13: Rate and Order of Chemical Reactions

kinetics

motion or movement as a function of time

rate of a chemical change

reactions rate depends on what conditions?

- reactant concentration
- temperature
- moisture
- radiation (light)

what conditions do reaction rates in liquid preparations depend on?

- presence of solvents or additives
- pH of the liquid preparation
- concentration of buffer components
- catalytic agents

the order of a process

refers to the way in which the concentration of the drug or reactant in a process or chemical reaction influences the rate

zero-order reaction equation

dC/dt= -k

first- order reaction equation

dC/dt = -k [C]

zero-order is ______________ of concentration

independent

first-order is _____________ of concentration

dependent

zero-order kinetics

the reaction rate is independent of the concentration the reacting substance, it depends on the zero power of the reactant

half-life

the period of time required for the concentration, amount or potency of a reactant ( or drug) to decrease by one-half

zero-order half-life equation

t1/2= Co/2k

shelf-life is represented by what?

t10%

zero-order shelf-life equation

t10%= 0.1C/k

shelf-life

the time required for 10% of a drug to degrade (t1/10, t0.1, t10% or t10)

zero-order kinetics follows

a constant degradation

first-order kinetics follows

drugs does not degrade mathematically

an increase in the storage temperature causes

an increase in degradation rate

Arrhenius equation

long k2/k1 = Ea (T2-T1)/ 2.303 x R x T1 x T2