Chapter 14 Flashcards
Reaction rate
Speed at which reactions take place
Rate= change in concentration A/change in time =
Conc A2- Conca1/ t2-t1= delta[A]/ delta T
Factors that affect reaction rates
1- physical state of reactants
2- reactant concentration
3- reaction temperature
4-presence of a catalyst
Physical state and reactants
-more readily reactants the more rapid they react
-homogenous reactions ( all gas and liquids ) often faster
-heterogenous involving solis are slower , increased if the surface area increases
Reactant relationship with concentrations
Increasing concentration increases the rate of reaction
Temperature relating to reaction rates
-temp goes up so does reaction rates
-kinetics is related to temp
-higher temp molecules move faster
Presence of a catalyst
Catalyst affect rate without being in the overall balance equation
Instantaneous rate
The slope of the curve at one point in time
Initial rate
The instantaneous rate at time zero
Rate Law
Rate= k[A]^m[B]^n
Rate constant
K, specific constant at a given temperature
What does M and N stand for in rate law ?
The reaction orders which are determined by the experiment
Reaction Order
Individual order - respect tot the reactant
Order of the reaction - sum of the exponents on the reactants
First order
Rate doubles when the [A] doubles
Rate = k[A]
Second order
The rate quadruples when [A] doubles
Rate= k[A]^2
Zero order
Rate doesn’t change when [A] doubles
Rate=K
Determining Concentration Effect on Rate
We keep every concentration constant except for one reactant and see what happens to the rate
Rate1. K[A1]^x[B1]^y
———= ———————-
Rate 2. K[A2]^x[B2]^y
Relationship of [A] with time first order reaction
Ln[A]= -kt + Ln[A]@
K= is the slope in a ln[a] vs time graph
Half life first order reactions
T1/2 = 0.693/k
Relationship of concentration and time in second order reactions
1/[A]= 1/[A]@ +kt
K= slope when 1/[A] vs time
Half life of second order reactions
T1/2=1/(k[A]@)
Zero order reactions relationship with K
[A]t=-kt+[A]@
Zero order directly proportional
Factors that affect reaction rates
-temperature
-frequency of collisions
-orientation of molecules
-energy needed for the reaction to take place (activation energy )
Temperature and rate
Temp goes up rate goes up
Frequency of collisions
More collisions more reactions
Orientation of Molecules
Aligning molecules properly can lead to chemical reactions
Activation energy
The minimum energy needed for a reaction to take place
Transition state
The organization of the atoms at this higher energy state
The lower the activation energy the faster the reaction
The relationship between rate constant and temperature
K=-Ea/RT + ln A
K2. -Ea. (1 - 1) Ln——- = —.* ——- K1. R. (T2 T1)
Mechanism
Is a series of stepwise reactions hat show how reactants become products
Reaction Mechanism
Reaction may account all at once or through see Rea discrete steps , known as elementary reaction or elementary process.
Molecularity
Of elementary reaction tells how many molecules are involved in that step of the mechanism
Rate determining step
The slowest one is the determining step
When the first reaction is the slowest step ?
It’s observed that the rate law of the slow step is the rate law of the overall reaction
Intermediates
NOT a reactant or product
NOT the transition state
Usually appears in the end of the products of first step and the reactants of the second step
Mechanism with a fast initial step
The reactants and the products of the first step are in equilibrium with each other so Ratef=Rater
Catalyst
Increases the rate of the reaction by decreasing the activation energy of the reaction
-homogenous
-heterogeneous
-enzymes
Homogeneous catalyst
Catalyst in same phase as reactants
Heterogenous catalyst
Catalyst in different phases than reactants
Enzymes
Protein molecules that catalyze biological reactions
