# why does a change in temperature indicate a chemical reaction

Aside from bubbling, what else happens during a reaction between baking soda and vinegar? In each of the previous activities, students observed bubbling and learned that this was evidence that a chemical change occurred. In this activity, students will observe another aspect of the reaction between baking soda and vinegar. Along with bubbling, students will see that the temperature decreases. A change in temperature is another clue that a chemical reaction has occurred. A reaction that results in a decrease in temperature is called an endothermic reaction. Be sure you and the students wear properly fitting goggles. The bulb of the thermometer needs to be completely submerged in the vinegar in order to get an accurate reading. Due to the small amount of vinegar suggested in the procedure, you may need to have students tilt their cups of vinegar so that the bulb of the thermometer is completely submerged. If your thermometers have a plastic backing, you may be able to lower the bulb by clipping the plastic backing so that it is even with the bottom of the bulb. Label 2 small cups vinegar and baking soda. Place about 1 tablespoon of vinegar and about 1 teaspoon of baking soda in their labeled cups.

Note: If you plan to do immediately after this activity, increase the amounts to 4 tablespoons ( cup) vinegar and 1 tablespoon baking soda. These source cups can then be used for both activities. Download the, and distribute one per student when specified in the activity. An assessment rubric for evaluating student progress during this activity is via download on this page. For this formative assessment, check a box beside each aspect of the activity to indicate the level of student progress. Evaluate overall progress for the activity by circling either Good, Satisfactory, or Needs Improvement.
Let's start with the idea of a chemical reaction. Reactions occur when two or more molecules interact and the molecules change. between atoms are broken and created to form new. That's it. What molecules are they? How do they interact? What happens? The possibilities are infinite. When you are trying to understand chemical reactions, imagine that you are working with the. Imagine the building blocks are right in front of you on the table. Sometimes we use our chemistry toys to help us visualize the movement of the atoms.

We plug and unplug the little connectors that represent chemical bonds. There are a few key points you should know about chemical reactions: 1. A chemical change must occur. You start with one molecule and turn it into another. Chemical bonds are made or broken in order to create a new molecule. One example of a chemical reaction is the rusting of a steel garbage can. That rusting happens because the iron (Fe) in the metal combines with oxygen (O ) in the atmosphere. Chemical bonds are created and destroyed to finally make iron oxide (Fe ). When a refrigerator or air conditioner cools the air, there is no reaction in the air molecules. The change in temperature is a physical change. When you melt an ice cube, it is a physical change. When you put bleach in the washing machine to clean your clothes, a chemical change breaks up the molecules in your stains. 2. A reaction could include atoms, compounds, or molecules of a single element. You need to remember that a chemical reaction can happen with anything, just as long as a chemical change occurs.

If you put pure hydrogen gas (H ) and pure oxygen gas in a room, they might be involved in a reaction to form water (H O). However, it will be in very very small amounts. If you were to add a spark, those gases would be involved in a violent chemical reaction that would result in a huge explosion (exothermic). Another chemical reaction might include silver ions (Ag ). If you mix a solution with silver ions with a solution that has chloride (Cl ) ions, silver chloride (AgCl) precipitate will form and drop out of solution. 3. Single reactions often happen as part of a larger series of reactions. When a plant makes sugars, there might be as many as a dozen chemical reactions to get through the Calvin cycle and eventually create (synthesize) ) molecules. The rusting example we used earlier only showed you the original reactants and final products of the chemical reaction. There were several intermediate reactions where chemical bonds were created and destroyed. The silver chloride example only focused on the ions. In reality, the two solutions were created when two salts dissociated (split into ions) in water.

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