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# Making Connections in Kinetics, Equilibrium and Thermochemistry (8 Favorites)

LESSON PLAN in Catalysts, Entropy, Equilibrium Constants, Enthalpy, Activation Energy, Energy Diagrams, Reaction Quotient, Spontaneous vs. Non-spontaneous Reactions. Last updated October 19, 2018.

### Summary

In this lesson students will understand the connections between the equilibrium constant (K) and the reaction quotient (Q) as well as how they determine the favorability of a reaction. Additionally students will be able to determine if a reaction is kinetically favored or thermodynamically favored.

### Grade Level

High School (AP Chemistry)

### AP Chemistry Curriculum Framework

The laws of thermodynamics describe the essential role of energy and explain and predict the direction of changes in matter.__Big Idea 5:__**5.18**The student can explain why a thermodynamically favored chemical reaction may not produce large amounts of product (based on consideration of both initial conditions and kinetic effects), or why a thermodynamically unfavored chemical reaction can produce large amounts of product for certain sets of initial conditions.

__Big Idea 6:__**6.25**The student is able to express the equilibrium constant in terms of Δ*G*and^{o}*RT*and use this relationship to estimate the magnitude of*K*and, consequently, the thermodynamic favorability of the process.

### Objectives

By the end of this lesson, students should be able to

- Use K vs. Q to determine the direction a reaction proceeds.
- Understand how equilibrium relates to favorability of a reaction.
- Determine the favorability of a reaction based upon kinetics and thermochemistry.

### Chemistry Topics

This lesson supports students’ understanding of

- Equilibrium
- Equilibrium Constant
- Reaction Quotient
- Kinetics
- Activation Energy
- Catalysts
- Thermodynamic Favorability
- Energy Diagrams
- Enthalpy
- Entropy
- Spontaneity
- Free Energy

### Time

**Teacher Preparation**: 30 minutes (Preparing and practicing the demonstration)

**Lesson**: Activity: 60-90 minutes

Demo: 30 minutes including discussion

### Materials

- Demo Materials
- 30%
H
_{2}O_{2}(50 mL per demo) - MnO
_{2 }solid (a few grams per demo–exact amount not required) - 250 mL volumetric flask
- 50 or 100 mL graduated cylinder (to measure peroxide solution)
- Scoopula or spoon to obtain solid catalyst
- Flinn Disposal #26 is a disposal option. (*If you do not have a Flinn Reference Catalog please order a free copy.)

### Safety

- Always wear safety goggles when handling chemicals in the lab.
- Students should wash their hands thoroughly before leaving the lab.
- Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
- 30% Hydrogen Peroxide is a strong oxidizer, please read the safety sheet prior to handling this chemical.
- Wear gloves when using 30% Hydrogen Peroxide.

### Teacher Notes

- This lesson is intended to help students make connections between the following concepts: equilibrium, thermochemistry and kinetics. The students should have knowledge of general equilibrium, kinetics, catalysts, enthalpy and entropy before completing the activity.

__Lesson Outline:__

- The demonstration should follow the Guided Inquiry Activity as a formative assessment of the students understanding of the lesson.
__Guided Inquiry Activity__*: Determining Reaction Favorability*(student handout provided). Randomly divide students into teams of 2-4. Students should work through this activity together and divide the work among the members as noted in the activity.- An Answer Key document has been provided for teacher reference.
- After the groups have finished, discuss the answers and be certain all questions have been addressed.
__Demo__:*Catalyzed decomposition of hydrogen peroxide using manganese dioxide.*__*Note__:*ALWAYS practice a demonstration prior to attempting in front of students.*- Video of Demonstration for reference.
- Procedure:

- Introduce
the demo by drawing the potential energy diagram for H
_{2}O_{2}without a catalyst on the board.

*Graph Created by author

- Ask the students “What is the sign of ∆H? Why?”
- Confirm the student’s choice.
**Answer: the sign of ∆H is negative, the products are lower in energy than the reactants so energy is released.** - Pour some (50 mL) hydrogen peroxide (30% preferred) in a 250 mL volumetric flask.
- Ask the students “What do you observe?”
**Answer: students may observe some small bubbles, the solution is clear.** - Ask the students “What is the sign of ∆S? Why?
- Confirm the student’s choice.
**Answer: the sign of ∆S is positive, the reactants include one aqueous solution and the products contain liquid water and oxygen gas, disorder increases.** - Ask the students “Considering the sign of ∆H and of ∆S, predict the sign of ∆G, why?”
- Confirm the student’s choice.
**Answer: the sign of ∆H is negative and the sign of ∆S is positive which means the sign of ∆G is negative at all temperatures.** - Ask the students “Considering the sign of ∆G is negative, what does this indicate about the thermodynamic favorability of this reaction?”
- Students should say
**“thermodynamically favorable”** - Ask the students “If this reaction is thermodynamically favorable, why do we not see a reaction taking place?”
- Students should say things like
**“it is slow, has a high activation energy, needs a catalyst, etc.** - Introduce the Manganese Dioxide catalyst to the students and ask “what will adding the catalyst do to the graph on the board?
- Confirm the student’s choice by adding the catalyst line on the graph lowering the activation energy.

*Graph Created by Christine Taylor

- Slowly add a small scoop of MnO
_{2}to the H_{2}O_{2}in the volumetric flask. - The reaction will quickly occur decomposing the hydrogen peroxide and releasing copious amounts of water vapor, oxygen gas and heat.
- Ask the students “Do you think this reaction is under thermodynamic or kinetic control?”
- Confirm the student’s choice. Answer: Due to the high activation energy and the fact that the reaction is spontaneous but does not visibly occur without a catalyst, the reaction is under kinetic control.

- Additional Resource Suggestions:
- Try this Predicting Shifts in Equilibrium Quiz with students from AACT.
- Use this Free Energy and Temperature simulation to reinforce concepts (flash needed).