Kinetics and Equilibrium Flashcards
What is Chemical Kinetics?
The study of the factors which affect the rate of a chemical reaction.
Define the rate of a chemical reaction.
It is either the increase in the concentration of one of the products per unit time or the decrease in the concentration of on of the reactions per unit time.
When does the chemical rate decrease?
Rates of reaction decrease with time as the reactants are used up.
Describe the collision theory.
For a reaction between two particles to occur two conditions must be met. The particles must not only collide so that the reactive parts of the particles come into contact with each other, but they must collide with sufficient energy to bring about the reaction. This minimum amount of energy required is known as the activation energy. Any factor that either increases the frequency of the collisions of increase the energy with which they collide will make the reaction go faster.
What is the activation energy?
The particles must collide with sufficient energy to bring about the reaction. This minimum amount of energy is known as the activation energy.
What can make a chemical reaction go faster?
Any factor that either increases the frequency of the collisions or increases the energy with which they collide will make the reaction go faster.
Explain the rate determining step
- When there are more than two reactant molecules, the reaction does not go in one step.
- When there is more than one step then each step will proceed at its own rate i.e. some steps are fast and other steps are slow.
- The overall rate of the reaction will depend only upon the rate of the slowest step.
- This slowest step is known as the rate determining step.
Describe the factors which affect the rate of reaction.
There are four factors which affect the reaction:
- Temperature
- Surface area
- Concentration
- Catalyst
What is the rate constant?
The rate constant is the constant of proportionality.
What is the half-life?
The half-life is defined as the time when the concentration of a reactant has a fall to half of its initial value.
Describe When Arrhenius Equation.
- The rate constant for a reaction is only constant if the temperature remains constant.
- As the temperature increases the reactants possess more activation energy and the rate constant increases.
- The relationship between the rate constant and the absolute temperature is known as Arrhenius equation.
Define dynamic equilibrium. What is the rate of the forward and the reverse reactions at equilibrium?
In a closed system the concentrations of all the reactants and products become constant. Such a system is said to be in a state of Dynamic Equilibrium. At equilibrium the rate of the forward reaction is equal to the rate of the reverse reaction.
Give an example of dynamic equilibrium when physical changes take place.
Closed flask with water, equilibrium will be reached between the liquid water and the water vapour. The faster moving molecules in the liquid will escape and become vapour and the slower moving molecules in the vapour will condense back into liquid. Equilibrium will be established when the rate of vapourization equals the rate of condensation.
H2O (l) ->
What is the closed system? Why would never equilibrium be reached if the system is open?
Closed system: A system is called a closed system in which neither matter nor energy can be lost or gained from the system. If the system is open, some of the products from the reaction could escape.
Therefore, in an open system equilibrium would never be reached.
Explain Le Chatelier´s principle. Write down the general formula.
It states if a system at equilibrium is subjected to a small change, the equilibrium tends to shift so as to minimize the effect of the change.
A + B ->
