Topic 7

 Chemical Reactions Two or more substances undergo a reorganization of atoms to form other substances.  Reactants The substances that go into a chemical reaction  Products The substances that are produced from a chemical reaction Reactant + Reactant  Products

 When iodine is placed on a potato - a chemical reaction occurs and a blue-black colour is left. Colour change indicates a chemical reaction  When two solutions are put together – they may form a precipitate (solid) A precipitate and/or gas forming indicates a chemical reaction

 When charcoal is burned, a chemical reaction occurs. Heat and light production indicates a chemical reaction  When food spoils, its odour may change. Odour change can indicate a chemical reaction

1. Writing out word equations 2. Writing out chemical equations

 We know Baking soda and vinegar go through a chemical reaction.  Word Equation Baking soda + Vinegar  Sodium acetate + water + carbon dioxide  Chemical Equation

 Situation: Burning solid magnesium.  Word Equation  Chemical Equation  sFinTM&feature=related sFinTM&feature=related

 Energy is stored in chemical bonds  To break bonds – energy is required  To form bonds – energy is released

 Even though many reactions take and release energy, we look at whether it takes more or loses more.  Exothermic – Heat exits the chemical reaction  Endothermic – Heat enters the chemical reaction

 Burning gas in the car  Word equation Propane + oxygen  carbon dioxide + water  Chemical equation C 3 H 8(g) + O 2(g)  CO 2(g) + H 2 O (g) + energy  Even though you need to put a little energy in to start the chemical reaction, the heat produced is enough to keep the reaction going and more.

 Photosynthesis is a chemical reaction.  Is it exothermic or endothermic?

 Photosynthesis is a chemical reaction.  Is it exothermic or endothermic? Why? Energy ENters the reaction When you eat sugars and starches, you are eating molecules formed by endothermic reactions. Your cells break down these molecules in an exothermic process that supplies the body with energy. This exothermic process is called cellular respiration.

 Both hot and cold packs go through chemical reactions  Which goes through an endothermic reaction?  Which goes through an exothermic reaction?

 Both hot and cold packs go through chemical reactions  Which goes through an endothermic reaction? Cold Packs  Which goes through an exothermic reaction? Hot packs