichiometry is based on what law?

Stoichiometry is based on law of conservation of mass.

mass A →→ moles A →→ moles B →→ liters B

To convert from mass of A to liters of B in a stoichiometry problem, the following steps are followed:

What 3 ideas particles and volume did Avogadro present to us?

1)Equal volumes of gas, at the same temperature and pressure contain the same number of particles.

2)Moles are numbers of particles

3)You can treat reactions as if they happen liters at a time, as long as you keep the temperature and pressure the same.

What is Avogadro's #?

6.02 x 10²³

1 mole of any element has

6.022 x 10²³ atoms

1 mole of water has

6.022 x 10²³ MOLECULES, not atoms

What is the value of 1mole in term of liter at STP?

1mole = 22.4L at STP

The balanced equation below shows the products that are formed when pentane (C₅H₁₂) is combusted.

C₅H₁₂ + 8O₂ → 10CO₂ + 6H₂O

What is the mole ratio of oxygen to pentane?

8:1

Consider the balanced equation below.

4NH₃ + 3O₂ → 2N₂ + 6H₂O

What is the mole ratio of NH₃ to N₂?

4:2 (Reduced to 2:1)

Consider the balanced equation below.

2H₂S + 3O₂ → 2SO₂ + 2H₂O

What is the mole ratio of O₂ to H₂O?

3:2

to convert grams to moles use

divide by the molar mass

#Grams / (molar mass)

to convert moles to grams

multiply by the molar mass (g/mol) of substance

#Moles x (molar mass)

How can one calculate the numbers of atoms, ions, molecules, or formula units (all different types of particles)?

multiply by Avogadro's number: 6.02 x 10²³

mol x (6.02 x 10²³ atoms or molecules/ 1 mol)

to convert number of atoms, ions, molecules, or formula units to moles

divide by Avogadro's number: 6.022 x 10²³ atoms or molecules

#Atoms x (1 mol / 6.02 x 10²³ atoms or molecules)

to convert number of atoms or molecules to mass

divide by Avogadro's number (6.022 x 10²³) and then multiply by the molar mass (g/mol) of substance

#Atoms x (1 mol / 6.02 x 10²³ atoms or molecules) x (molar mass)

to convert mass to number of atoms or molecules

divide by the molar mass (g/mol) of substance and then multiply by Avogadro's number (6.022 x 10²³)

#Grams/(molar mass) x (6.02 x 10²³ atoms or molecules / 1 mol)

To convert from molecules (particles) to grams

divide by 6.02 x 10²³ and then multiply by the molar mass of the substance.

To convert from moles to liters (of a gas)

multiply by molar volume (22.4)

mol x (22.4 L / 1 mol)

To convert form liters (of a gas) to moles

divide by molar volume (22.4)

Liters x (1 mole/ 22.4 liters)

temperature; STP

In mass-volume and volume-mass calculations, all gases are considered to be at standard

_________ and pressure, also referred to as

________

To convert from molecules (of a gas) to liters

divide by 6.02x10²³ and then multiply by 22.4

Calculate the mass, in grams, of 202 atoms of iron, Fe (1 mol of Fe has a mass of 55.85 g).

Solution: The following solution may contain one or more values that are different from the problem provided to you, however, the steps to solve the problem are the same.

The mass of a substance can be calculated from its number of atoms using Avogadro's number and its molar mass.

(202 atoms of Fe) X ((1 mol Fe) / (6.022 × 10²³ atoms Fe)) X ((55.85 g Fe) / (1 mol Fe) = 1.8 x 10⁻²⁰ g Fe

A cereal contains 11.0 grams of sucrose (C₁₂H₂₂0₁₁) per 60.0 grams of cereal. How many grams of cereal must be eaten to consume 0.0424 moles of sucrose?

Solution: (0.0424 mol C₁₂2H₂₂0₁₁) X (342.34 g C₁₂2H₂₂0₁₁) / (1 mol C₁₂2H₂₂0₁₁)) X (60.0 g cereal) / (11.0 g C₁₂2H₂₂0₁₁) = 79.2 g cereal

Determine the number of atoms in 51.0 grams of sodium, Na. (The mass of one mole of sodium is 22.99 g.)

Solution: The following solution may contain one or more values that are different from the problem provided to you, however, the steps to solve the problem are the same.

The number of atoms of a substance can be calculated using Avogadro's number and its molar mass.

(51.0 g Na) X ((1 mol Na) / (22.99 g Na) X (6.022 x 1023 atoms) X (1 mol Na)

= 1.34 × 10^24 atoms

The study of mass relationships of elements in compounds is known as...

Composition stoichiometry

The study of mass relationships amount reactants and products in a chemical reaction is known as...

Reaction stoichiometry

A balanced chemical equation allows one to determine the what?

Mole ratio of any two substances in the reaction

The coefficients in a chemical equation represent the...

