Kinetic Flashcards
What is the rate of an equation?
How quickly the concentrations of reactants and products are changing
mathematically described as the rate of change of [A] with respect to time: d[A]/dt
How to determine rate of reaction at time t?
Gradient of tangent to the graph at time t
d[A]/dt = -kt (negative so reactant used)
d[B]/dt = kt (positive so product formed)
What is instantaneous rate?
Rate at a specific moment in time
Units of rate?
Rate of change of concentration of a reaction or product with time
moldm-3s-1
Rate law?
Rate = k[A]a[B]b
What is an elementary reaction?
A single step process that involves one or two molecules
Two important features of elementary reactions?
Equation describe what is actually going on at the molecular level, for a complex reaction which is made up of elementary reactions the equation only gives the stoichiometry
For an elementary reactions it is possible to use the chemical equation to form the rate equation but this is not the case for complex reactions
Rate equation form elementary reaction?
An elementary reaction is a reaction that takes place at the molecular level ie what is really happening. The stoichiometric equation represents the overall reactions in terms of initial reactants and final products but does not show how a reaction actually happens, the molecularity of an elementary reaction is the number of molecules that come together to react
Unimolecular?
1 molecular involves eg isomerisation ot radioactive decay
Bimolecular?
2 molecules react
What is a reaction mechanism?
The sequence of elementary molecular events that lead from reactant to products, what happens at the molecular level during a chemical reaction from experimental determined kinetic data are used to postulate the mechanism for a reaction
Using the rate law to test a proposed mechanism?
Rate law is experimentally determined, we want to propose a reaction mechanism that accounts for the observed rate law, to do this we must be able to formulate the rate law that corresponds to the proposed mechanism and compare this with the experimentally observed rate law
What is the rate law?
Relates the concentration of reactants and the overall rate of reaction, empirically the rate of reactions is often but not always found to be related to the concentration of that reactant raised to a simple power
Rate constant k?
Rate constant k relates concentrations of reactants to the overall rate of reaction
Reaction order?
Power to which the concentration or pressure of a reactant is raised in the rate law, the order overall is the sum of order of reactant, until you have carried out experiments you cannot know that this is true, in general the rate law cannot be found from a chemical equation it must be found experimentally, order in an experimental observation depends on the mechanism of the reaction