Endothermic and Exothermic Reactions Endothermic • Endo= ? in heat • Therm = ? • What does endothermic mean? • A chemical reaction that needs energy added to it for the reaction to take place (energy is taken IN when it occurs). Exothermic • Exo = ? out heat • Therm = ? • What does exothermic mean? • A chemical reaction that gives off energy when the reaction takes place (energy is EXiting when it occurs). Properties of Endothermic Reactions • If energy goes IN for the reaction to occur, would energy be a reactant or a product? –Energy is a reactant • If energy is ABSORBED, would it feel hot or cold to the touch? –It would feel cold--it’s absorbing energy from the surroundings Properties of Exothermic Reactions • If energy EXITS when the reaction occurs, would energy be a reactant or a product? –Energy is a product • If energy is RELEASED, would it feel hot or cold to the touch? –It would feel hot--it releases energy to the surroundings Examples of Endothermic Reactions • Cold packs • Evaporation of water • Melting of ice Demonstration of Endothermic Reaction • NH4Cl(cr) + H2O(l) + energy --> + NH4 (aq) + Cl (aq) + H2O(l) • What are the reactants? • What are the products? • What are the states of matter? Examples of Exothermic Reactions • Hot Packs • Burning coal • Freezing ice Demonstration of Exothermic Reactions • 2 Al(cr)+ 3CuCl2 (aq) --> + energy 3Cu(cr)+ 2AlCl3 (aq) • • • • • What are the reactants? What are the products? Can you balance the equation? What are the states of matter? Heat pack Is it Endothermic or Exothermic? 1. When a lit match is placed in alcohol, the alcohol ignites producing light and heat. 2. Energy in the form of electricity can be added to water to break apart the water molecules into hydrogen gas and oxygen gas. 3. When ammonium chloride mixes with water, the solution formed feels cold. 4. A piece of wood placed in a furnace gives off heat and light before turning to ash.