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.

Because enthalpy is a state quantity, the enthalpy change for reactants turning into products is the same for a 1-step process as it is for a multi-step process that beins with reactants and ends iwth the same products. The truth is often identified as Hess's Law and it forms the basis of this Concept Builder. In the second and third activity of the Concept Builder, students employ this idea in order to determine the ∆H for a reaction from knowledge of the ∆H_f values for all compounds present in the reaction. Students are guided through the process of decomposing reactant compounds and forming produt compounds. They must decide on the value of ∆H for each step. The results are displayed on an energy level diagram. Incorrect answers are responded to with feedback as to why they are incorrect. There is no "penalty" for missing the "individual step questions" other than the loss of time and a potentially bruised ego. Once the ∆H of the steps have been determined, students employ Hess's Law to determine the ∆H of the reaction. They have only one opportunity to get this calculation correct. If they miss the ∆H value question, then they will receive a similar question two more times until they demonstrate mastery.

The first activity of the Concept Builder is a warm up for Activities 2 and 3. In Activity 1, students are given a ∆H_f value for a compound and must identify any chemical equation and corresponding ∆H value that is consistent with the given ∆H_f value. The exercise will train them to give attention to +/- signs, to decomposition vs. formation processes, and to the coefficients in the equation and their effect upon ∆H values.

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 but not identical.

The Concept Builder also keeps track of student progress for those classes with Task Tracker accounts. 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 an activity, a student must correctly analyze each question of that Question Group. 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.