Endothermic and exothermic reaction.pptx

ppt

1. Exothermic and Endothermic Reactions

2. Thermodynamics is the branch of physics that deals with the transfer of energy in the form of heat. There are two types of energy: potential energy and kinetic energy. In order for a chemical reaction to take place, the reactants must come into contact with each other and form molecules called intermediates. These intermediates then react to form the products of the reaction. The energy that is required for this process to occur is called the activation energy. In an endothermic reaction, the activation energy is greater than the amount of energy that is released by the reaction. This means that the reaction must absorb heat from its surroundings in order to take place. The heat that is absorbed is used to break the chemical bonds between the reactants and form the intermediates. Once the intermediates are formed, they react to form the products of the reaction. The heat that is released by this process is used to re-form the original chemical bonds. This means that the overall reaction is exothermic, meaning that it releases energy in

3. Energy and Chemical Reactions Chemical Energy – Energy stored in the chemical bonds of a substance. Chemical reactions always involve energy changes. Making bonds and breaking bonds involve energy changes

4. Activation Energy The energy required to break the bonds in the reactants for a chemical reaction to occur.

5. Endothermic and Exothermic reactions Step 1: Energy must be SUPPLIED to break chemical bonds of reactants: Step 2: Energy is RELEASED when new chemical bonds are made in the products: A reaction is EXOTHERMIC if more energy is RELEASED than SUPPLIED . If more energy is SUPPLIED than is RELEASED then the reaction is ENDOTHERMIC © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

6. Energy of Chemical Reactions Based on the type of energy (heat) change involved, chemical reactions are classified as either exothermic or endothermic . Exothermic : energy is released Exo- = “exit” Burning of gasoline Endothermic : energy is absorbed Endo- = “into” Cooking of pancakes

7. Endothermic Diagram Energy absorbed in reaction Activation Energy Energy used in bond breaking Endothermic – more energy is taken in to break the bonds in the reactants than released by the bonds being formed in the products. Therefore, energy is absorbed. Energy released in bond making

8. reaction Endothermic Heat (energy) taken in Temperature of the substance drops Products feel COLD

9. Endothermic Reactions You may see an endothermic reaction written like this… REACTANTS + ENERGY PRODUCTS OR REACTANTS + HEAT PRODUCTS

10. Exothermic Diagram Energy released in bond making Activation Energy Energy used in bond breaking Exothermic – More energy is released when the products where formed than energy was used to break bonds in the reactants. Therefore, a net release of energy.

11. reaction Exothermic Heat (energy) given off Temperature of the substance rises Products feel HOT

12. Exothermic Reactions You may see an exothermic reaction written like this… REACTANTS PRODUCTS + ENERGY OR REACTANTS PRODUCTS + HEAT

13. ENDOTHERMIC OR EXOTHERMIC? 6CO 2 + 6H 2 O + Energy C 6 H 12 O 6 + 6O 2 CH 4 + 2O 2 CO 2 + 2H 2 O + Energy ENDOTHERMIC! EXOTHERMIC!

14. Examples Exothermic Nuclear Fission Yeast & Hydrogen Peroxide Neutralisation of Acid and Alkalis Endothermic Photosynthesis Acetid Acid & Sodium Bicarbonate © Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910

15. https://www.youtube.com/watch?v=4FUZZuy7QmM

16. Exothermic reactions are reactions or processes that release energy, usually in the form of heat or light. The total energy of the products is less than that of the reactants. Thus, the change in enthalpy is negative and heat is released to the surroundings. Respiration is considered as an exothermic reaction because, in this process, oxidation of glucose takes place which produces a large amount of heat energy that are needed for survival. This is shown in following chemical equation: C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + Energy

17. Reaction of vinegar (acetic acid) and baking soda (sodium bicarbonate)