Transcript Document
2.4 Chemical Reactions Sponge: Set up Cornell Notes on pg. 17 2.4 Chemical Reactions The topic or heading will always be at the top of the Powerpoint. Include the # Ex: 2.3 Carbon Based Molecules Essential Question: Describe how bonds break and form during chemical reactions Don’t forget to add it to your T.O.Contents! Describe how bonds break and reform during chemical reactions Key Concept: 2.4 Chemical Reactions On pg. 16 When you hear the term chemical reaction, what comes to mind? Can you give an example of a chemical reaction? 2.4 Chemical Reactions ANSWER Maybe you think of liquids bubbling in beakers. You probably do not think of the air in your breath, but most of the carbon dioxide and water vapor that you breathe out are made by chemical reactions in your cells 2.4 Chemical Reactions KEY CONCEPT Life depends on chemical reactions. 2.4 Chemical Reactions Bonds break and form during chemical reactions. • Chemical reactions change substances into different ones by breaking and forming chemical bonds Ex: iron + oxygen= rust 2.4 Chemical Reactions On the top of Page 16 With your table: List as many different chemical reactions that you can come up with. 2.4 Chemical Reactions 2.4 Chemical Reactions – Reactants are the substances changed during a chemical reaction. – Products are the substances made by a chemical reaction. 2.4 Chemical Reactions On pg. 16: Name the reactants (2) and products (3) in the Gummi Bear chemical reaction. Reactants: • Sucrose- Gummi Bear • Molten Potassium Chlorate Products: • Carbon Dioxide • Water • Potassium Chloride 2.4 Chemical Reactions Name the reactants and products in the “Elephant’s Toothpaste” Video Name the reactants and products in the “Mentos and Diet Coke” Video Reactants • Hydrogen Peroxide • Liquid Soap • Potassium Iodide Products • O2 Foam Reactants • Mentos • Diet Coke Products • CO2 Foam 2.4 Chemical Reactions On pg 16: What is the difference between reactants and products? Give an example of each. 2.4 Chemical Reactions – Reactants are the substances changed during a chemical reaction. Ex: H2O2 + liquid soap + sodium iodide Answer – Products are the substances made by a chemical reaction. Ex: Oxidized Soap Foam + heat 2.4 Chemical Reactions • Bond energy is the amount of energy that breaks a bond between two atoms . – Energy is added to break bonds. – Energy is released when bonds form. • A reaction is at equilibrium when reactants and products form at the same rate. CO2 + H2O H2CO3 2.4 Chemical Reactions Chemical reactions release or absorb energy. • Activation energy is the amount of energy that needs to be absorbed to start a chemical reaction. *like the energy you would need to push a rock up a hill 2.4 Chemical Reactions • All chemical reactions involve changes in energy • Energy is both absorbed and released during chemical reactions • Whether a reaction releases or absorbs energy depends on bond energy 2.4 Chemical Reactions • Exothermic reactions release more energy than they absorbs –releases energy into its surroundings – Products have lower bond energy than the reactants. – Excess energy is released by the reaction often as heat or light or electricity Reactants------- products + energy 2.4 Chemical Reactions • Endothermic reactions absorb more energy than they release- absorbs energy from its surroundings in the form of heat – Products have a higher bond energy than the reactants – Lowers surrounding temperature Ex: Photosynthesis- carbon dioxide + water +sunlight (heat)= sugars+oxygen 2.4 Chemical Reactions With your group: Please use the internet to look up at least one of each • Exothermic reactions –Reactants and products • Endothermic reactions –Reactants and products 2.4 Chemical Reactions Exothermic reactions • Fuel + heat = explosion • Phosphorus +heat = fire • Catalyzed rusting of iron + calcium chloride= Hot Pack Endothermic reactions • Ammonium nitrate + water= cold pack • Heat + water= evaporation