Chemical Kinetics

Kinetics Rates of reactions How reactions happen Series of steps from reactant to product

Rate of Reactions Particles must collide for chemical change to occur Most reactions take several steps Have an intermediate product Example: A + B  intermediate product A + intermediate product  C Net Equation: 2A + B  C

Factors affecting rate 1. Nature of reactants (intramolecular forces) Ionic substances react faster than covalent bonds Ionic bonds are simpler to separate

2. Temperature Higher temperature = higher kinetic energy Molecules collide more frequently Rate increases

3. Concentration More molecules = more likely to collide Increases rate of reaction

4. Pressure Volume is decreased, pressure is increased Molecules closer together and collide easier Increases rate of reaction

5. Catalysts 6. Inhibitor Substance that speeds up the reaction rate Doesn’t change itself in the process Example: Enzymes 6. Inhibitor Opposite of a catalyst Slows the reaction rate

Reaction Mechanisms

Kinetics Rates of reactions How reactions happen Series of steps from reactant to product

Rate of Reactions Particles must collide for chemical change to occur Most reactions take several steps Have an intermediate product (something made but used in another step) Example: A + B  intermediate product A + intermediate product  C Net Equation: 2A + B  C

Net reaction is the sum of the intermediate steps If identical substances are on opposite sides, they cancel each other out If identical substances are on the same side, they are added together Some reactions have catalysts to speed them up Catalyst present at beginning and end of reaction but does not show up in the net reaction

Graphing Reaction Mechanisms When molecules react Intermediate products are called the activated complex Activation energy- minimum amount of energy needed to form intermediates

Potential Energy Diagrams X axis- time (progress of reaction) Y axis- potential energy ΔH – enthalpy (heat of the reaction= energy absorbed or released) ΔH = Energyproducts – Energy reactants

Endothermic reaction Products have more energy than reactants Energy is absorbed to make the product ΔH (enthalpy) is positive

Exothermic reaction Reactants have more energy than products Energy is released to make the product ΔH (enthalpy) is negative