chapter 6: reaction kinetics ⏱ Flashcards
define activation energy
minimum energy which the colliding molecules must possess before a collision will result in a reaction
define rate of reaction
the change in concentration of reactant or product with time
define rate equation
experimentally determined equation that links the rate of reaction to the concentration of each reactants or catalyst to a specific power
define order of reaction
power to which the concentration of that reactant/catalyst is raised in the experimentally determine rate equation
define rate constant
proportionality constant in the rate equation
define rate determining step
slowest step in a reaction mechanism
define catalyst
substance which increases the rate of reaction by providing a different reaction pathway with a lower activation energy without itself going through any permanent chemical change
how to find instantaneous rate
gradient of tangent at time t
how to find initial rate
gradient of tangent at T=0
define half life
time taken for the concentration of a reactant to reduce to half of its initial value
what are the factors that affect the value of rate constant
- temperature
- addition of catalyst
why does an increase in concentration increase rate of reaction
when concentration of reactant increases,
- number of particles per unit volume increase
- increase frequency of effective collision
- acc. to collision theory, rate of reaction increases
why does an increase in temperature increase the rate of reaction
when temp. increases
- avg. KE of reactant molecules increase
- more molecules have higher energy
- more collision with energy greater than or equal to Ea
- frequency of effective collision increase
- rate of reaction increase
how does addition of a catalyst increase rate of reaction
- catalyst provides an alternative pathway with lower Ea
- more molecules have energy greater than or equal to lowered Ea
- frequency of effective collision increases
- rate of reaction increases
define heterogenous catalysis
exists in a different phase from reactants and increases rate of reaction by providing a different reaction pathway with a lower activation energy without itself undergoing permanent chemical change
explain the mode of action of heterogenous catalyst (first step)
reactant molecules are adsorbed on the active site of the catalyst via weak temporary bonds
explain the mode of action of heterogenous catalyst (second step)
reactant molecules are brought closer together, increasing their concentration at the catalyst surface
explain the mode of action of heterogenous catalyst (third step)
bonds in reactant molecules are weakened, lower Ea
explain the mode of action of heterogenous catalyst (fourth step)
molecules are orientated in the right position for reaction, increasing number of effective collisions
explain the mode of action of heterogenous catalyst (last step)
product is deserved from the catalyst surface, regenerating active site on the catalyst
define homogeneous catalysis
exists in the same phase from reactants and increases the rate of reaction by providing a different reaction pathway with a lower activation energy without itself undergoing any permanent change
why do the reaction of I- and S2O8 2- have high Ea
both reactants are negatively charged and they tend to repel each other
what does NO2 do
presence of small amounts of NO2 in the atmosphere can catalyse the oxidation of SO2 to SO3 by providing an alternative mechanism of lower Ea
when does autocatalysis occur
when product catalyses the reaction
