Review/IntroductionToday we will be working with some acids and a base we learned about before: Vinegar and Citric acid (which is found in fruits like lemons and oranges), and baking soda, which we use for lots of things such as cooking, removing bad smells, and cleaning.
Remember that when you put an acid together with a base, they create something called a reaction. A reaction between chemicals happens when two chemicals are mixed together and the molecules of one chemical break their bonds and form new ones with the molecules of the other chemical to form a new chemical. A reaction does not always have to include adding chemicals together, though.
Endothermic ReactionsEndothermic Reactions are reactions that need energy in the form of heat, to happen or proceed. You put heat INTO it.
Examples of some endothermic reactions:
-Ice melting is an example of an endothermic process** (not a reaction) (corrected this oversight as per the 11/13/12 comment below)- it needs heat energy to happen.
-Trees and plants use an endothermic reaction called photosynthesis to make food. They need the heat and light from the sun to do this.
- The intake of energy may be observed as a decrease in temperature as the reaction proceeds. Once the reaction is complete, the temperature of the mixture will return to room temperature.
Activity: Feel an Endothermic Reaction
- Mix Citric Acid solution in a plastic cup with baking soda solution
- Allow kids to place two fingers into the cup to feel the reaction. They should feel it bubble more vigorously and their fingers should feel cold after a bit.
- Ask them to describe what they feel/felt. See if they can explain where the heat in their fingers is going.
- Explain: When you put your fingers in the solution, it will bubble and speed up because you're giving the acid and the base mixture the heat energy it needs to get going and keep going.
- Also, it's taking the heat from your fingers so your fingers will feel cold in the solution and when you remove them.
Exothermic ReactionsExothermic Reactions give off heat as they happen. They are the opposite of an endothermic reaction.
-When salt is made from Sodium and Chlorine (remember our periodic table), this is a reaction that gives off heat, or an exothermic reaction
-When you light a match, this is an exothermic reaction
Activity: Feel an Exothermic Reaction
Make Hot Ice ahead of time according to the recipe and method at the link below. Touch it to demonstrate how it crystallizes. Let the kids feel it giving off heat.
**I tried making this and got nothing TWICE and this did not work for me either time. I have no idea what I did wrong but I'd be interested to know if you're able get it to work.**
Activity: See a chemical reaction between Mentos & Diet Soda (Teacher-Demonstrated, Outdoors)- An exothermic reaction
What we did: We used a bottle of Diet Coke (because there's no sugar, it easily washes away without becoming sticky) and added the Mentos to it using a rolled. I used I strongly recommend if you want real fireworks that you add at least half to three quarters of the pack. I stuck with a website's recommendation of "4 Mentos" and this was a disappointment for me, although the kids thought it was great either way. Needless to say, I will be repeating the experiment with a bigger "bang" next time. Can't wait!
Show video either before or after demonstration: http://www.youtube.com/watch?v=LjbJELjLgZg&feature=related
Activity: Coloring Page: http://www.kookerkids.com/Coloring/school_days/chemistry.htm
All images taken from http://www.publicdomainpictures.net/