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.

Application of Hess's Law can be a troublesome part of a Chemistry class for many students. This Concept Builder should help. It provides nine opportunities (or more, when there are misses) to practice. The process involves adding two or more given equations in order to generate the target equation. The process is simplified through the use of our online interface. Students can quicly click on a button and have the equation reversed. Or they can click on a mulitplier and have all the coefficients instantly changed. They can then begin to focus on Hess's Law and the effect of these manipulations on the ∆H of the given equations. Once they have effectively produced the target equation, they will have to calculate the ∆H of it.

The questions are shown on a separate page (viewable by logged-in teachers only). Teachers are encouraged to view the questions in order to judge which levels are most appropriate for their classes and what level of preparation and practice would be required. We recommend doing the levels in order and we emphasize that the third level (Wizard) is most essential. There is no redundancy in the levels. The Apprentice and the Master level utilize equations with fictional substances - A, B, C, ... F. The questions provide an excellent opportunity to manipulate and add the given equations to yield the target equation. The Wizard level uses real substances and includes actual reactions.

Our Concept Builders typically utilize a variety of strategies to make each student's experience different. For instance, questions are grouped into Question Groups. The Question Groups randomly numbered such that one student's Group #1 is another student's Group #3. Questions from within the group are selected at random such that two side-by-side students working on the same Question Group are more likely to have a different question than the same question. And the order in which Question Groups are presented to students is scrambled and unlikely to be the same order for two side-by-side students.
 

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.