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Title: Exothermic and Endothermic Reactions
Principle(s) Investigated: Chemical Reactions, Heat of Reactions (D H), Energy Changes
Standards : PS1B Chemical Reactions : Undertake a design project to construct, test, and modify a device that either releases or absorbs thermal energy by chemical processes
PS3D Energy and Chemical Processes in Everyday Life : Plan an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and the change in the average kinetic energy of the particles as measured by the temperature of the sample.
Materials: Vinegar, Baking soda, Calcium chloride, Water, Thermometer,4 small clear plastic cups,
1 cup measuring cup,Measuring spoons (1 tablespoon, ½ teaspoon)
Procedure:In the first part,you will study the reaction between acetic acid (vinegar) and sodium bicarbonate (baking soda).
An equation for the reaction is: HC2H3O2 + NaHCO3 NaC2H3O2 + H2O + CO2 a
Step 1: Add approximately 50 ml of acetic acid to a large test tube.
Step 2: Record the temperature of the acetic acid.
Step 3: Add a small scoop of sodium bicarbonate to the acetic acid.
Step 4: Gently stir (with the thermometer) until all sodium bicarbonate has been dissolved. Observe the temperature, record any temperature change and other observations.
Step 5: Discard the solution into the correct area and clean your equipment.
In the next part, you will study the reaction between calcium chloride and water.
An equation for the reaction is: CaCl2 + H2O CaCl2 + H2 + O2
Step 1: Add approximately 50 ml of water to a large test tube.
Step 2: Record the temperature of the water
Step 3: Add 5 grams of calcium chloride to the water.
Step 4: Gently stir (with the thermometer) until all calcium chloride has been dissolved. Observe the temperature, record any temperature change and other observations.
Step 5: Discard the solution into the correct area and clean your equipment.
Use spreadsheet provided here:
Student prior knowledge: Students should understand the concepts of energy and energy transfer. They should have a basic understanding of heat energy and will have covered the definitions of endothermic and exothermic. In addition to energy the students should also be familiar with solutions, compounds, and mixtures as well as chemical equations. Balancing equations should have been covered as well as concepts such as activation energy and enthalpy.
Explanation: Chemical reactions that release energy are called exothermic. In exothermic reactions, more energy is released when the bonds are formed in the products than is used to break the bonds in the reactants. Chemical reactions that absorb (or use) energy are called endothermic. In endothermic reactions, more energy is absorbed when the bonds in the reactants are broken than is released when new bonds are formed in the products. If a chemical reaction absorbs as much energy as it releases, it is called isothermic—there is no net energy change.
Since we cant actually see the bonds being broken we look at the difference, by comparing the starting temperature and subtracting the ending temperature. The result is a DH that is either positive or negative.
If ΔH is negative (−) then the chemical reaction is exothermic, because more energy is released when the products are formed than energy is used to break up the reactants. If ΔH is positive (+) then the chemical reaction is endothermic, because less energy is released when the products are formed than the energy is used to break up the reactants.
Questions & Answers:
1. In the Baking Soda and vinegar reaction, what other changes were noticed?
A: Since this was a neutralizing reaction we noticed the reaction bubbled up and foamed over when the baking soda was added to the vinegar. This gas must have been carbon dioxide released during the reaction
2. What might happen if we used a baking soda solution instead of plain water for the calcium chloride reaction?
A:We likely would have seen a similar reaction between the baking soda solution and vinegar. The difference would likely be that this is still an exothermic reaction, so temperature should rise
3. What is a solid exothermic reaction that we could experiment with, or already have?
A: The burning of magnesium metal and watching it convert to magnesium oxide
Applications to Everyday Life:
1.The burning of fuels and the creation of different kinds of fuels for industry
2.Chemical ice packs that are use for sports injuries. They are an endothermic reaction that produces the effect of cold without the liquid mess of ice
3.The use of calcium chloride on sidewalks and roads instead of rock salt to keep them ice-free
Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.
Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.
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