Chem module 2

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Rate of a Chemical Reaction is

-is measured as a change in amounts of reactants or products divided by the change in time
-typical units are M/sec or M/min
-defined as the negative change of concentration of the reactant per unit time


Differential Rate Law: describes the relationship of

-the rate of the reaction and the concentration of the reactants


Reaction Order

-its magnitude determines how the rate depends on the concentration of the reactant
-it can be determined from the stiochiometry of the reaction
-it can be determined by the method of initial rates


Rate = k[IO ­ ][I­ ]^2[H+]^2

-this reaction rate is first order with respect to [IO} and fifth order overall


If the plot of [blank] vs time yields a straight line the reaction is in first order

the natural log of the concentration of the reactant ln[reactant]


Chemical reactions that proceed at a rate that is proportional to the square of the concentration of the reactant are

second order reaction


if the half life of a reaction depends on the initial concentration than the reaction order can not be

first order

t1/2 = 0.693/k

*does not depend on the initial concentration


The rates of chemical reactions are susceptible to temperature. The temperature dependence on the reaction rate is contained in which component of the rate law expression

rate constant


An Arrhenius plot is a plot of

natural log of the ln[rate] constant VS inverse of the temperature in kelvin


what can be calculated from the slop of the Arrhenius Plot

Activation Energy


the minimum amount of energy that reactant particles must posses in order for their collision to result in formation of products is called

Activation Energy


reaction intermediates

are formed in one step of the chemical reaction and consumed in another step


The Arrhenius equation below expresses the relationship between the rate constant, k, of a reaction and the activation energy, Ea, and the temperature, T.

k = Ae^(—Ea/RT)

according to eq.

reactions at constant temperature, and lower Activation energy proceed more rapidly


A catalyst

lowers the activation energy of a forward and reverse reaction


the rate law for an overall reaction that occurs in a series of steps is determined

by the slowest step


when a reaction has reached a state of dynamic equilibrium

the reactants are being consumed at the same rate the products are being produced


writing the law of mass action

-the square brackets mean that the concentration is expressed in M
-the only information needed is a balanced chemical equation of the chemical reaction of interest


the magnitude of the eq constant K

if K is aprox. equal to 1 the forward reaction proceeds about half way


if the coefficients in a balanced chemical equation are mult. by a factor, the eq constant of the equation is

the original eq constant raised to the power of the factor mult to the balanced chemical equation


what will change the value of the equilibrium constant K

changing the temperature


reaction quotient Q

-the value Q relative to K is the measure of the progress of a reaction towards equilibrium
-its mathematical expression has the same form of that as K
-when Q=K the reaction is at equilibrium


factors that will shift the position of equilibrium

-temperature change
-pressure change
-concentration change

***a catalyst will not affect the equilibrium