kinetics Flashcards
(22 cards)
define: activation energy
the minimum amount of kinetic energy particles must collide with to break existing bonds in the reactant particles and start a reaction
draw the reaction profile for an exothermic reaction
pic
draw the reaction profile for an endothermic reaction
pic
what do the maxwell-boltzmann distribution curves show?
the distribution of the energies of the particles in a gas
what are the four main about the maxwell-boltzmann distribution curves to note?
- there are no particles with zero energy
- the curve does not touch the x-axis at the higher end
- the area under the curve is equal to the number of particles in the system
- the peak of the curve indicates the most probable energy of any particle
what particles can react when a collision occurs?
only the particles with energy equal to or greater than the activation energy
in this picture, which temperature is higher?
pic
T2
how does temperature affect the rate of reaction?
at higher temperatures, particles move faster and
therefore there is a large increase in the number of particles with higher kinetic energies
which results in a large increase in the rate as there will be more frequent successful collisions
why does even a small increase in temperature increase the rate?
because there are a greater number of particles with energy greater than the activation energy
what effect does concentration have on the rate of reaction?
increasing the concentration of reactants in a solution will result in particles being closer together
and so there will be more frequent collisions and more chances for particles to react
what effect does increasing the pressure of gaseous particles have on the rate?
increasing the pressure will result in the gas particles being closer together
and so there are more frequent successful collisions
and so a faster rate of reaction
define: catalyst
a substance that alters the rate of a chemical reaction but is unchanged itself at the end of a reaction
does not get used up
how do catalysts work?
by providing an alternative reaction pathway that has a lower activation energy
does a catalyst alter the maxwell-boltzmann distribution curve?
no
what affect does catalysts have on the proportion of particles?
because it provides a route with a lower activation energy,
there will be a greater proportion of particles with greater energy than the activation energy
why are catalysts useful?
because a catalyst increases the rate of reaction without being used up its cheaper than increasing the temperature or concentration
what happens if the frequency of collisions is increased?
the rate of reaction will increase
what can be done to increase the frequency of collisions
by increasing:
- the concentration of the reactants in solution
- the temperature
- the surface area of a solid reactant
- the presence of a catalyst
what does increasing the concentration of a solution do to the rate?
increasing the concentration of a solution increases the number of reactant particles per unit volume
and so increases the probability of productive collisions between reactive particles
this change increases the reaction rate
what does increasing the pressure of a gaseous reactant to to the rate?
if the pressure of a gas is increased, the particles in the gas are pushed closer together
this increases the concentration of the gas
and so the rate of collisions is increased
what does increasing the surface area of a solid reactant do to the rate?
if more surface is exposed then there is a greater surface area available for collisions
and so a faster rate of reaction
what does increasing the temperature of the reaction do to the rate?
particles have more energy at higher temperatures
so they move about more quickly
and so there are more frequent successful collisions
and so a faster rate of reaction
