Etiket Arşivleri: STOICHIOMETRY

Intro to Stoichiometry

What is stoichiometry?

Stoichiometry is the calculation of quantitative (measurable) relationships of the reactants and products in a balanced chemical reaction (chemicals).

Material Balance With Chemical Reaction

Stoichiometry

For the chemical reaction: aA + bB → cC + dD

a,b,c,d are the Stoichiometric Coefficients, representing the molar balance of the equation. a moles of A react with b moles of B to form c moles of C and d moles of D. The stoichiometric coefficients can refer to g-moles, lb-moles, kmols, etc., but NOT g, lbm, kg or any units of mass.

So, the reaction equation DOES show:

• The reactants and products

• The molar ratios of species involved in the reaction

It DOES NOT show:

• How fast the reaction goes (Kinetics)

• How far the reaction goes (Thermodynamics, Kinetics)

• The reaction mechanism (Chemistry)

Stoichiometry of Chemical Formulas and Reactions

Stoichiometry of Chemical Formulas and Reactions

The law of definite proportions states that the element ratios for a given compound remain constant. The subscripts in a chemical formula may therefore be used to define molar ratios between the elements in the formula or between an element and the compound. For example, the chemical formula for water is H2O. Therefore, we can write

Stoichiometry of Combustion

  • FUNDAMENTALS: moles and kilomoles

  • CHEMICAL REACTIONS

  • SPECIE’S CONCENTRATIONS AND FRACTIONS

  • STOICHIOMETRY OF HYDROCARBONS OXIDATION

  • TYPES OF OXIDIZERS

  • COMPOSITION OF FUEL MIXTURE

  • TYPES OF COMBUSTIBLE MIXTURES

  • BURNING OF STOICHIOMETRIC METHANE MIXTURE IN AIR

  • BURNING OF STOICHIOMETRIC METHANE MIXTURE IN AIR: flue gas composition

  • BURNING OF LEAN METHANE MIXTURE IN AIR

  • BURNING OF LEAN METHANE MIXTURE IN AIR: flue gas composition

  • STOICHIOMETRIC AIR

  • THE STOICHIOMETRIC RATIO

  • AN EQUIVALENCE RATIO

  • AIR/FUEL RATIO (AFR) and FUEL/AIR RATIO (FAR)

  • STOICHIOMETRIC RATIO/EQUIVALENCE RATIO AND TYPE OF MIXTURE

  • AIR EXCESS

  • STOICHIOMETRIC AIR/FUEL RATIO FOR SELECTED GASES

Stoichiometry Review Practice

1. Explain the term mole ratio in your own words. When would you use this term?

 

2. Carbon disulfide is an important industrial solvent. It is prepared by the unbalanced reaction of carbon with sulfur dioxide.

C (s) + SO2 (g) –> CS2 (l) + CO (g)

a. How many moles of carbon disulfide form when 2.7 moles of carbon react?

b. How many moles of carbon are needed to reaction with 5.44 moles of sulfur dioxide?

c. How many moles of carbon monoxide form at the same time 0.246 moles of carbon disulfide forms?

d. How many moles of sulfur dioxide are required to make 118 moles of carbon disulfide?

 

3. Methanol (CH3OH) is used in the production of many chemicals. Methanol is made by reacting carbon monoxide and hydrogen at high temperature and pressure.

CO (g) + 2 H2 (g) –> CH3OH (g)

a. How many moles of each reactant are needed to produce 3.60 x 102 g methanol?

b. Calculate the number of grams of each reactant needed to produce 4.00 moles of methanol.

c. How many grams of hydrogen are necessary to react with 2.85 mol CO?

 

4. The reaction of fluorine with ammonia produces dinitrogen tetrafluoride and hydrogen fluoride.

5 F2 (g) + 2NH3 (g) –>N2F4 (g) + 6HF (g)

a. If you have 66.6g ammonia, how many grams of F2 is required for a complete reaction?

b. How many grams of ammonia are required to produce 4.65 g hydrogen fluoride?

c. How many grams of dinitrogen tetraflouride can be produced from 225g F2?

