Lecture Twenty - Reaction kinetics Flashcards
Distinguish between kinetics with equilibrium.
A rapid reactions does not necessarily mean that it goes to completion.
Could have a fast reaction which still has a small K value.
Kinetics tells us the speed or rate of the reaction and its mechanism.
- Rate = the change in concentration of reactants or products as a function of time.
- Often stepwise.
What are the factors which can affect the rate of a reaction?
Concentration of reactants.
Physical states of the reactants - solid, liquid, gas or aqueous.
Temperature (K).
The use of a catalyst.
How does the concentration of reactants affect the reaction rate?
Two substances cannot react without coming into contact with one another, if there is no contact the rate of the reaction is zero.
The more reactant particles that collide per hit time, the more often a retain will occur.
The rate of reaction usually increases as the concentration of reactants increases.
How does the physical state of the reactant affect the reaction rate?
For a heterozygous reaction, the (reactants in two different phases) collisions between the reactants can occur only at the interphases between phases.
Number of collisions between the reactants per unit time depends on the surface area of the more condensed phase. The higher the SA, the faster the reaction rate.
How does temperature affect the reaction rate?
Increasing the temperature of a system increases the average kinetic energy of its constituent particles.
As the average KE increases, particles move faster and collide more frequently with greater energy, causing increases int he rate of the reaction.
How do catalysts affect the rate of chemical reactions?
A catalyst is a substance that participates in a chemical reaction and increases the rate of there exaction without undergoing a net chemical change itself.
Catalysts are highly selective and often determine the product of a reaction by accelerating only one of several possible reactions that could occur.
Do all particles in a solution possess the same kinetic energy?
No, there is a curve that describes the distribution of the kinetic energies of the particles in a solution, called the Boltzen distribution curve.
Define and describe reaction rates.
Reaction rate = the change in concentration of a reactant or product over time.
How can mole ratios effect reaction rate calculations?
How is the average reaction rate calculated?
Y2-Y1/X2-X1.
Just as in maths, take two points between the point where you want the rate, and subtract the bigger from the smaller.
How is instantaneous reaction rate calculated?
Use rise over run.
What are the rate laws?
n is the reaction order, the degree to which the rate of the reaction depends on the concentration of each reactant.
n is not related to the stoichiometric coefficients int he balanced chemical equation but must be determined experimentally.
n can be 0, an integer or a fractional value.
k is the rate constant for the reaction.
k is characteristic of the reaction and the reaction conditions.
Units of k vary with the order of the reaction, that is, k depends on n.
