2Chemical Bonds and Energy Chemical energy is the energy stored in the chemical bonds of a substanceChemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products
3Chemical Bonds and Energy Breaking BondsBreaking bonds requires energyThere has to be enough energy to break bonds of reacting molecules to get the reaction startedForming BondsThe formation of chemical bonds releases energyHeat and light are examples of what happens when new chemical bonds are formed
4Exothermic and Endothermic Reactions During a chemical reaction, energy is either release or absorbedExothermic ReactionsA chemical reaction that releases energy to its surroundingsThe energy released as the products form is greater than the energy required to break the bonds in the reactantsCombustion is an example of an extremely exothermic reaction
5Exothermic and Endothermic Reactions A chemical reaction that absorbs energy from its surroundingsMore energy is required to break the bonds in the reactants than is released by the formation of the productsEnergy of products is greater than the energy of the reactants
9Reactions Over TimeA reaction rate is the rate at which reactants change into products over time.Reaction rates tell you how fast a reaction is going.Some reactions happen almost instantaneously, while other happen gradually
10Factors Affecting Reaction Rates The reaction rate depends on how often the particles collide. If the collisions occur more frequently, then the reaction rate increases.Factors that affect reaction rates include temperature, surface area, concentration, stirring and catalysts
11Factors Affecting Reaction Rates TemperatureIncrease in temperature will generally increase the reaction rate.Increasing the temperature of a substance causes its particles to move faster, on average. Particles that move faster are both more likely to collide and more likely to react.
12Factors Affecting Reaction Rates Surface AreaThe smaller the particle size of a given mass, the larger is its surface are.An increase in surface area increases the exposure of reactants to one another.The greater the exposure, the more collisions
13Factors Affecting Reaction Rates StirringStirring the reactants will generally increase the reaction rateConcentrationConcentration refers to the number of particles in a given volume. The more reacting particles that are present in a given volume, the more opportunities there are for collisionsFor gas, concentration changes with pressure. The greater the pressure of a gaseous reactant, the greater is its concentration, and the faster the reaction rate.
14Factors Affecting Reaction Rates Catalystsa substance that affects the reaction rate without being used up in the reaction.Since the catalyst is neither a reactant nor a product, it is written over the arrow
16Types of EquilibriaEquilibrium is a state in which the forward and reverse paths of a change take place at the same ratePhysical EquilibriumWhen a physical change does not go to completion, a physical equilibrium is established between the forward and reverse changes
17Types of Equilibria Chemical Equilibrium When a chemical reaction does not go to completion, a chemical equilibrium is established between the forward and reverse reactionsA reversible reaction is a reaction in which the conversion of reactants into products and the conversion of products into reactant can happen simultaneously
18Factors Affecting Chemical Equilibrium When a change is introduced to a system in equilibrium, the equilibrium shifts in the direction that relieves the change- aka Le Chatelier’s principleTemperatureHeat written as a product, then forward reaction is exothermic; in the reverse reaction, heat is a reactantWhen heat is added to a system, the equilibrium will shift in the direction that removes heat from the system
19Factors Affecting Chemical Equilibrium PressureIf pressure is increased, the equilibrium would shift in the direction that decreases the pressure of the systemTo decrease pressure, the system would favor the reaction that produces fewer gas moleculesConcentrationChange in concentration of the reactants or products also affects equilibrium