reaction rates and equilibrium- chapter 10 Flashcards
what is the rate of a chemical reaction
measures how fast a reactant is being used up or how fast a product is being formed
what is the rate equation
change in concentration/time
when is the rate of reaction the fastest
at the start as each reaction is at its highest concentration
slows down as the reaction proceeds because the reactants are being used up and their concentration decrease
once one of the reactants have been completely used up, the concentration stops changing and the rate of reaction is zero
what factors change the rate of a chemical reaction
concentration
temperature
use of a catalyst
surface area of solid reactants
why does the rate change using the collision theory
as it states that two reacting particles must collide for a reaction to occur
when will a collision effective (2)
if the particles collide with the correct orientation
if the particles have sufficient energy to overcome the activation energy barrier of the reaction
how does increasing concentration affect the rate of reaction
when the concentration of a reactant is increased, the rate of reaction generally increases
as increase in concentration increases the number of particles in the same volume, the particles are closer together and collide more frequently
in a given period of time there will therefore be more effective collisions and an increased rate of reaction
how does increasing the pressure of a gas affect the rate of reaction
when a gas is compressed into a smaller volume the pressure of a gas is increased and the rate of reaction increases
the concentration of the gas molecules increases as the same number of gas molecules occupy a smaller volume
the gas molecules are closer together and collide more frequently, leading to more effective collisions
hwo is the progress of a chemical reaction followed
monitoring the removal (decrease of concentration) of a reactant
following the formation (increase in concentration) of a product
if a reaction produces gas, what are the two methods that can be used to determine the rate of the reaction
monitoring the volume of gas produced at regular time intervals using gas collection
monitoring the loss of mass of reactant using a balance
what is a catalyst
a substance that changes the rate of a chemical reaction without undergoing any permanent change itself
not used up
may react with a reactant to form an intermediate or may provide a surface on which the reaction can take place
at the end of reaction it’s regenerated
how does a catalyst increase the rate of a chemical reaction
providing an alternate reaction pathway of activation energy
what is a homogenous catalyst and how does it work
has the same physical state as the reactants
the catalyst reacts with the reactants to form an intermediate. the intermediate then breaks down to give the product and regenerates the catalyst
what is a heterogeneous catalyst
what happens to the reactants molecules
has a different physical state from the reactants, usually solids in contact with gaseous reactant in solution
they are absorbed (weakly bonded) onto the surface of the catalyst, where the reaction takes place. after reaction, the product molecules leave the surface of the catalyst by desorption
what are 3 features of the boltzmann distribution
no molecules have 0 energy- curve starts at origin
the area under curve is equal to the total number of molecules
there is no maximum energy for the molecule- the curve does not meet the x-acid at high energy. the curve would need to reach infinite to meet the x-axis
what is boltzmann distribution
the spread of molecular energies in gases
what is the effect of temperature on the boltzmanns distribution (higher temp)
- more molecules have an energy greater than than or equal to the activation energy
- therefore a greater proportion of collisions will lead to a reaction, increasing the rate of reaction
- collisions will also be more frequent as the molecules are moving faster, but the increased energy of the molecules is much more important than the increased frequency of collisions
what is the effect of a catalyst on the boltzmanns distribution
they provide an alternative reaction route with a lower activation energy
a greater proportion of molecules now have an energy equal to, or greater than the lower activation energy. on collision, more molecules will react to form products
the result is an increase in rate of reaction
