Topic 16 Flashcards
Define rate of reaction
Change in concentration of a substance per unit time
Units of rate equation
Normally mol dm-3 s-1
Define rate equation
The relationship between the rate of a chemical reaction and the concentration of reagents
Define rate constant
Relates the rats of a chemical reaction at a given temperature to the product of the concentration of reactants
What does order with respect to a substance in a rate equation mean
- It tells you how the reactants concentration will affect the rate of reaction.
- In the rate equation, it is the appropriate power to which the concentration of the reagent is raised
Overall order of reaction
Sum of all the individual orders of all the reactants in a chemical reaction
Half life
- Time taken for initial amount of reactant to decrease by a half
- Constant for first order reactions
Rate determining step
- The slowest step in a multi-step reaction
- Overall rate is decided by this step
- species occurring in the RDS will also occur in the rate equation
Define activation energy
Minimum amount of energy needed by particles to react
Heterogeneous catalyst
- Catalyst in a different phase from the reactants.
- Used in gas phase reactions to provide surface for the reaction
Example of a heterogenous catalyst
Hydrogenation of alkenes (gaseous substrates) is catalysed by a transition metal (solid)
Homogenous catalyst
- Catalyst in the same physical state as reactants
- Usually aqueous
Example of homogeneous catalyst
Acid catalysed esterification
Two equations that show the conversion of SO2 and O2 into SO3 by using V2O5 as a catalyst
- SO2 + V2O5 —> SO3 + V2O4
- V2O4 + 1/2 O2 —> V2O5
Two equations to show the reaction between persulphate ions and iodide ions using iron as a catalyst
- S2O8(2-) + 2Fe(2+) —> 2SO4(2-) + 2Fe(3+)
- 2Fe(3+)
Zero order
-Concentration of species has no impact on rate
-Rate/ time graph has gradient of zero
-Concentration/ time graph is linear
-Rate=k with respect to species
First order
-Concentration of species is directly proportional to rate
-Rate/ time graph is linear (doubling conc. doubles rate)
-Concentration/ time graph is curved
-Rate=k[A] with respect to species
Second order
-rate is proportional to concentration squared
-Rate/ time graph is exponential (doubling conc. quadruples the rate)
-Concentration/ time graph is curved
-Rate=k[A]^2 with respect to species
