Chapter 5 - Chemical Kinetics Flashcards
what determines whether a reaction will occur without outside assistance?
the change in Gibb’s free energy
if a reaction is spontaneous, does that mean it will run quickly?
no
what is the mechanism of a reaction?
the steps a reaction takes to get from reactants to products
what is the sum of the mechanism of a reaction?
the overall reaction (equation)
what are intermediates of a reaction?
molecules formed in the middle of a mechanism but not present in the overall reaction, real molecule formed but may not be present for a long time
what is the rate determining step?
slowest step in a proposed mechanism, acts like a kinetic bottleneck, prevents overall reaction from proceeding any faster than the slowest step
what is the collision theory of chemical kinetics?
rate of reaction is proportional to the number of collisions per second between the reacting molecules
what makes a collision effective for a reaction to occur?
molecules must collide together in the correct orientation and with sufficient energy to break their existing bonds and form new ones
what is the activation energy?
minimum energy of a collision necessary for a reaction to take place
what is the equation for the rate of a reaction?
k= Ae^Ea/RT A= frequency factor Ea= activation energy R=ideal gas constant T= temp in kelvin
what happens as frequency factor increases?
rate increases
does reaction rate increases or decrease with an increase in temperature?
increase
how can the frequency factor be increased?
by increasing the number of molecules in a vessel
what is the transition state?
when molecules collide with energy greater than or equal to the activation state, they enter a state in which old bonds are weakened and the new bonds begin to form; will then dissociate into products, fully forming the new bonds, has greater energy than the products and reactants,
o Transition states are theoretical constructs that exist at the point of maximum energy, rather than distinct identities with finite lifetimes
o Can dissociate into products or revert back to reactants without any additional energy input
o Exist at peak of the energy diagram
what is the free energy change of a reaction?
difference between free energy of products and free energy of the reactants
what is an exergonic reaction?
negative change in Gibbs free energy
what is an endergonic reaction?
positive change in Gibbs free energy
what defines the activation energy?
Difference in free energy between the transition state and the reactants is the activation energy of the forward reaction, difference in free energy between the transition state and the products is the activation energy of the reverse reaction
what happens as the concentration of reactants increases?
reaction rate increases
what happens as temperature is increased
increases the reaction rate for nearly all reactions
why does increasing the temperature increase the reaction rate?
increases the average kinetic energy of the molecules
what will happen if the temperature is too high for a reaction?
catalyst may denature and then reaction rate will plummet
are all reactions temperature dependent?
yes, all reactions have a temperature for optimal activity
what properties of a medium can affect the reaction rate?
aqueous/nonaqueous, physical state (solid, liquid, gas), polar/nonpolar
what is a catalyst?
substances that increase the rate of a reaction without themselves being consumed in the reaction; Interact with the reactants and stabilize them to reduce the activation energy
what is a homogenous catalyst?
in same state (liquid, gas, solid) as the reactants
what is a heterogenous catalyst?
in a different state (liquid, gas, solid) as the reactants
do catalysts affect both the forward and reverse reactions?
yes, lowers activation energy for both
do catalysts affect equilibrium?
no
can catalysts affect spontaneity of a reaction?
no; No impact on the free energies of the reactants or the products of the difference between them ,Only make spontaneous reactions move more quickly towards equilibrium
