Chemical Kinematics Flashcards
A change in gibbs free energy does what?
Determines whether or not a reaction is spontaneous .
What do chemical mechanisms propose?
A series of steps that make up the overall reaction.
What are intermediates?
molecules that exist within the course of a reaction, but are neither reactants nor products overall.
What is the are the rate determining steps?
They are the slowest step, also known as the max rate at which a reaction proceeds.
What is the collision theory?
States that a reaction rate is proportional to the number of effective collisions between reacting molecules.
rate = Z x f Z is the number of collisions and f is the fraction of collisions that are effective.
What is required for a collision to be effective?
The molecules must be in the proper orientation and have sufficient kinetic energy to exceed the activation energy.
What is the Arrhenius equation?
It is a mathematical way of representing collision theory
k=Ae^(-Ea/RT) k is the constant rate of a reaction, A is the frequency factor, and Ea is the activation energy of the reaction, R is the ideal gas constant, T is the temp in kelvin.
What is the transition state theory?
States that molecules form a transition state or activated complex during a reaction in which the old bonds are partially dissociated and the new bonds are partially formed. From the transition state, the reaction can proceed towards products or revert back to reactants. The transition state is the highest point of a free energy reaction diagram.
What factors affect reaction rates?
- increasing the concentration of reactant will increase reaction rate (except for zero-order reactions) because there are more effective collisions per time.
- increasing temp will increase reaction rate because the particles’ kinetic energy is increased.
- changing the medium can increase or decrease reaction rate, depending on how the reactants interact with the medium.
- Adding a catalyst increase reaction rate because it lower the activation energy. Homogeneous catalysts are the same phase as the reactants; heterogeneous are a different phase.
How are reaction rates measured?
in terms of the rate of the disappearance of a reactant or appearance of a product.
Rate laws take the form of?
Rate=k[A]^x[B]^y
rate orders do not usually match stoich coefficients.
rate laws must be determined from experimental data.
What are zero order reactions?
They have a constant rate that does not depend on the concentration of reactant.
the rate of a zero order reaction can only be affected by changing the temp or adding a catalyst.
A concentration vs. time curve of a zero order reaction is a straight line; the slope of such a line is equal to -k
What are first-order reactions?
They have a non constant rate that depends on the concentration of the reactant.
A concentration vs time curve of a first order reaction is non-linear
The slope of an ln [A] vs time plot is -k for a first order reaction .
What are second order reactions?
They have . constant rate that depends on the concentration of a reactant.
A concentration vs time curve of a second order reaction is nonlinear.
The slope of a 1/[A] vs time plot is k for a second order reaction.
What are broken order reactions?
Those with non integer orders.
