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Home Concept Builders Thermochemistry Hess's Law Directions

Hess's Law - Directions

Using the Hess's Law Concept Builder is quite simple. There are three difficulty levels, each of which involves the same type of task - manipulating two or three given equations in order to produce the target equation. Once done, you will need to use the ∆H value for the given equations to calculate the ∆H of the target equation. Here is how you will do it:

The given equation and the target equation are labeled and displayed in bold red text. The grey text below the given equation is the manipulated version of the given equation. You can change this version using the two buttons to the left of the given equation. The small icon labeled R | P (for reactant and product) can be used to reverse the equation. One tap reverses it. The second tap changes it back to the original form. The current form of the equation is reversed if the icon displays as P | R. The x1 icon can be used to multiply through all the coefficients by the same factor. Tapping once on the icon pops up the Multiplier pad. There are five multiplying factors and a Cancel button. Tap one of the multiplying factors to multiply the coefficient in front of each substance by that factor. Your goal is to produce the target equation. The result of all your manipulations is shown at the bottom of the Concept Builder. Keep trying changes until you produce the target equation. Once you do, a green check will appear at the bottom and you will no longer be able to make changes.

At this point a Number Pad slides in and you will have to use it to enter the ∆H of the target equation. Use Hess's Law, the given ∆H values, and the manipulations you've made to calculate ∆H. Then use the number pad to enter the value. If applicable, be sure to enter a negative sign using the +/- button. If you are satisfied with your answers, tap on the Check Answer button. Your answer will be evaluated and your Progress Report will be updated.

Your goal is to earn "Stars" and to complete one or more levels. Stars are earned when you show success on a particular Question Group. If you miss a question then you will have to answer two other questions from that Question Group correctly before earning a star. Once you show success on all the Question Groups for a particular level, you will earn the trophy for that level.

Concept Builder Teacher Notes