W9 Chemical Kinetics l and ll Flashcards
Factors Affecting Rate of Reaction
- Temperature of Reactants
- Concentrations of Reactants
- Chemical Nature of Reactants
- State of Subdivision of the
Reactants - Presence of a Catalyst
What is the transition state?
Highest energy on the energy
curve – transient state whereby molecules can return to reactants or proceed to form products
How do you measure rate of reaction?
Or initial ROR?
- Draw tangent and calculate the gradient (rise over run)
-Tangent at=0, this is initial rate of reaction
-Steepness of gradient is how fast the reaction
is progressing
What react in a single step reaction?
Involves one or two molecules,
ions or atoms
If the temperature is changed, does this affect k?
If the temperature is changed, the Rate of the Reaction changes and so k must change
What is the order of reaction?
The power to which the concentration of reactants must be raised to give a rate equation that describes the experimental data.
What is a Differential Rate Equation?
A rate equation where the rate of consumption of a reactant / formation of a product is written as a differential
Pseudo 1st Order Reaction
When rate= k [A][B]
In the presence of a large excess of B, the reaction appears to be 1st order, it is Pseudo 1st Order kinetics.
What are the units for rate?
moldm^-3^s-1or Pas^-1
What is meant by State of Subdivision of the Reactants?
Surface contact between two phases. Surface
area to volume ratio.
What does bimolecular and termolecular mean?
Bimolecular= Two reactants, one product
Termolecular= Three reactants, one product
Order of a Reaction vs Molecularity
Order of a reaction:
- Sum of the concentration terms on which the rate of reaction actually depends on
- Can be fractional
- Only be determined experimentally
- Order is for whole reaction
Molecularity of a Reaction:
- No of molecules that must collide with each other simultaneously to result in a reaction
- Always a whole number
- Can be calculated (add up molecules in slowest step)
- Only applies to the slowest step
What does a rate equation show?
The rate of the reaction at a particular instant during the reaction – Rates of reaction cannot be measured directly
Rate= -d[A]/dt=K[A]
What is experimental data?
Measurements of the concentration of a reactant or product at different times throughout the reaction
What is an integrated rate equation?
Shows how the concentration varies with time. It is derived from the differential rate equation. It is an expression linking concentration of reactant A at a particular time [A]t compared to the concentration of A at the start of the reaction [A]0 and the rate constant k.
ln[A]t= ln[A]0-kt
