We're going to be honest: we do Physics. That's why this is called The Physics Classroom website. And when we do the Teacher's Notes section for our Concept Builders, we typically have a lot to say ... and a lot of resources to point you to. We're not claiming to be ignorant of chemistry; we just don't have a lot of resources here at The Physics Classroom to point you to. And so this page is going to be a lot shorter than our usual page that accompanies our Physics Concept Builders. That's our honest confession.

Most Chemistry courses have a unit on the topic of reversible reaction systems and chemical equilibrium. A common topic in such a unit is LeChatelier's Principle. The learning outcome is typically centered around student ability to predict the effect of a stress upon the reversible system. Stresses include and addition or removal of aqueous-state or gas-state reactant and product and increased and decreases in volume, pressure, and temperature. This Concept Builder addresses such a learning outcome through three scaffolded activities. The activities vary difficulty as one progresses from the first to the second to the third. The three difficulty levels are differentiated as follows:
 

• Apprentice Difficulty Level: Question Groups 1-4 ... The chemical equation for a reversible system is given. A particular stress is identified; the stress will either be the addition or removal of a gaseous- or aqueous-state reactant or product. Learners must identify the direction that the equilibrium will shift in response to the stress.
• Master Difficulty Level: Question Groups 5-12 ... The chemical equation for a reversible system is given. A particular stress is identified. The stress will either be the addition or removal of a reactant or product or an increase or a decrease in the pressure or temperature. Learners must identify the direction that the equilibrium will shift in response to the stress.
• Wizard Difficulty Level: Question Groups 13-18 ... The chemical equation for a reversible system is given. A particular stress is identified. The stress will either be the addition or removal of a gaseous- or aqueous-state reactant or product or an increase or a decrease in the pressure or temperature. Learners must identify the direction that the equilibrium will shift in response to the stress. They must also idenitfy how this shift will affect the amount of a particular reactant or product present in the system.

Teachers are encouraged to view the questions in order to judge which difficulty levels are most appropriate for their classes. The three difficulty levels are scaffolded such that doing all three in order makes for an effective learning experience. The levels become progressively more difficult, both in terms of the number of questions and in the difficulty of the questions themselves. For instance, the Apprentice Difficulty Level restricts all questions to the addition or removal of reactant or product. The reactants and products are all gas- or aqueous-state substances. In the Master Difficulty Level, there are three Question Groups in which a change does not result in a shift of the equilibrium. Students will have to be insightful enough to know under what conditions a change will result in a disturbance of the equilibrium. And finally, the Wizard Difficulty Level has less questions but each question includes three parts. The additional parts demand that students recognize what a shift will do to the amounts of reactants and products as the system approaches a new equilibrium position. The questions can be viewed on a separate page. 

There are three similar questions in every Question Group; the similarity has to do with the type of stress - for instance, the addition of reactant. If a student misses a question from within a particular Question Group, then they will have to answer two different questions correctly (without any further miss) from that same Question Group. This strategy provides students extra practice on their most troublesome questions.

Like all our Concept Builders, this Concept Builder utilizes a variety of strategies to make each student's experience different. The ordering of questions is random. The Question number assigned to each question is scrambled. For instance, two side-by-side students will not have the same question for question number three. And questions are organized into "groups" with questions within the same group being very similar (for instance, they have the same type of representations) but not identical.

The Concept Builder also keeps track of student progress. It requires that students demonstrate a mastery of questions in each Question Group. If they miss a question from one group, then they will have to answer two consecutive questions correctly in order to demonstrate mastery. Progress is displayed in the progress report on the right side of the Concept Builder. A star indicates a demonstration of mastery. A question with a red background indicates that the student has missed the question. And a question with a yellow background means that the student must get one more question from that Question Group correctly answered in order to obtain a star. When an activity is completed, the student will be awarded a Trophy. This Trophy is displayed on the Main Menu screen. These strategies make the Concept Builder an ideal addition to the 1:1 classroom and other settings in which computers are readily available. 


In order to complete a difficulty level, a student must correctly analyze each question of that difficulty level. If a student's analysis is incorrect, then the student will have to correctly analyze the same or very similar question twice in order to successfully complete the activity. This approach provides the student extra practice on questions for which they exhibited difficulty. As a student progresses through an activity, a system of stars and other indicators are used to indicate progress on the activity. A star is an indicator of correctly analyzing the question. Once a star is earned, that question is removed from the que of questions to be analyzed. Each situation is color-coded with either a yellow or a red box. A red box indicates that the student has incorrectly analyzed the question and will have to correctly analyze it twice before earning a star. A yellow box is an indicator that the question must be correctly analyzed one time in order to earn a star. Once every question of a difficulty level has been analyzed, the student earns a Trophy which is displayed on the Main Menu. This system of stars and trophies allows a teacher to easily check-off student progress or offer credit for completing assigned difficulty levels.

The most valuable (and most overlooked) aspect of this Concept Builder is the Help Me! feature. Each question group is accompanied by a Help page that discusses the specifics of the question. This Help feature transforms the activity from a question-answering activity into a concept-building activity. The student who takes the time to use the Help pages can be transformed from a guesser to a learner and from an unsure student to a confident student. The "meat and potatoes" of the Help pages are in the sections titled "How to Think About This Situation:" Students need to be encouraged by teachers to use the Help Me! button and to read this section of the page. A student that takes time to reflect upon how they are answering the question and how an expert would think about the situation can transform their naivete into expertise.