EXTENT OF CHEMIcAL CHANGE Flashcards
equation for mean rate of reaction x2
what are the units
reactant used or product formed
divide by
time
-g/s or cm cubed/ second or mol/s
factors affecting rate of reaction x5
-conc. of reactants- higher con. of particles+ higher no. collisions per second so greater rate.
conc is proportional to r.o.r
-press of reacting gases- higher pressure means higher concentration of reactant particles
-s.a of solid reactants
particles in a solution react with SURAFCE particles of solid- more surface particles= higher frequency of collisions = higher rate of reaction
temp
-increases frequency of collisions and makes the collisions more energetic more particles can ovrcome activation energy barrier, particles collide more often as they have more kinetic energy so increase r.o.r
temp is proportional to r.o.r
presence of catalyst
COLLISION THEORY
-chemical reactions occur ONLY when
-what is activation energy
-rate of reaction determined by
.
-reacting particles collide w/ eachother w/ sufficient energy
-minimum amount of energy particles must have to react
-rate of successful collisions
a graph shows rate of reaction gradually slowing- describe why
-reactions initially rapid- large no. reactant molecules
large no. collisions per second
-over time reaction slows-bcse more reactants have been turned into products- less reactant molecules
smaller no. collisions per second
-reaction stops- all reactants have been turned into products,
or one reactant is limiting
no more collisions between reactant molecules
difference btwn high conc. and low conc. reaction
-higher conc=faster, steeper, higher no. collisions
-higher conc= more products bcse more ractants
what is a hypothesis
proposal that describes a fact or observation that MUST be testable
RP-5 the R.O.R and concentration-
your looking for turbidity- cloudiness
-put measuring cylinder w/ sodium thiosulfate solution on printed black cross
-add hcl and swirl
-start stopwatch
-look down from top and stop clock when cross no longer visible
-carry out again using lower conc. sodium thiosulfate solution
-repeat whole experiment and get mean values for each conc. of sodium thiosulfate
-do not include any anomolous results in mean
-problem w/ disappearing cross practical
-how to tackle this
-not reproducible- some people see the cross for longer than others- not get same results
-use same size printed cross
RP-5 R.OR- volume of gas produced by reaction
-put hcl in conical flask- attach to bung and delivery tube
-put delivery tube into container filled with water and upturned measuring cylinder filled w/ water over delivery tube
-add magnesium to hcl
-start stopwatch
-hydrogen gas produced trapped in measuring cylinder
-evry 10 seconds measure vol hydrogen gas in cylinder and continue till no more H2 made
-repeat using different concentrations of hydrochloric acid
RP-5 concentration and R.O,R-
what do both these reactions show us
why is this finding reproducible
the greater the concentration, the greater the rate of reaction
- shown in two different experiments, can be repeated under different conditions to get same result
how to investigate how s.a affects rate of reaction
-hydrochloric acid and marble chips containing calcium carbonate
-attach bung to delivery tube
-put delivery tube into container filled with water and upturned measuring cylinder filled w/ water over delivery tube
-carbon dioxide released
-measure volume of co2 with different surface areas of marble chips
-how can you more accurately measure vol of gas produced
-what is another way to investigate vol of gas produced to work out ror
use gas syringe-
.
-measure mass of gas lost using balance
-put cotton wool in mouth of flask- gas can escape- acid/liquid X splash out
-if acid splashed out, you get anomolous result
-as gas produced, mass decreases
effect of temp on rate of reaction
-what is activation energy
-minimum energy particles need to react
-what do catalysts do
-how
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why are they useful
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why X include catalyst in equation
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what do enzymes do
-change (increase) r.o.r but are not used up during reaction
-provide different reaction pathway that has lower activation energy
-(particles require less energy to cross the activation energy barrier,- more particles successfully collide per second)
-allow us to increase r.o.r w/out increasing temp- saves money
-can be reused
-not a reactant, not used up
.
act as biological catalysts- a catalyst in biological systems
-what is a reversible reaction-
-how do you change the direction of reversible reactions
-example of reversible reaction where changing conditions reverses reaction
-what is needed for forwards and for bacward reaction
the products can react to produce the original reactants
-Adjusting the conditions
To favour either the reverse /forward reaction
-ammonium chloride ⇌ ammonia + hydrogen chloride
—-> heat
<—–cool
reversible reaction that’s
endo —->
exo <—–
-explain why
hydrated copper sulfate ⇌ anhydrous copper sulfate + water
if heat is added, we are putting energy in, it’s endo, temperature of system decreases
ENDO= COLDER
-in reverse reaction, energy released, temperature of system increases, so it’s exo
EXO= HOTTER
what will ALWAYS happen to a reversible reaction in a closed system (prevents escape of product/reactant)
forward and reverse reaction happen at exactly the same rate- this is eqillibrium
What is Le Chatelier’s principle
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2NO2—>
……….<—— N2O4
what happens if we increase concentration of 2NO2
if a system is at equillibrium, and a change is made to ANY of the conditions…the system responds to counteract the change
the system is no longer at equillibrium
-concentrations of all substances change until equillibrium reached
-System will favour the …forward….. reaction
-More …N2O4…. will be produced till equillibrium reached
2NO2 ⇌ N2O4
forward is exo
reverse is endo
-what happens if temp is decreased
-equllibrium shifts to …….
-the forward/ back reaction is exo/endo
-system opposes the change
-by favouring the reverse / backwards reaction
-A smaller yield would be achieved
-equllibrium shifts to …….
what would happen to equillibrium when pressure is increased
N2 + 3H⇌ 2N2H3
what would happen when pressure decreased
H2 + O ⇌ 2HO
-count large numbers/ moles
-side with most moles has higher pressure
The amount of……….. increases / decreases
Because the equilibrium shifts to the…….
as there are ….. moles of gas
system opposes the change
by favouring the …… reaction
yield…….
-same no. of moles on each side, changing pressure has no effect on position of equillibrium
The conditions for reaction of ethene with steam
-what is made
65 atm
300 C
a catalyst.
ethanol made
equillibrium means
-The forward and backward reactions occur
-At same rate
-in closed system
-concentrations of the reactants + productsremain constant-
NOT SAME CONC. just CONSTANT
what is a closed system
-Nothing can enter
-no product/ reactant or anything else can leave the reaction vessel
