Experiments and explanations
Simonka, Nika, Evka
The chemical reactions in which heat is released into the environment, are called exothermic reactions. Products of exothermic reactions have less energy than the reactants, and therefore the stable chemical bonds are stronger. Into three beakers we poured 50 ml of water. With a thermometer we measured water temperature, which was 21 degrees. Into the first beaker we added two grams of NaOH in water and mixed together. The temperature of the solution rose to 26.5 degree. This is provement of exothermic process, since exothermic reactions are reactions in which heat is released.
Into the second beaker, we've added 2 g of sodium thiosulphate. The temperature after the addition of sodium thiosulfate dropped to 20.5 degree. The chemical reaction in which heat is taken from the environment, is called endothermic reaction. Endothermic reaction products have a higher energy than the reactants and the chemical bonds are weaker. Into the third beaker, we've added 2 g Na2CO3. Temperature after the addition of carbonate increased from the original 21 degrees to 22.5 degree. There was an exothermic reaction in which heat is released.
In the second task we dealed with temperature changes in the reaction of acid and the hydroxide. In the reactions that we have examined, the original temperatures have increased.
Self- heating coffee
The uniqueness of this drink is in the ability to instantly making hot drink without any heat source. The principle of heating works on base chemical reaction between calcium oxide and water which begins when you press the bottom of can. You can have hot coffee anywhere and any time you want only in three minutes. The temperature of coffee raise in 3 minutes to 40°C.
Samuel ,Miriam,Simona
Thermochemistry #1
Thermochemistry #2
Thermochemistry
Exothermic reactions
Exothermic reactions are defined as reactions in which the energy of reactants is bigger than the energy of products. Heat is released into the enviroment ,products are stabler than reactants.In our experiment we used 3 beakers ,in which we poured 50 ml of distillated water.
Into first beaker were added 2 grams of NaOH and into second 2 grams of Na2CO3 . Then we measured the temperature of this solutions. Intial temperature of both solutions was 20 °C. After few minutes we repeated this measurings and we discovered that the temparatures of both solution increased. Temperature of NaOH solution rised up to 26 °C and the temperature of Na2CO3 solution increased to 22.3 °C. According to this measurements is obvious that both reactions were exothermic ( heat was released from reactants).
Endothermic reactions
The definition of endothermic reactions describes ,that the energy of reactants is lower than energy of products and heat from an enviroment is consumed in order to take place of this reactions.
Into third beaker with water were added 2 grams of Na2S2O3. The intial temperature of this solution was 20 °C too. Then after 3 minutes we measured the temperature again. In this experiment the temperature of solution decreased to 19 °C. According to lower temperature is evident that this reaction was endothermic ( heat was consumed).
Self-heating coffee
Self-heating coffe is modern product, working through an exothermic chemical reaction between two chemicals. When this two substances combine, the reaction produces enough heat to raise the temperature of the can. This reaction is initiated by pressing on the bottom of the can and in only three minutes drink is heated up. The heating agent and responsible reaction vary from product to product.
Calcium oxide is used in the following reaction: CaO(s)+ H2O(l) → Ca(OH)2(s)
Copper sulphate and powdered zinc can also be used, but this process is less efficient:
CuSO4(s) + Zn(s) → ZnSO4(s) + Cu(s)
Anhydrous calcium chloride is often used as well. In this case, no chemical reaction occurs, instead the heat of solution is generated.