Chapter 10 - reaction rates Flashcards
what is the rate of a chemical reaction in real terms
how fast a product is being made or how fast a reactant is being used up
what is the generalized equation for ROR
rate = change in concentration/time
what determines the rate of a reaction
the frequency of successful collisions
what determines if something is a successful collision
- correct energy, Ea or higher
- correct orientation
name the main 4 factors on ROR
concentration, temperature, surface area, catalysts
define activation energy
the minimum energy required for a reaction to take place
what are the two ways of measured ROR
- measuring formation of a product
- measuring removal of a reactant
how can ROR be measured for a gas release
- use a gas syringe, take the volume of gas at regular intervals
- use an upturned measuring cylinder and take vols at regular intervals
- plot graph and take grad
- OR measure loss of mass over time
how can ROR be measured for a precipitate
measure how long it takes for a cross underneath a container to no longer be visible where ROR is INVERSELY proportional to time
define what a catalyst is
“a catalyst is a substance that changes the rate of a chemical reaction without undergoing any permanent changes itself by providing an alternative reaction pathway with a lower activation energy”
how do catalysts increase ROR
they reduce Ea by providing an alternative reaction pathway
what is a homogenous catalyst and name an example of a reaction with one
a catalyst which is in the same physical state as the reactants, it reacts with the reactants to form an intermediate then breaks down again to form the products and reform the catalyst
e.g.
Cl*(g)
2O3(g), 3O2(g)
what is a heterogenous catalyst and give an example of a reaction with one
a catalyst which is in a different physical state to the reactants, it usually works by the reactants weakly bonding to its surface/ adsorbtion where the reaction takes place then they desorb from the surface after the reaction
e.g.
Fe(s)
N2(g) + 3H2(g) 2NH3(g)
why do reactions with catalysts tend to be more sustainble/ why are they used in industrial processes
- they reduce the energy required
- they can also reduce costs
- they make the reaction faster/more product can be made
- the catalyst isn’t used up
- reactions can take place at lower temperatures
what does the Boltzmann distribution represent
- the spread of molecular energies in gases
what are the labels of the axes on a Boltzmann distribution
y-axis = number of molecules with given energy x-axis = energy
how does the distribution change with temperature and what effect does this have
the peak moves down and to the right, thus given the area under the graph is finite, the shaded area increases, more particles have greater than or equal to the Ea and thus the FOSC increases so ROR increases
why does ROR increase with concentration
- there are more particles per given volume
- thus particles are more likely to collide
- this means FOSC increases so ROR increases
why does ROR increase with temperature
- the particles move faster so they are more likely to collide and more likely to collide with the Ea so FOSC increases
why does a catalyst increase ROR
- reduces Ea by providing an alternative reaction pathway
- more particles react >= Ea so FOSC increases
why does increases the S.A. of the reactants increase the ROR
- greater area for collisions to occur on/more available molecules
- increases FOSC
how does the Boltzmann distribution change with the addition of a catalyst
- the shaded line is drawn at a lower energy, more molecules have greater than or equal to the Ea
what what are some key features of dynamic equilibrium
- the rates of the forwards and backwards reactions are equal
- the concentrations of the reactants and products do not change
- there must be a closed system
state le chatalier’s principle
“when a system in dynamic equilibrium is subjected to an external change the system readjusts and the position of equilibrium changes to minimize the effect of that change”
