5. Chemical Kinetics DONE Flashcards
What is Gibbs Free energy ?
determines whether or not a reaction is spontaneous.
If it is positive, it is not spontaneous, if it is negative, it is spontaneous.
Google: The Gibbs free energy is the available energy of a substance that can be used in a chemical transformation or reaction. Substances tend to transform into other substances that have less Gibbs free energy. The change of Gibbs free energy predicts whether a chemical reaction will occur spontaneously.
What are chemical intermediates?
They are molecules that exist within the course of a reaction but are neither reactants nor products at the very beginning or end.
What is the collision theory?
states that a reaction rate is proportional to the number of effective collisions between the reacting molecules
For a collision to be effective, molecules must be in the proper orientation and have sufficient kinetic energy to exceed the activation energy
T/F: in the collision theory, all collisions result in chemical reactions.
False, they must have enough kinetic energy
What is the Transition state theory?
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 toward products or revert back to reactants.
This occurs at the very tip of the graph.
In the energy diagram, where is the transition state?
It is the highest point
In the reaction/energy diagram, what parts are the:
Free energy change of the reaction
Negative Free energy
Positive Free energy
Transition State
Activation energy
Free energy Change of the Reaction (∆Grxn) is the difference between the free energy of the products and the free energy of the reactants.
Negative free energy represents a exergonic reaction
Positive free energy represents endergonic reaction (energy is absorbed)
Transition State: at the Peak of the diagram
Activation Energy: difference between free energy between the transition state and the reactants in the the reaction going forward. The activation energy going reverse tis the difference in free energy between the transition state and the products.
What is the difference between Homogenous and heterogeneous catalysts?
Homogenous catalysts are the same phase as the reactants.
Heterogeneous Catalysts- are in a different phase.
What are ways that you can increase the reaction rate? (x4)
- Increase the concentration (except in zero order reactions)
- Increase the temperature (they have more energy)
- Change the medium (depending on molecule)
- Add a catalyst
Why would increasing the concentration of a molecule increase the reaction rate?
Increasing the concentration will increase the reaction rate (except for zero-order reactions), because there are more effective collisions per time
If in a gaseous state, you would increase the partial pressure to increase the concentration.
Why would increasing the temperature of a molecule increase the reaction rate?
Increasing the temperature will increase reaction rate because the particles’ kinetic energy is increased.
Why would changing the medium of a molecule increase the reaction rate?
Changing the medium can increase or decrease reaction rates, depending on how the reactants interact with the medium.
For example, polar solvents are preferred because their molecular dipole tents to polarize the bonds of the reactants, lengthening and weakening them, and allowing the reaction to occur faster.
Why would adding a catalyst increase the reaction rate?
Adding a catalyst increases reaction rates because it lowers the activation energy.
Describe in words what is happening in the this two step mechanism.
Two molecules of A2B come together in a combination reaction to form an intermediate, A4B2, which subsequently decomposes to produce the final products. Two molecules of A2 and one molecule of B2
Molecule A4B2 is the intermediary.
What does it mean for a step in a mechanism to be the rate determining step?
The rate-determining step is the slowest step of a reaction. It determines the overall rate of the reaction because the reaction can only proceed as fast as the rate at which this step occurs.
What is the Rate law Equation?
k= proportionality constant
Exponents= order of the reaction (x, y or z)
Overall order of the sum of x and y
TRAPS!
The values of X and Y do not represent the stoichiometric coefficients product concentrations do not appear in the rate law
The rate law is NOT the equilibrium constant expression. The rate law instead tells how fast you will get to the equilibrium concentration. They are not the same.
The reaction rate is generally measured at the beginning of a reaction, the equilibrium concentration is usually measured at the end of the reaction.
What are zero order reactions?
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 temperature 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
If you double the reactant, the rate will not change.
What are First order reactions?
have a non-constant rate that depends on the concentration of reactant (at least one).
A concentration vs. time curve of a first-order reaction is non-linear
Determine the rate law and rate order for the following reaction…
Describe the effects the following conditions would have on the initial rate of reaction, given the reaction order (examples: rate increased, rate divided by 2, rate unaffected).
