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33 Cards in this Set

  • Front
  • Back
What is the mechanism of a reaction?
It is the actual series of steps through which a chemical reaction occurs
What is the slowest step in a proposed mechanism called?
It is called the rate-determining step
What is rate?
For nearly all forward, irreversible reactions, the rate is proportional to the product of the concentrations of the reactants
What is the overall order of a reaction (reaction order) definsed as?
It is defined as the sum of the exponents, usually equal to x + y
What are zero-order reactions?
They have a constant rate, which is independent of the reactants’ concentrations
What is the rate law for a zero order reaction?
It is rate = k
What is a first-order reaction?
It has a rate proportional to the concentration of one reactant
What is the rate law for a first order reaction?
It is rate = k[A] or rate = k[B]
What is an example of a first order reaction?
Radioactive decay
What are second-order reactions?
It has a rate proportional to the product of the concentration of two reactants, or to the square of the concentration of a single reactant
What are some examples of a second-order reaction?
Rate = k[A]2, rate = k[B]2, or rate = k[A][B]
What are mixed-order reactions?
They have a fractional order, ie rate = k[A]1/3
What does the collision theory of chemical kinetics state?
It states that the rate of a reaction is proportional to the number of collisions per second between the reacting molecules
What is an effective collision?
It is one that leads to the formation of products
When does it occur?
It only occurs when the molecules collide with correct orientation and sufficient force to break the existing bonds and form new ones
What is the minimum energy of collision necessary for a reaction to take place called?
It is called the activation energy, or the energy barrier
What is a transition state?
It is when the old bonds are weakened and the new bonds are beginning to form
What is a transition state also called?
An activated complex
What is the enthalpy change of the reaction?
It is the difference between the potential energy of the products and the potential energy of the reactants
What does a negative enthalpy change indicate?
It indicates an exothermic reaction
When does the rate of reaction increase?
It increases if there is an increase in the number of effective collisions, or a stabilization of the activated complex compared to the reactants
How do reactant concentrations influence rate?
The greater the concentrations of the reactants, the greater the number of effective collisions per unit time, and therefore the reaction rate will increase for all but zero order reactions
How does temperature influence rate?
For nearly all reactions, the reaction rate will increase as the temperature of the system increases
How does the medium in which a reaction takes place affect rate?
The rate of reactions may also be affected by the medium. Certain reactions proceed more rapidly in aqueous solution, whereas other reactions may proceed more rapidly in benzene
How do catalysts work?
They increase reaction rate without themselves being consumed
What occurs in homogenous catalysis?
The catalyst is in the same phase as the reactants
What occurs in heterogeneous catalysis?
The catalyst is in a distinct phase
What is equilibrium?
It is when there is no net change in the concentrations of the products and reactants
What is the equilibrium constant?
Kc, is the concentrations of the products are divided by the concentrations of the reactants
What is Le Chatelier’s principle used for?
It is used to determine the direction in which a reaction at equilibrium will proceed when subjected to a stress, such as a change in concentration, pressure, temperature, or volume
What does change in concentration do?
Increasing the concentration of a species will tend to shift the equilibrium away from the species that is added
What does a change in pressure do?
It causes a change in volume
What does a change in temperature do?
If it is an exothermic reaction, and you add cold, the reaction would shift to produce heat