Relative numbers of moles of reactants and products

write Mole ratios for

4 Al + 3O₂ → 2Al₂O₃

4 mole Al formed 2 Mole Al₂O₃( 4:2)

3 mole O₂ formed 2 mole of Al₂O₃(3:2)

MOLE TO MOLE CONVERSIONS:

How many moles of O₂ are produced when 3.34 moles of Al₂O₃ decomposed?

2Al₂O₃ → 4Al + 3O₂

1)Mole to mole ratio: 2mole Al₂O₃ to 3mole O₂

2)3.34mole Al₂O₃x(3 mole O₂/2 mole Al₂O₃)=5.01 mole O₂

MOLE TO MASS CALCULATIONS:

Determine the mass of NaCl produced when 1.25 mol of Chlorine gas reacts with Na?

2Na + Cl₂ → 2NaCl

1.25 mol Cl₂ x(2 mol NaCl/1 mol Cl₂) X (58.44g NaCl/1 mol) = 146 g NaCl.

Stoichiometric MASS TO MASS

6.50 gram of aluminum reacts with Oxygen gas. How many gram of aluminum oxide are formed?

4Al + 3O2 => 2Al₂O₃

6.50 gram Al x(1mol Al/26.98 g Al) x (2 mol Al₂O₃/4 mol Al) x (101.96 gram Al₂O₃/1mol Al₂O₃) = 12.3 gram Al₂O₃ are formed.

Volume to Volume calculation

How many liters of CH₄ at STP are required to completely react with 17.5 L of O₂ ?

CH₄ + 2O₂ → CO₂ + 2H₂O

17.5 L O₂ (1mol O₂/22/4 L O₂)(1mol CH4/2 mol O₂)(22.4 L CH₄/1 mol CH₄) = 8.75 L CH₄

or

17.5 L O₂(1L CH₄/2 L O₂)= 8.75 L CH₄

Mass and Atoms are ALWAYS conserved, however do Molecules, Formula units, moles and volumes are also always necessary be conserved?

No, The Molecules, Formula units, Moles and Volumes are not always necessary be conserved.

given the balanced equation...

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

which ratio of oxygen to propane is correct

5 moles of O₂/1 mole C₃H₈

In the chemical reaction represented by the equation wA + xB → yC + zD, a comparison of the number of moles of A to the number of moles of C would be a(n)

mole ratio.

Volume Reactants: 1 (22.4 L) N₂ + 3 (22.4 L) mol H₂

Volume Products: 2 (22.4 L) NH₃

Total Moles: 6

Question: N₂(g) + 3H₂(g) → 2NH₃(g)

Express the reactants and products in terms of volume in liters at STP conditions. Calculate the sum total of all moles in the balanced equation.

Known Amount: 75.0 L N₂

Conversion Factor: 2 (22.4 L) NH₃ / 3 (22.4 L) H₂

Unknown Amount: 50.0 L NH₃

Question: N₂(g) + 3H₂(g) → 2NH₃(g)

If 75.0 L of hydrogen is used in the reaction, how many liters of NH₃ will be produced?

Volume Reactants: 1 (22.4L) H₂ + 1 (22.4 L) Cl₂

Volume Products: 2 (22.4 L) HCl

Total Moles: 4

Question: H₂(g) + Cl₂(g) → 2 HCl(g)

Express the reactants and products in terms of volume in liters at STP conditions. Calculate the sum total of all moles in the balanced equation.

Known Amount: 12.5 L Cl₂

Mole Ratio: 2 (22.4 L) HCl / 1 (22.4 L) Cl₂

Unknown Amount: 25.0 L HCl

Question: H₂(g) + Cl₂(g) → 2 HCl(g)

How many liters of hydrogen chloride is produced if 12.5 liters of chlorine is used in the the reaction?

Volume Reactants: 2 (22.4 L) C₂H₆ + 7 (22.4 L) O₂

Volume Products: 4 (22.4 L) CO₂ + 6 (22.4 L) H₂O

Total Moles: 19

Question:

2C₂H₆(g) + 7O₂ (g) → 4CO₂(g) + 6H₂O(g)

Express the reactants and products in terms of volume in liters at STP conditions. Calculate the sum total of all moles in the balanced equation.

Known Amount: 16.2 L C₂H₆

Mole Ratio: 6 (22.4 L) H₂O / 2 (22.4 L) C₂H₆

Unknown Amount: 48.6 L H₂O

Question:

2C₂H₆(g) + 7O₂ (g) → 4CO₂(g) + 6H₂O(g)

What volume of of water vapor is formed when 16.2 L of ethane (C₂H₆) are burned in the reaction?

Volume Reactants: 2 (22.4 L) H₂ + 1 (22.4 L) O₂

Volume Products: 2 (22.4 L) H₂O

Total Moles: 5

Question: 2

2H₂(g) + O₂(g) → 2H₂O(g)

Express the reactants and products in terms of volume in liters at STP conditions. Calculate the sum total of all moles in the balanced equation.

