Chapter 14 - Chemical Kinetics

Chemical kinetics

The study of how fast chemical reactions occur

Factors affecting chemical kinetics

Concentration of reactants

Temperature

Presence of a catalyst

Surface area of a solid reactant or catalyst

Concentration effect on kinetics

More concentration, faster reactions

Temperature effect on kinetics

Higher temperature, molecules hit into each other harder

Catalyst

Substance that increases the rate of a reaction without being consumed in the overall reaction

Reaction rate

an increase or decrease in the molecular concentration odf product of the reaction per unit time

instantaneous rate

the tangent to the curve at any given time

rate law

an equation that relates the rate of a reaction to the concentrations of reactants and catalysts raised to various powers

\

in what does the speed of the reaction depends

the speed of the reaction only depends on the amount of reactants

rate constant

k, only changes with temperature

overall order

sum of all orders

the rate constant is a function of what

temperature only

rate constant unit when overall order is 1st

s-1

rate *constant* unit when overall order is 2

M-1 s-1

rate *constant* unit when overall order is 3

M-2 s-1

rate *constant* unit when overall order is 4

M-3 s-1

half life

the time it takes for the reaction concentration to decrease to one half of its initial value

collision theory

in order for a reaction to occur, reactant molecules must collide with an energy greater than some minimun value and with the proper orientation

energy of activation

the minimum energy of collision required for two molecules to react

reaction mechanism

the steps in the overall reaction

intermediate

compound created and consumed immediately

elementary reaction

a single molecular event resulting in a reaction, a step in the reaction mechanism

catalysis

the increase in the rate of a reaction as a result of the addition of a catalysth

homogeneous catalyst

same phase

heterogeneous catalyst

different phase

molecularity

the number of molecules on the reactant side of an elementary reactionr

rate determining step (slow step)

slowest step in the mechanism, fast steps after slow ones are insignificant

transition state theory

explains the reaction resulting from the collision of two molecules in terms of an activated complex

activated complex (transition state)

an unstable group of atoms that can break up to form two products

enzymes

biological catalysts

active site

where reactants attach to enzymes