Rates Flashcards
Define half-life.
The time for the concentration of one of the reactants to fall by half.
Define the rate of reaction.
The change in concentration (removal) of a reactant or (formation) of a product divided by time.
Define the rate determining step.
The slowest step in a multi-step reaction: the one with the highest activation energy.
define catalyst.
‘A substance which speeds up a chemical reaction by providing an alternative reaction pathway of lower activation energy without undergoing any PERMANENT change itself.’
define activation energy.
The energy barrier that must be overcome before a reaction can occur.
Where are homogenous catalysts frequently found?
The action of enzymes in biological systems.
Why does increasing the surface area increase the rate of reaction?
Increasing the surface area increases the chance of a collision taking place, particles can only react if they collide.
Define the overall order of a reaction.
The sum of the powers to which
concentration terms are raised in the overall rate equation.
what happens to the half life of a second order reaction as the concentration of the reactant halves?
It doubles.
define order of reaction with respect to a reactant.
the power to which the concentration is raised in the rate equation.
At a higher temperature, what do particles have more of?
Kinetic energy.
What use is quenching a reaction?
Prevents further change in concentration of a substance PRE analysis. Either add to cold water ([reactants] GREATLY decreases + reaction effectively stops (cold helps slow)) OR add to a soln which removes a reactant + do a back titration.
In an iodine propanone expt why is the [propanone] much larger than [I2]?
To ensure the [propanone] remains effectively constant during the experiment so the only MEASURABLE change in [ ] is that of the I2.
How do heterogenous catalysts often work?
Reactant molecules are ADSORBED onto (metal) surface - weakens bonds between atoms in reactant molecules, reducing Ae of reaction.
why are transition metals often used as catalysts?
They have variable oxidation states + can alter no. of bonds available to reactants.
