topic 6

rate of recations

most reactions are ….. at the beginning and then ….

fast, slow down

mean rate of reaction =

quantity of reactant used or product formed / time

how to find rate of reaction on curve graph

draw tangent, find gradient

for a chemical reaction to take place

particles must collide with enough energy to react

activation energy

minimum energy required for particles to react

why do reactions slow down

less reactant particles so less frequent successful collisions

why do reactions stop

no more particles of one of the reactants

higher concentration/ pressure of reactants in solution →

faster rate of reaction

why is reaction faster with more concentrated/ higher pressure reactants

particles closer together so more frequent successful collisons

relationship between rate of reaction and conc/pressure

proportional

larger SA of solid reactant →

higher rate of reaction

why does higher SA increase rate of reaction

more reactant particles on the surface- successful collisions more frequent

relationship between SA and rate of reaction

proportional

higher temp →

higher rate of reaction

why does higher temp = higher rate

particles gain kinetic energy so more frequent successful collisions

if temp doubles →

rate more than doubles as temp inc both frequency and success rate of collisions (not proportional)

why do catalysts not appear in overall chemical reaction equasions

not used up

how do catalysts work

providing different reaction pathway that has a lower activation energy

reversible reactions meaning

products can tun back into reactions

if forward reaction is exothermic, **backwards reaction is**

endothermic

if forward reaction has energy change of -75kJ, backwards reaction energy change =

\+75kJ

in **closed system**, reversible reaction can reach a state of

dynamic equalibrium

what is happening at equilibrium

both forwards and backwards reaction taking place simultaneously at the same rate

is position of equilibrium lies to the left

more reactants that products

is position of equilibrium lies to the right

more products than reactants

if a change is made to the conditions of a system at equilibrium

position of equilibrium moves to oppose the change

if temp inc, equilibrium moves in

endothermic direction to reduce temp

if temp dec, equilibrium moves in

exothermic direction to inc temp

if pressure inc, equilibrium moves

towards side with fewer gas molecules to reduce pressure

if pressure dec, equilibrium moves

towards side with more gas molecules to inc pressure

if conc inc, equilibrium reduces it by

doing more of the reaction that uses it up

if conc dec, equilibrium increases it by

doing more of the reaction that makes it