exothermic reaction and endothermic reaction
Introducing experiments on chemical reactions and temperature changes. I will introduce two heat generation and two endothermic reactions.
Experiment 1: Delicious endothermic reaction
To be precise, there is an exothermic reaction on the way, so there is a problem, but it is delicious, so I will put it on.
you need : baking soda, citric acid, granulated sugar, water
Mix baking soda and citric acid in a 2: 1 ratio. Add as little water as possible to it and cut it out. The bath salt is complete.
When you put water in a beaker and add a bath salt, citric acid reacts with baking soda to generate carbon dioxide. At this time, the temperature of the water drops below the ambient temperature.
C5H8O7 + 300873 → Na3C6H5O7 + 3H2CO3, but heat is generated at this time. Immediately after that, the following reaction occurs.
H2CO3 → H2O ＋ CO2 At this time, it absorbs the ambient temperature. In the photo on the left, the temperature has dropped by about 10 ° C.
Well, here is the actual production. It is the foaming of carbon dioxide that makes you feel refreshed when the acid (citric acid) and alkali (baking soda: sodium hydrogen carbonate) undergo a neutralization reaction. If you add sweetness to it, it becomes a ramune confectionery.
Add 1/4 teaspoon of baking soda and 1/4 teaspoon of citric acid, and add 1 tablespoon of granulated sugar. Stir with a minimum of water and cut out. The ramune confectionery is completed. If you eat this and experiment with the endothermic reaction of ammonium chloride and sodium hydroxide, which are treated in textbooks, students will never forget the endothermic reaction.
Experiment 2: Make quicklime for exothermic reaction and check the exothermic reaction.
you need : Egg shell or chalk (some of which are not calcium carbonate these days), muffles, heating appliances
Calcium carbonate (use egg shells or chalk. Limestone takes a lot of effort to heat) is crushed and heated with a muffle. After heating for about 15 minutes, it becomes quicklime CaO. When there is no muffle, the wind is blown from below to heat it up. I had a hard time in Ethiopia. If you have quicklime, you won't have any trouble.
CaCO3 → CaO + CO2 This is a reaction from calcium carbonate to quicklime when heated. It requires a tremendous amount of heat.
CaO ＋ H2O → Ca (OH) 2 This is a reaction from quicklime to slaked lime. At this time, it generates heat.
Experiment 3: Let's make a body warmer
you need : Iron powder 10g, charcoal (activated carbon is better) 1g, concentrated saline solution 2ml, kitchen paper, plastic bag
Mix iron powder and activated carbon well to add salt solution. Wrap it in kitchen paper and put it in a plastic bag. It can be easily rubbed by hand and the reaction can occur easily. The temperature begins to rise. It depends on the amount, but if it goes well, it will generate heat to about 70-80 ° C.
The experiment is simple, but the substance produced by the reaction is ferric hydroxide, not iron oxide. Therefore, I think it is better not to touch the reaction formula in junior high school. Salt acts as a catalyst.
4Fe + 3O2 + 6H2O → 4Fe (OH) 3
Experiment 4: Melt urea and investigate temperature changes
you need : urea 20g, water 20ml, thermometer, beaker
Urea undergoes an endothermic reaction when dissolved in water, causing the temperature to drop significantly. Urea and water are used in common cooling packs, and the heat of fusion when urea dissolves in water is used to lower the ambient temperature. Besides urea, ammonium nitrate is used.
Prepare 20 g of urea and 20 ml of water. Put urea in the beaker, then add water. The temperature goes down steadily. If you want to lower it in a short time, stir it with a glass rod to dissolve the urea more and more. The temperature drops by nearly 20 ° C. Urea absorbs about 15 KJ / mol of heat as it dissolves. It is sold as a fertilizer for gardening at home improvement stores, so it is easy to dispose of.
Performing endothermic reactions 15kJ when urea 1 mole to about 60g is dissolved. A total of 40 g of urea and water can be lowered by about 29 ° C. In reality, it does not completely melt, and the temperature drops by about 20 ° C. In addition, there are many endothermic reactions such as salt and potassium nitrate when they dissolve.