16.5 Solving Equilibrium Problems--A Different Way of Thinking

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Precipitation Reactions Two versions of the Orange Tornado, two reactions under a microscope, and updated stills of other precipitation reactions provide dramatic visual displays of solid formation.

Equilibrium : CalcRxnQuotient (13 Variations) In an experiment, 4.44 mol of SO_{2}, 7.93 mol of O_{2} and 4.03 mol of SO_{3} are placed in a 2.0L reaction vessel at a certain temperature. Calculate the reaction quotient, Q, for the reaction as written:

What is the calculated reaction quotient, Q? {2:NUMERICAL:=2.1e-1:1e-2#Correct! ~%50%2.1e-1:5e-2#Close but not quite right}

If K_{c} for this reaction at the temperature of the experiment is 3.7 x 10^{3}, will the reaction move toward the left or toward the right? {1:MULTICHOICE:left#Sorry, that's wrong.~=right#Correct!}

If you have 1.00 mole of COCl_{2}(g) in a 1.00L container initially, how many moles of COCl_{2} will be present when the system reaches equilibrium?

Equilibrium |

Chemometrics

Equilibrium : CommonIonEffect (9 Variations)
The molar solubility of lead(II) fluoride (PbF_{2}) is
2.1 x 10^{-3} mol/L in pure water at 25^{o}C. What is the molar solubility of lead(II) fluoride in 0.10 M NaF at 25^{o}C? (Assume that the only relevant reaction is the solubility-product equilibrium.)

The Reaction Quotient Is Unnecessary To Solve Equilibrium ProblemsPaul S. Matsumoto The traditional method to determine the equilibrium concentration of chemicals in a reaction, given the equilibrium constant and the initial concentration of chemicals in the reaction, involves the determination of the reaction quotient. This article will demonstrate that this step may be eliminated; thereby simplifying the algorithm to solve such problems. Such a reduction in the complexity of the algorithm may result in more students successfully being able to solve such problems. Matsumoto, Paul S. J. Chem. Educ.2005, 82, 406.

Equilibrium |

Learning Theories |

Chemometrics

Unified Approximations: A New Approach for Monoprotic Weak Acid–Base EquilibriaHarry L. Pardue, Ihab N. Odeh, and Teweldemedhin M. Tesfai This article describes a new approach to approximate calculations for monoprotic acidbase equilibria in otherwise pure water. The new approach, identified herein as unified approximations, uses a simple decision criterion to select between situations that should be treated as deprotonation and protonation reactions. The remaining treatment takes account of changes in concentrations of conjugate acidbase pairs for all situations and ignores autoprotolysis only for situations for which the analytical concentration of either the conjugate acid or conjugate base will always be larger than zero. Pardue, Harry L.; Odeh, Ihab N.; Tesfai, Teweldemedhin M. J. Chem. Educ.2004, 81, 1367.

Acids / Bases |

Equilibrium |

Chemometrics

Reaction to Why Do We Teach Equilibrium Calculations?Stephen J. Hawkes "Rigor" in introductory chemistry is often equated with quantitation. Consequently the understanding of chemical reactions and properties is obscured. This was illustrated by Stumpo who asked students to calculate ?E of a reaction, and then on another question on the same test asked a question aimed at its meaning. 77% of the students calculated correctly, but only 24% showed understanding of its meaning. The ability to calculate a number does not measure understanding of the number. Hawkes, Stephen J. J. Chem. Educ.2004, 81, 1265.

EquilibriumMatthew Sandberg, Mike Bellamy Using a visual approach, this applet is designed to help students learn to solve equilibrium calculations and also to help them gain a deeper understanding of the topic. It can be used by the instructor in the classroom as equilibrium topics are introduced. Sample exercises for students are included. The text is available in both English and Spanish.

Chemometrics |

Equilibrium |

Enrichment / Review Materials

JavaScript Programs To Calculate Thermodynamic Properties Using Cubic Equations of StatePatrick J. Barrie Cubic equations of state are widely used by chemists and chemical engineers to predict the thermodynamic properties of both pure substances and mixtures. In particular, these equations enable predictions concerning the temperature and pressure at which vapor liquid equilibrium occurs. These two educational JavaScript programs perform calculations using cubic equations of state and, equally importantly, explain how the calculations are performed.

Mathematics / Symbolic Mathematics |

Chemometrics |

Thermodynamics |

Equilibrium |

Enrichment / Review Materials

The Equilibrium ConstantEd Vitz, John W. Moore A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.