Reaction Kinetic(1) Flashcards
1
Q
Average rate
Instantaneous rate
Initial rate
A
- change in concentration of reactant or product over a time interval
- rate of change in concentration of reactant or product at a specific point of time
- instantaneous rate at time=0
2
Q
What is order of reaction
A
- order of reaction with respect to a given reactant is the power to which the concentration of the reactant is raised in the experimentally determined rate equation
3
Q
Rate constant, k
A
- is a constant of proportionality in a rate equation
- value is dependent on temperature and activation energy of the reaction and is not dependent on concentration of reactants
- unit of k depend on overall order of reaction
4
Q
Effect of temperature and catalyst on rate constant, k
A
- increasing temperature will increase value of k
- presence of catalyst lowers activation energy and increase value of k
5
Q
Zero order reaction
First order reaction
Second order reaction
A
- rate of reaction is independent of [A]
- rate of reaction is directly proportional to [A]
Rate of reaction is directly proportional to [A]2
6
Q
What is half life, t1/2
A
- is the time taken for concentration of a reactant to decrease to half its original concentration
- for first order reaction: half life is constant and independent on initial concentration of reactant
7
Q
Conditions for Pseudo first order reaction
A
- prescence of a large excess of a reactant
- reactant is also a solvent in the reaction
- presence of a catalyst
8
Q
What is the collision theory
A
- states that in order for a reaction to take place between two colliding reactant particles, particles must be correctly orientated, collision must occur with a minimum amount of energy called the activation energy
- collisions that fulfill both criteria are termed as effective collisions and increase in frequency of effective collisions lead to an increase in rate or reaction
9
Q
Factors affecting rate of reaction
A
- reactant particle size
- concentration of reactants
- pressure of gaseous reactants
- effect of temperature
- effect of catalyst
10
Q
How does reactant particle size affect rate of reaction
A
- for a fixed mass
- the smaller the size of reactants
- the larger the surface area exposed for reaction to occur
- frequency of effective collisions increases
- rate of reaction increases
11
Q
How does concentration of reactant affect rate of reaction
A
- increase in concentration of reactant causes
- an increase in number of molecules per unit volume
- frequency of effective collision increase
- hence rate of reaction increases
12
Q
How does pressure of gaseous reactants affect rate of reaction
A
- an increase in pressure of gaseous reactants
- larger number of molecules per unit volume
- frequency of effective collisions increases
- hence rate of reaction increases
13
Q
How does temperature affect rate of reaction
A
- increasing the temperature gives collisions more energy
- increases the frequency of effective collisions
- rate of reaction increases
- activation energy remains unchanged but rate constant k of reaction increases
14
Q
How does catalyst affect rate of reaction
A
- catalyst increases the rate of reaction rate by providing an alternative reaction pathway which has lower activation energy
- remains chemically unchanged at the end of the reaction
- does not affect the yield of reaction
- increases the rate constant, k for the reaction
15
Q
What is heterogenous catalysis and the different stages in heterogeneous catalysis
A
- exists in different phase from reactants
- adsorption of reactant molecules onto catalyst surface
- new bonds formed between reactant molecules
- desorption of product molecule from catalyst surface
16
Q
How does heterogenous catalysis speed up rate of reaction
A
- adsorption increases the concentration of reactant molecules at the catalyst surface and allows reactant molecules to come into close contact with proper orientation for reaction to take place
- the adsorption weakens the existing bonds within the reactant molecules, and lower the activation energy for reaction
17
Q
What is homogenous catalysis
A
- exists in same phase as reactants
- has various oxidation states
18
Q
What is autocatalysis
A
- involves the formation of a product that acts as a catalyst for the reaction
- product is known as auto catalyst
19
Q
Characteristics of autocatalysed reaction
A
- initially slow as it is not catalysed
- reaction rate increases upon formation of products and will reach maximum even as more of auto catalyst is formed
- reaction rate decreases due to decreasing concentration of reactants
20
Q
Thermodynamic stability vs Kinetic stability
A
- thermodynamics explains the tendency for a reaction to occur while kinetics gives an indication of rate at which this tendency is realised
