EXTENT OF CHEMIcAL CHANGE

Question 1

equation for mean rate of reaction x2
what are the units

Answer 1

reactant used or product formed
divide by
time
-g/s or cm cubed/ second or mol/s

Question 2

factors affecting rate of reaction x5

Answer 2

-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

Question 3

COLLISION THEORY
-chemical reactions occur ONLY when
-what is activation energy
-rate of reaction determined by

Answer 3

.
-reacting particles collide w/ eachother w/ sufficient energy
-minimum amount of energy particles must have to react
-rate of successful collisions

Question 4

a graph shows rate of reaction gradually slowing- describe why

Answer 4

-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

Question 5

difference btwn high conc. and low conc. reaction

Answer 5

-higher conc=faster, steeper, higher no. collisions
-higher conc= more products bcse more ractants

Question 6

what is a hypothesis

Answer 6

proposal that describes a fact or observation that MUST be testable

Question 7

RP-5 the R.O.R and concentration-
your looking for turbidity- cloudiness

Answer 7

-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

Question 8

-problem w/ disappearing cross practical
-how to tackle this

Answer 8

-not reproducible- some people see the cross for longer than others- not get same results
-use same size printed cross

Question 9

RP-5 R.OR- volume of gas produced by reaction

Answer 9

-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

Question 10

RP-5 concentration and R.O,R-
what do both these reactions show us
why is this finding reproducible

Answer 10

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

Question 11

how to investigate how s.a affects rate of reaction

Answer 11

-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

Question 12

-how can you more accurately measure vol of gas produced
-what is another way to investigate vol of gas produced to work out ror

Answer 12

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

Question 13

effect of temp on rate of reaction
-what is activation energy

Answer 13

-minimum energy particles need to react

Question 14

-what do catalysts do
-how
.
.
.
.
.
.
why are they useful

.
why X include catalyst in equation
.
.
what do enzymes do

Answer 14

-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

Question 15

-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

Answer 15

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

Question 16

reversible reaction that’s
endo —->
exo <—–
-explain why

Answer 16

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

Question 17

what will ALWAYS happen to a reversible reaction in a closed system (prevents escape of product/reactant)

Answer 17

forward and reverse reaction happen at exactly the same rate- this is eqillibrium

Question 18

What is Le Chatelier’s principle
.
.
.
2NO2—>
……….<—— N2O4

what happens if we increase concentration of 2NO2

Answer 18

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

Question 19

2NO2 ⇌ N2O4
forward is exo
reverse is endo

-what happens if temp is decreased

Answer 19

-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 …….

Question 20

what would happen to equillibrium when pressure is increased
N2 + 3H⇌ 2N2H3

what would happen when pressure decreased
H2 + O ⇌ 2HO

Answer 20

-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

Question 21

The conditions for reaction of ethene with steam
-what is made

Answer 21

65 atm
300 C
a catalyst.
ethanol made

Question 22

equillibrium means

Answer 22

-The forward and backward reactions occur
-At same rate
-in closed system
-concentrations of the reactants + productsremain constant-
NOT SAME CONC. just CONSTANT

Question 23

what is a closed system

Answer 23

-Nothing can enter
-no product/ reactant or anything else can leave the reaction vessel