4.3 - Rates of reaction
No description yet. This curated deck is ready for daily study.
Card preview (24)
when can a chemical reaction only happen
if the reactant particles collide with enough energy
what is activation energy (Ea)
the amount of energy the particles need to react
what is the equation for rate of reaction
rate = collision frequency x percentage success
what does the overall rate of a reaction depend on
collision frequency - how often the particles collide with each other percentage success - what percentage of the collisions have enough energy
what are the factors that affect the rate of a reaction in terms of collision frequency and percentage success
solid surface area - collision frequency solution concentration - collision frequency temperature - percentage success catalysts - percentage success
why does higher solid surface area increase rate
-more of the solid is exposed to other particles - so the collision frequency is higher - so there are more successful collisions per unit time
why does higher solution concentration/ gas pressure increase rate
• there are more particles per unit volume • so the collision frequency is higher • so there are more successful collisions per unit time
why does higher temperature increase rate
• the particles have more kinetic energy • so the percentage of collisions with enough energy is higher • so there are more successful collisions per unit time
why do catalysts increase rate
• they provide an alternative route with a lower activation energy • so the percentage of collisions with enough energy is higher • so there are more successful collisions per unit time
for solutions and gases why does increasing the concentration or pressure increase the rate
• there are more particles per unit volume • so collision frequency is higher • so there as more successful collisions per unit time
how can you increase the concentration
dissolve more solute particles so there are more particles per unit volume
how can you increase the pressure
by making the reaction vessel smaller
what experiment explored the affect of concentration on rate
disappearing cross experiment
what can the effect of concentration on rate be demonstrated by
reacting sodium thiosulphate solution with hydrochloric acid
what is the chemical equation for reacting sodium thiosulphate with hydrochloric acid
Na2S2O3(aq) + 2HCl(aq) –> 2NaCl(aq) + S(s) + SO2(g) + H2O (l)
what is the input variable in the disappearing cross experiment
the concentration of the NaS2O3(aq)
what is the output variable in the disappearing cross experiment
the time taken for the cross to disappear
what are the control variables in the disappearing cross experiment
total volume of solution concentration of HCl (aq) temperature
what is rate calculated from in the disappearing cross experiment
time taken rate (S-1) = 1/ time taken
what would the graph for the disappearing cross experiment/ concentration effect on rate look like and why
would be proportional and show a straight line through the origin because the rate is proportional to concentration
for solids why does the surface area increase the rate
• more of the solid is exposed to the other particles • so the collision frequency is higher • so there are more successful collisions per unit time
how is increased surface area achieved
by cutting or grinding up the solid
what experiment explores the affect of surface area on rate
the marble chip experiment
what can the effect of surface area on rate be demonstrated by
reacting calcium carbonate chips with hydrochloric acid