Unit 1. Stoichiometry and Reaction Progress

This website provides learning and teaching tools for a first course on kinetics and reaction engineering. The course is divided into four parts (I through IV). Here, in Part I of the course, a brief review of some basic concepts related to chemical reactions is presented. Students taking their first kinetics and reaction engineering course should already be familiar with most of the material that is presented in this part of the course. The concepts that are reviewed here will be utilized repeatedly throughout the remainder of the course, and therefore it is critically important to master them before proceeding to the main body of the course, Parts II, III and IV.

Unit 1 reviews some basic concepts related to chemical reactions. The first topic is reaction stoichiometry, and it includes the sign convention for stoichiometric coefficients that will be used throughout this course. The remainder of the unit reviews how stoichiometry can be used when calculating the composition of a reacting system as the reaction or reactions proceed. In doing so, some common reaction progress variables are introduced and defined.

Learning Resources

• Archive (.zip) - Contains all learning resources listed below for this unit
• Documents to Read:
  • Unit 01 Informational Reading (.pdf)
  • Example 1.1 (.pdf)
  • Example 1.2 (.pdf)
  • Example 1.3 (.pdf)
  • Example 1.4 (.pdf)
• Videos to Watch (please right-click and save, then play back locally on your computer):
  • Unit 01 Informational Video (.mov)
  • Example 1.1 Video (.mov)
  • Example 1.2 Video (.mov)
  • Example 1.3 Video (.mov)
  • Example 1.4 Video (.mov)
• Reference Files:
  • Unit 1 Definitions, Nomenclature and Equations (.pdf)
  • Identifying and Thinking Through Reaction Progress Problems
  • How To Solve Stoichiometry Problems (.pdf)
  • How To Express C_A in Terms of n_B, (.pdf) for a single reaction system.
• Other Files:
  • Example_1_4.m - modified version of SolvNonDif.m (see Supplemental Unit S2) that was used in the solution of Example 1.4

Teaching Resources

• Archive (.zip) - Contains all teaching resources listed below for this unit
• Sample Class
  • Online Pre-class Quiz (.pdf file)
  • Redacted slides to make available to students before class
    • Keynote 09
    • PowerPoint
  • Learning Activity Files to make available to students before class
    • Activity 1 Worksheet (.pdf) - to the in-class activity problems
  • Class Lesson Plan (.pdf)
  • Complete slides to make available to students after class
    • Keynote 09
    • PowerPoint
  • Learning Activity Files to make available to students after class
    • Activity 1 Solutions (.pdf) - to the in-class activity problems
• Alternative Questions (.pdf) that could be used in a pre-class quiz
• Alternative In-Class Learning Activities
  • Alternative Activity 1.1 (.zip) - an activity where the students will draw upon their own life experiences to illustrate, by analogy, the primary focus of kinetics, thermodynamics and reaction engineering and the inter-relationships between them.
  • Alternative Activity 1.2 (.zip) - an activity where the students will use physical models of molecules to explore the origins of reaction stoichiometry.
  • Alternative Activity 1.3 (.zip) - an activity where the students will work in groups to prepare a three slide presentation describing how to find a complete mathematically independent sub-set of a group of reactions.
  • Alternative Activity 1.4 (.zip) - an activity where the students will “explore and learn” about reaction progress variables individually or in a group.

Practice Problems

1. Cellulosic biomass is a renewable resource that could be used for the production of fuels and chemicals. Suppose that the nominal chemical formula for cellulose is C₆H₁₀O₅ and write a balanced chemical reaction for the steam gasification of cellulose to produce carbon monoxide and hydrogen (H₂). List the values of the four stoichiometric coefficients that appear in the reaction. (Problem Statement as .pdf file)

2. Several words and phrases from Unit 1 are hidden in this puzzle (.pdf). The words may appear right to left, left to right, top to bottom, bottom to top or in either direction along a diagonal. Find as many terms as you can and write a brief definition for each one you find. There are at least 19 items, along with a few bonuses, hidden in the puzzle. (Problem Statement as .pdf file)

3. In the gasification of cellulosic biomass (here represented using its nominal formula, C₆H₁₀O₅), the carbon from the cellulose could be released either as CO (see Practice Problem 1), or as CO₂, reaction (3a). In addition, the water-gas shift, reaction (3b), can lead to a mixture of CO and CO₂. Suppose a reaction began with 10 moles of H₂O for every one mole of C₆H₁₀O₅, and no other species present. If half of the cellulose is consumed and the products contain 3 moles of CO₂ for every mole of CO, what will the ratio of CO to H₂ equal?

(Problem Statement as .pdf file)

4. The gas phase reaction 2 NO + 5 H₂ → 2 NH₃ + 2 H₂O takes place in a system that initially contained 2 moles of H₂ and 1 mole of NO. If 50% of the limiting reagent is converted, what will the mole fraction of ammonia equal? (Problem Statement as .pdf file)

5*. A graduate student was studying the gas phase decomposition of N₂O according to reaction (5a). The student ran several experiments involving this reaction using a steady-state flow reactor. The feed to the reactor always contained a mixture of helium and nitrous oxide (neither oxygen nor nitrogen was ever used in the feed), and the total pressure was 1 atm in each experiment. The inlet flow rates and the reactor temperature were held constant in each individual experiment. A gas chromatograph was used to measure the composition of the gas leaving the reactor. Using the data from the gas chromatograph, the student was easily able to calculate the mole fraction of oxygen leaving the reactor. Use the experimental data provided in the table below (or as an Excel file here) to calculate the outlet concentrations of N₂O, N₂ and O₂ for each of the student's experiments.

(Problem Statement as .pdf file)

6. Steam reforming of methane, reaction (6a) is used commercially to manufacture hydrogen. Suppose a 10 L reactor initially contains a gas mixture with 70% steam and 30% methane at 2 atm and 375 °C. Assuming reaction (6a) is the only reaction that takes place and that the temperature is constant, (a) calculate the final concentration of hydrogen if 95% of the methane is converted. (b) Derive an expression (valid at any conversion) for the concentration of steam in terms of the reactor volume, the initial moles of steam, the initial moles of methane and the final moles of methane.

(Problem Statement as .pdf file)

7. Suppose that a flow reactor operates isothermally at 800 K and 3 atm where ideal gas behavior can be assumed. A gas mixture at 800 K and 3 atm containing 90% N₂, 8% O₂ and 2% NH₃ by volume flows into the reactor at a rate of 4 L min^-1 and reacts according to reaction (7a).

(a) If this reactor was being used to generate kinetics data, it might be necessary to write an expression for the outlet partial pressure of ammonia in terms of known constants and the outlet molar flow rate of ammonia in order to analyze the data. In doing so, it is important to recognize that the total outlet molar flow rate will change when the outlet molar flow rate of ammonia changes. Write the expression for the outlet partial pressure of ammonia in terms of known constants and the outlet molar flow rate of ammonia.

(Problem Statement as .pdf file)