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Investigating Heat – Investigation 3 CAP


Investigating Heat: Investigation 3 – CAP


In this short CAP, we wish to talk about both the Law of Conservation of Energy and the Law of Conservation of Matter. At this point, the thing that we would like you to appreciate is that neither energy nor matter can be destroyed or created. When energy or matter seems to disappear, it is only that they have changed form, but the exact same amount of energy and matter will always exist regardless of what form transitions have taken place.


In this first slide, we simply state the two laws of conservation and give an example for each.


This slide deals with the Law of Conservation of Energy that states that energy cannot be created or destroyed but can change forms. In this case, electrical energy supplied by the batteries is converted into light energy by the two light bulbs. In addition to light, incandescent bulbs also produce a large amount of heat from the electrical current. So, in this example, electrical energy is converted into both light and heat energy. However, no energy is created or destroyed. If we were to determine how much light and heat were generated by the lightbulb, we would find that it was exactly the amount of electrical energy that was supplied. Thus the electrical energy was changed but there was no net gain or loss of energy.


This is the first of three slides devoted to the Law of Conservation of Matter. This law states that matter cannot be created or destroyed, but can change form. The example we are using is that of an antacid tablet composed of magnesium hydroxide Mg(OH)2. Stomach acid, hydrochloric acid or HCl, is secreted by cells lining the inside of the stomach to aid in the digestion of food. Sometimes too much acid causes stomach problems. While modern drugs target the release of HCl, an antacid is used to neutralize the acid in the stomach once it is already present.


In the experiment shown in this slide an antacid tablet, composed of the chemical magnesium hydroxide Mg(OH)2, is added to a certain volume of hydrochloric acid (HCl). Hydrochloric acid is an acid secreted by the stomach lining to help break down and digest food. As seen in the slide, the total mass of the acid and antacid tablet is 31.5 grams. After the reaction is complete, the antacid and hydrochloric acid have been completely transformed into two new products magnesium chloride (MgCl2) and water (H2O). IMPORTANTLY, the mass of the two products is EXACTLY the same as the two starting materials, 31.5g. Thus, although the composition of the reaction changed completely, there was no increase or decrease in mass. Therefore, matter was neither created nor destroyed as a result of the reaction.


The last two slides are too advanced for elementary students at this point but are included simply to set the stage for middle school when chemical reactions are studied in greater detail.


This final slide is included simply to introduce you to the name Einstein and his most famous equation. Einstein’s brilliant idea is that matter and energy are not only related to each other (E=mc2) but can actually be converted into each other. You will see this equation again in middle school and beyond.

Knowing that matter and energy are interconvertible helps explain how the laws of the conservation of matter and the conservation of energy are also related and sound so similar when stated. Neither matter nor energy can be created or destroyed.