Kinetics

Kinetics Collision Theory is the branch of chemistry that is concerned with the speed of a chemical reactions( reaction rates) and the way in which reactions occur (reaction mechanisms) Collision Theory • Collisions between particles can produce a reaction if both the spatial orientation and energy of the colliding particles are conducive to a reaction. • Reactants must collide in order for a reaction to take place • reactions involve breaking existing bonds and the formation of new bonds

Factors that Effect Reaction Rates Pressure Only on a gas has no effect on a solid or liquid increase pressure on a gas increases concentration-- increasing rate Nature of the reactants • bond type • ionic react more quickly than covalent- because they have few bonds to break and rearrange. 2Fe + O2 = 2FeO is slow Ag NO3 + NaCl is quick Surface area As the surface area increases the number of collisions increases, therefore… the rate of the reaction will increase Factors that Effect Reaction Rates Concentration As the concentration [ ] of the reactants increases -- the number of collisions increases and the rate of the reaction generally increases Temperature Increasing temperature increases the average kinetic energy of the particles -- increasing the number of effective collisions-- -- increasing the rate of a reaction Best way to speed up a Catalyst a catalyst lowers the activation energy therefore increasing the speed of the reaction

Q = mc∆T Calorimetry is the study of heat and heat transfer Calorimeter an instrument used to indirectly measure the amount of heat released or absorbed by a substance mass mass of the substance measured in grams most common water 1ml water = 1g of water specific heat amount of energy needed to raise 1g 1˚ C water 4.18J/g˚C 4.18 J/gK Change in temperature Final T- Initial T ˚C or K determine the sign of Q Joule unit of energy measures the amount of energy released or absorbed - Q = exothermic + Q = endothermic Types of energy: -chemical (bonds breaking/forming) -mechanical- movement, machine -electrical- transport of e-’s -thermal- heat transfer -nuclear- mass to energy

Conservation of Energy Heat Lost = Heat gained the amount of heat lost by one substance equals the amount heat gained by the other substance. Heat moves from Hot to cold Heat of Fusion Heat of Vaporization During a Phase Change remember no change in temp. amount of heat needed to change one gram of solid to one gram of liquid at its melting pt. amount of heat needed to change one gram liquid to one gram of gas at boiling pt. Heat of vaporization for water 2260J/g at 100˚C and 1 atm Heat of fusion for solid water is 334 J/g at 0˚C and 1 atm q = mHf q = mHv

Exothermic Endothermic Potential Energy Diagrams Activation Energy Increasing P.E. Time of rxn Act. complex React. Product Activation Energy the amount of energy needed to form an activated complex a reaction must achieve this point in order to occur 4 2 5 3 6 1 Catalyst a substance that alters the speed of a reaction without being permanently changed -lower the activation energy 1 = Potential Energy (PE) of the reactants 2 = PE of the activated complex Activated Complex the temporary intermediate product in a chemical reaction 3 = PE of the products 4 = Activation energy of the forward reaction (left to right for reading diagram) 5 = Activation energy of the reverse reaction (read right to left in diagram) 6 = Heat of reaction –ENTHALPY ∆ H = PE products - PE reactants

Low energy (exo) and Very messy (high entropy) Enthalpy (heat = H ) Amount of heat released or absorbed by a reaction + Q(H) = endo - Q(H) = exo Hf = heat of formation energy for one mole Entropy (disorder = S) “messy” measure of disorder When – + S = entropy increases - S = entropy decreases Dependent on 1. # of molecules 2. State of matter In nature--- Low energy (exo) and Very messy (high entropy) Spontaneous Reactions Once a reaction is started No more energy is required to Keep it going G is spontaneous Predicating spontaneousness G = spontaneous + G = not spontaneous