 

5. Lithium nitride reacts with water to form ammonia and aqueous lithium hydroxide.

Li3N (s) + 3 H2O (l) –> NH3 (g) + 3LiOH (aq)

a. What mass of water is needed to react with 32.9g lithium nitride?

b. When the above reaction takes place, how many molecules of ammonia are produced?

c. Calculate the number of grams of lithium nitride that must be added to an excess of water to produce 15.0 L ammonia gas at STP.

 

6. In a reaction chamber, 3.0 mol of aluminum is mixed with 5.3 mol Cl2 and reacts. The reaction is described by the following unbalanced chemical equation.

Al + Cl2 –> AlCl3

a. Identify the limiting reagent for the reaction.

b. Calculate the number of moles of product formed.

c. Calculate the number of moles of excess reagent remaining after the reaction.

 

7. Heating an ore of antimony (Sb2S3)in the presence of iron give the element antimony and iron (II) sulfide.

Sb2S3 (s) + 3Fe (s) –> 2Sb (s) + 3FeS (s)

When 15.0g Sb2S3 reacts with an excess of Fe, 9.84 g Sb is produced. What is the percent yield of this reaction?

 

8. Calcium carbonate reacts with phosphoric acid to produce calcium phosphate, carbon dioxide, and water.

3CaCO3 (s) + 2H3PO4 (aq) –> Ca3(PO4)2 (aq) + CO2 (g) + 3H2O (l)

a. How many grams of phosphoric acid react with excess calcium carbonate to produce 3.74 g calcium phosphate?

b. Calculate the number of grams of CO2 formed when 0.773g H2O is produced.

 

9. Nitric acid and zinc react to from zinc nitrate, ammonium nitrate, and water.

4Zn (s) + 10 HNO3(aq) –>4 Zn(NO3)2 (aq) + NH4NO3 (aq) + 3H2O (l)

a. How many atoms of zinc react with 1.49g nitric acid?

b. Calculate the number of grams of zinc that must react with an excess of nitric acid to form 29.1g ammonium nitrate.

 

10. Hydrazine (N2H4) is used as rocket fuel. It reacts with oxygen to form nitrogen and water.

N2H4 (l) + O2 (g) –>N2 (g) + 2H2O (l)

a. How many liters of nitrogen (at STP) from when 1.0 kg of hydrazine reacts with 1.0 kg of oxygen gas?

b. How many grams of the excess reagent remain after the reaction?

 

11. When 50.g g of silicon dioxide is heated with an excess of carbon, 32.2g of silicon carbide is produced.

SiO2 (s) + 3C (s) –> SiC (s) + 2CO (g)

a. What is the percent yield of this reaction?

b. How many grams of CO gas are made?

 

12. If the reaction below proceeds with a 96.8% yield, how many kilograms of calcium sulfate are formed when 5.24 kg of sulfur dioxide reacts with an excess of calcium carbonate and oxygen?

2CaCO3 (s) + 2SO2 (g) + O2 (g) –> 2CaSO4 (s) + 2CO2 (g)

 

13. For the reaction below there is a 100.0g of each reactant available. Which reagent is the limiting reagent?

2MnO2 + 4KOH + O2 + Cl2 –> 2KMnO4 + 2KCl + 2H2O

 

14. Explain the term heat of combustion.

 

15. When carbon disulfide is formed from its elements, heat is absorbed. Calculate the amount of heat (in kJ) absorbed when 5.66 g of carbon disulfide is formed.

C(s) + 2S(s) –>CS2 (l) ΔH = 89.3 kJ

 

16. The production of iron and carbon dioxide from iron (III) oxide and carbon monoxide is an exothermic reaction. How many kilojoules of heat are produced when 3.40mole of iron (III) oxide reacts with an excess of carbon monoxide?

Fe2O3 (s) + 3CO (g) –> 2Fe (s) + 3CO2 (g) + 26.3kJ

 

17. When 2 moles of solid magnesium combines with 1 mole of oxygen gas, 2 moles of solid magnesium oxide (MgO) is formed and 1204kJ of heat is released. Write the thermochemical equation for this combustion reaction.

 

18. Gasohol contains ethanol, C2H5OH (l), which when burned reacts with oxygen to produce carbon dioxide gas and water vapor. How much heat is released when 12.5 g ethanol burns?