Speed Of Reaction Flashcards
rate/sor
is a measure of how fast or how slow a chemical change takes place
how 2 find sor?
- measure the time taken for a rctn to complete
- measure the vol of product formed per unit time
- measure the mass of reactant(s) used per unit time
vol of product formed per unit time
can only b used if one of the products formed is a gas
so thn u can find sor by measuring the vol of gas formed per min/at regular timed intervals-> stop taking readings whn u see consistent readings
1. grad of graph at the beginning: largest-> sor is the highest
2. grad of graph gradually decreases as rxn proceeds so sor decreases w time since thr r lesser reactants available
3. grad of graph bcomes 0-> graph bcomes horizontal meaning that no more gas is being produced and the rxn has stopped
the steeper the grad, the faster the speed n the lesser the time
mass of reactant(s) used per unit time
- grad of graph at the beginning: largest-> sor is the highest
- grad of graph gradually decreases as rxn proceeds so sor decreases w time since thr r lesser reactants available
- grad of graph bcomes 0-> graph bcomes horizontal meaning that rxn has stopped completely
the steeper the grad, the faster the speed n the lesser the time
collision theory
for a chemical rxn to occur, reacting particles must:
- collide w each othr
- collide w energy tht is = to or> than the Ea/Activation Energy
what are effective collisions?
collisions tht result in the formation of products & fulfill the collision theroy
increase in frequency of effective collisions=
increase in sor
factors tht affect sor
- particle size of solid reactants
- temp of reacting system
- pressure of gaseous rxns
- presence of catalyst
- conc of aq solution
effect of particle size on SOR
whn particle size ↓, SA(not SA:V!!!) of solid reactant ↑ so SOR ↑
when a solid reactant is broken up into smaller pieces
↓
total SA ↑
↓
as thr r more surfaces exposed for othr reactant particles to collide into/larger SA of contact btwn reactant particles
↓
the collision btwn the reactant particles become more
frequent
↓
↑ in frequency of effective collisions
↓
sor ↑
the intial gradient is the same for the graph the one that has a smaller particle size has greater gradient so sor is also greater however given the mass of the reactants used and the conc of the acid used etc stays constant n the only variable changed is the particle size, the the final volume of gas produced shld b the same
∴ particle size does not affect yield but affects sor
effect of temp on SOR
whn temp ↑ SOR ↑
at low temps, the reactant particles move SLOWLY bcos
thy hv little energy
↓
whn temp is ↑ed
↓
reactant particles gain more K.E.
↓
move faster
↓
more particles possess energy more than or equal to Ea
↓
↑ in frequency of effective collisions
↓
sor ↑
rmbr tht sor is inversely proportional to time!!
effect of pressure on SOR
pressure has very little effect on rxns involving only solids or liqs. however, in chemical rxns tht involve gases, changing pressure can significantly affect SOR
whn pressure of a gaseous rxtn ↑ SOR ↑
2 ways to increase pressure:
1. decrease the V, w same no of particles
2. increase no. of particles withn same V
higher pressure
↓
particles are closer together
↓
greater no. of particles in contact w one another
↓
↑ in frequency of effective collisions
↓
sor ↑
PRESSURE WILL NOT AFFECT YIELD OF NON-REVERSIBLE RXNS, BUT IT AFFECTS YIELD OF REVERSIBLE RXNS LIKE HABER PROCESS!
definition of catalyst
is a substance which increases the speed of a chemical rxn n remains chemically unchanged at the end of the rxn
characteristics of a catalyst
- only a small amt of catalyst is req to speed up a rxn
- a catalyst lowers the Ea of a rxn
- increases the speed but not the yield of a chemical rxn(same amt of products formed)
- the physical appearance of a catalyst may change at the end of the rxn, BUT its CHEMICAL properties remain unchanged(chemically unchanged)
- it is NOT used up during the rxn, same amt will b present in the beginning n at the end of the rxn
- impurities can prevent calatalysts frm working: catalyst is poisoned/ inactivated by impurities
- a catalyst is SELECTIVE in its action-> one catalyst cannot act on/speed up all types of rxns, diff catalysts speed up diff rxns-> thy r specific in thyr action
effect of catalysts on SOR
catalyst↑SOR by providing an alternative pathway for the rxn to proceed. the catalyst rxn has a lower Ea than the rxn w/o a catalyst
presence of catalyst
↓
provides an alternative pathway w lower Ea
↓
more particles posses energy more than or equal to
lowered Ea
↓
↑ in frequency of effective collisions
↓
sor ↑
enzymes- biological catalysts defintion
enzymes r substances tht catalyse chemical rxns in plants n animals (biological catalysts)
characteristics of enzymes
- they r proteins
- thy r specific in their actions: catalyse a specific chemical rxn
- sensitive to temp changes(many enzymes operate best at body temp 35-40 *C): abv the range denatured(unable to catalyze the rxn), below the range inactive
4, sensitive to pH changes(hv a certain range of pH at which thy work best
uses of enzymes
- manufacture of alcholic drinks:
the enzymes produced by yeast r used to catalyse the conv of sugar/starch into ethanol
sugar/starch –yeast—> ethanol + co2 - modern detergents/biological washing powders contain enzymes-> very effective in removing stains covered by protein-based substances such as food or blood
- biological catalysts r smtimes found in plants n animals: fluid in the cup of pitcher plants contain enzymes tht speeds up the dissolving of insects which fall into them
effect of conc on sor
whn the conc of a reactant ↑ SOR ↑
just like pressure in gaseous rxns conc is for liq rxns
more concentrated solution
↓
more reactant particles per unit volume
↓
↑ in frequency of effective collisions btwn particles
↓
sor ↑
affects yield as well! yield of LR increases w increased conc!!
