3.2.1 Rates of chemical reactions Flashcards
1
Q
rate of reaction
A
change in concentration of a reactant or product per unit of time
2
Q
how to measure rate of reaction
A
- how much reactant is used in a given time
- how much product is formed in a given time
- change in pH or colour
3
Q
collision theory
A
for a reaction to occur particles must:
- collide with each other
- collide with sufficient energy to break bonds within reactants
- collide with correct orientation to break bonds within reactants and allow formation of new products
4
Q
activation energy
A
minimum energy a collision must possess for a reaction to occur
5
Q
transition state
A
- stage of maximum potential energy (activation energy) where bond breaking and forming occur and atom arrangement is unstable
6
Q
what changes rate of reaction
A
- surface area of solid reactants (frequency)
- concentration of reactants in solution (frequency)
- pressure of gaseous reactants (frequency)
- temperature (frequency and energy)
- catalysts (energy)
7
Q
how to increase rate of reaction
A
- increase frequency and energy of collisions so more proportion of collisions between reactant particles have E>=Ea and correct orientation
8
Q
concentration/pressure
A
- more reactant particles moving randomly in a given solution increasing frequency of collisions
- to increase pressure, can decrease volume or increase amount of reacting gas
9
Q
surface area
A
- more particles are present at the surface and are available to react meaning frequency of collisions increases
10
Q
temperature
A
- average kinetic energy increases so average speed of molecules in system increases increasing frequency of collisions
- greater proportion of particles have E>= Ea so proportion of successfull collisions increases
11
Q
maxwell- boltzmann distribution
A
- shows range of kinetic energy of particles at given temp
- as temp increases total number of particles (area under graph) with E>=Ea increases
- adding catalyst lowers value of Ea
12
Q
catalyst definition
A
- increases rate of reaction by providing alternate reaction pathway and reducing activation energy of overall reaction
- not consumed and neither reactant or product
13
Q
catalyst
A
- greater proportion of collisions have E>=Ea since Ea is lower so bonds in reactants can be broken more frequently and greater proportion of successful collisions
14
Q
homogenous catalyst
A
same physical state as reactants and products
15
Q
heterogenous catalyst
A
- different physical state to reactants and products
- more easily separated from products, easier to reuse, able to be used at high temps
16
Q
solid catalysts
A
- solid particles on surface adsorb (form bonds with) gas molecules that strike the surface, distorting bonds in gas molecules or breaking them completely so reaction can occur
- powdered or sponge-like (porous) forms increase surface area and increases rate of reaction