Known Amount: 45.50 mL H₂

Conversion Factor: 1 (22400 mL) O₂ / 2 (22400 mL) H₂

Unknown Amount: 22.75 mL O₂

Question: 2

2H₂(g) + O₂(g) → 2H₂O(g)

If 45.50 mL of hydrogen are used in the reaction, how many milliliters of oxygen are needed?

Volume Reactants: 2 (22.4 L) CO + 1 (22.4 L) O₂

Volume Products: 2 (22.4 L) CO₂

Total Moles: 5

Question:

2CO(g) + O₂(g) → 2 CO₂g)

Express the reactants and products in terms of volume in liters at STP conditions. Calculate the sum total of all moles in the balanced equation.

Known Amount: 175.0 L O₂

Conversion Factor: 2 (22.4 L) CO₂ / 1 (22.4 L) O₂

Unknown Amount: 300.0 L CO₂

Question:

2CO(g) + O₂(g) → 2 CO₂g)

If 175.0 L of oxygen are used in the reaction, how much carbon dioxide in liters will be produced?

Ammonia is formed by the reaction of nitrogen with hydrogen.

N₂(g)+3H₂(g)→2NH₃(g)

If you want to produce 100.0 g of ammonia what mass of hydrogen gas would you need?

17.75 g

Ammonia is formed by the reaction of nitrogen with hydrogen.

N₂(g)+3H₂(g)→2NH₃(g)

If you want to produce 40.0 g of ammonia what mass of nitrogen gas would you need?

32.9 g

When 300.0 g of sodium metal reacts with excess hydrochloric acid, according to the following equation, what mass of hydrogen gas is released?

2Na(s) + 2HCl(aq) → 2NaCl(aq) + H₂(g)

13.35 g

When 400.0 g of zinc metal reacts with excess hydrochloric acid, according to the following equation, what mass of hydrogen gas is released?

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

12.33 g

When an unknown mass of aluminum metal reacts with excess hydrochloric acid, according to the following equation, 1.200 g of hydrogen gas is released?

2Al(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂(g)

What mass of Aluminum must have been used?

10.71 g

When 100.0 g of aluminum metal reacts with excess hydrochloric acid, according to the following equation, what mass of hydrogen gas is released?

2Al(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂(g)

11.21 g

When an unknown mass of aluminum metal reacts with excess sulfuric acid, according to the following equation, 1.00 g of hydrogen gas is released?

4Al(s) + 6H₂SO₄(aq) → 2Al₂(SO₄)₃ (aq) + 6H₂(g)

What mass of aluminum must have been used?

8.92 g

Nitrogen dioxide reacts with water to produce nitric acid and nitrogen monoxide according to following equation:

3NO₂(g) + H₂O(l) → 2HNO₃(aq) + NO(g)

What mass of HNO₃ will be produced when 19.00 g of NO₂ is consumed in the reaction above?

17.35 g

Pure iron metal can be extracted from iron(III) oxide by reacting it with carbon monoxide according to the following balanced equation.

Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)

If 15.00 g of carbon monoxide is added to excess iron(III) oxide what mass of iron will be produced?

19.93 g

Pure iron metal can be extracted from iron(III) oxide by reacting it with carbon monoxide according to the following balanced equation.

Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)

If 29.00 g of iron(III) oxide is present how many gams of carbon monoxide are required to turn it all into iron metal?

15.26 g

Ammonia reacts with oxygen to produce nitrogen monoxide gas and water.

4NH₃ (g) + 5O₂ (g) → 4NO (g) + 6H₂O (l)

If 8.000 g of ammonia gas (NH₃) is available, how many grams of oxygen gas is required to react with all the ammonia?

18.79 g

10.1 L

In

CaCO₃ + HCl → CaCl₂ + H₂O + CO₂,

how many liters of carbon dioxide gas, measured at STP, can be obtained from 45.0 g of calcium carbonate?

1.5 mol N₂ gas

Ammonia and copper oxide react to form copper, water and nitrogen as shown in the following reaction:

2NH₃(g) + 3CuO(s) → 3Cu(s) + 3H₂O(l) + N₂(g)

If a sample of 51 g of ammonia was reacted with excess copper oxide, how many moles of nitrogen would be produced?

0.51 g

The reaction below shows the decomposition of sodium azide into sodium metal and nitrogen gas.

2NaN₃(s) → 2Na(s) + 3N₂(g)

An unknown amount of sodium azide (NaN₃) reacts and produces 0.033 moles of nitrogen gas. What mass of sodium metal is produced?

67.2 L N₂

Use the reaction below for the decomposition of sodium azide to sodium metal and nitrogen gas.

2NaN₃(s) → 2Na(s) + 3N₂(g)

What volume of nitrogen at STP is generated by the decomposition of 130. g NaN₃?

160. g CH₃OH

Use the reaction below for the combustion of methanol.

2CH₃OH(l) + 3O₂(g) → 2CO₂(g) + 4H₂O(l)

What mass of methanol is combusted in a reaction that produces 112 L of CO₂ at STP?