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

2. 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

3. 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

4. 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

5. 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

6. 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!