Chemistry - Chemical Equilibrium
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- 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