Chemical Reactions Date: 12/7/2016 Mrs. Rebecca Collins

Energy in Chemical Reactions Endothermic Reactions “Taking in heat” Takes more energy to break bonds in reactants than is released when new bonds form Additional energy is required to keep reactions going General Equation: Reactants + Energy Products Heat is absorbed from surroundings and temperature drops

Energy in Chemical Reactions Exothermic Reactions “Turning out heat” Takes less energy to break bonds in reactants than is released when new bonds form Energy (heat) is released and temperature increases Combustion reactions are exothermic

Law of Conservation of Energy Energy cannot be created or destroyed - it only changes form. Endothermic or Exothermic - no overall change in energy Activation Energy Energy to get a reaction started Reactions can’t take place unless molecules are moving - takes energy to move them

Factors Affecting Rates of Reaction Temperature of Reactions When temperature of reactants is higher - reaction is faster Higher temps, particles have more energy. Move faster Concentration of Reactions Concentration is number of particles of a substance in a given volume When concentration of reactants is higher - reaction is faster Particles closer and more likely to run into each other

Factors Affecting Rates of Reaction Surface Area of Reactants Solid substance in chemical reaction - only surface of solid is exposed to other reactants More surface area - more exposure to reactants - faster reaction Presence of Catalyst Catalyst - substance used to speed up a chemical reaction - is not changed or used up in the reaction NOT reactants - but help reactants come together Decreases activation energy needed to start a chemical reaction Living things depend on catalysts to speed up reactions Enzymes - catalysts in cells Reactions take places in seconds - without enzymes might take billions of years!