Kinetics & Equilibrium Review Packet
Standard Level
ANSWER KEY
1.
A
[1]
2.
C
[1]
3.
B
[1]
4.
B
[1]
5.
B
[1]
6.
D
[1]
7.
C
[1]
8.
C
[1]
9.
C
[1]
10.
C
1
[1]
2
11.
D
[1]
12.
C
[1]
13.
D
[1]
14.
C
[1]
15.
A
[1]
16.
A
[1]
17.
C
[1]
18.
D
[1]
19.
C
[1]
20.
C
[1]
3
21.
(a)
A;
E;
2
If 3 choices shown [1 max], if 4 choices shown [0].
(b)
(i)
after 15s (product) = 0.37 (mol dm–3);
rate = 0.37 = 0.025;
15
2 sig figs
(ii)
mol dm–3s–1/Ms–1/ M ;
sec
3
at equilibrium/rates of forward and reverse reactions are equal/∆G = 0;
1
[6]
22.
(a)
200°C 600 atm. (both for [1], units not needed);
allow the “highest pressure and the lowest temperature”
(b)
(i)
yield increases/equilibrium moves to the right/more ammonia;
2
4 (gas) molecules → 2/decrease in volume/fewer molecules on right hand side;
(ii)
yield decreases/equilibrium moves to the left/less ammonia;
exothermic reaction/OWTTE;
(c)
(d)
high pressure expensive/greater cost of operating at high pressure/reinforced
pipes etc. needed;
lower temperature – greater yield, but lowers rate;
Do not award a mark just for the word “compromise”.
Kc =
[NH 3 ] 2
[N 2 ][H 2 ]3
(ignore units);
1
2
2
1
[8]
4
23.
(a)
forward
Rate
reverse
Time
two curves – one labelled “forward” starting up high up y-axis and one labelled
“reverse” starting from zero;
curves merge and become horizontal;
No penalty for failing to label axes.
forward reaction:
highest concentration, thus rate high to begin with;
as reaction proceeds, concentrations decrease, so does rate;
(b)
reverse reaction:
zero rate initially/at t = 0 (since no products present);
rate increases as concentration of products increases;
equilibrium established when rate of forward reaction = rate of reverse reaction;
7
(reaction is) endothermic;
Kc increases with (increasing) temperature;
forward reaction favoured/heat used up/OWTTE;
3
[10]
24.
(a)
(b)
(position of) equilibrium shifts to the left/towards reactants; (forward)
reaction is exothermic/∆H is negative/the reverse reaction is
endothermic/OWTTE;
Do not accept “Le Chatelier’s Principle” without some
additional explanation.
2
(position of) equilibrium shifts to the right/towards products;
fewer gas molecules on the right hand side/volume decreases in forward
reaction/OWTTE;
Do not accept “Le Chatelier’s Principle” without some
additional explanation.
2
[4]
5
25.
(i)
( K c =)
[NO 2 ] 2
;
[N 2 O 4 ]
(horizontal line) concentration of reactant and product remains constant/equilibrium
reached;
(magnitude of) Kc greater than 1;
Accept 1.6.
(ii)
(iii)
(iv)
product concentration greater than reactant concentration;
4
increased temperature shifts equilibrium position to right;
(forward) reaction is endothermic/absorbs heat;
2
increased pressure shifts equilibrium to left;
fewer (gas) moles/molecules on left;
2
both/forward and reverse rates increased/increase in forward reverse
rates are equal;
activation energy reduced;
position of equilibrium unchanged;
concentration/amount of reactants and products remain constant;
value of Kc unchanged;
Kc only affected by changes in temperature;
6
[14]
26.
(i)
Number
of
molecules /
frequency
T1
T2
Ea
Energy
both axes correctly labelled;
T2 peak/lower;
and to right of T1;
Area under graph is not important.
3
6
(ii)
rate increased/changes;
as more molecules with ≥ Ea;
No explicit reference to graph required.
2
[5]
27.
(i)
CaCO3(s) + 2H+(aq) → Ca2+(aq) + H2O(l) + CO2(g)
States not required, accept molecular equation.
(ii)
rate decreases with time;
as concentration decreases so fewer (successful) collisions;
draw tangent to the curve at time t;
rate = slope or gradient;
1
4
(iii)
Volume of
CO2 produced
inal
orig
II
I
Time
I.
(less CO2 because) amount of HCl is limiting and half the
orginal/OWTTE;
II.
(same amount of CO2 because) amount of HCl is the same;
curve less steep because less frequent (accept fewer) collisions
Awarded last mark if in either I or II.
5
[10]
28.
(a)
(i)
(ii)
it is decreasing;
less frequent collisions/fewer collisions per second or (unit) time;
reactant(s) used up/reaction is complete;
Do not accept reaction reaches equilibrium.
2
1
7
(b)
(i)
it would increase;
Accept a quantitative answer such as “doubles”.
(ii)
more frequent collisions;
collisions or molecules have more
energy (OWTTE); more molecules with energy ≥ Ea;
3
rate would be lower;
smaller surface area;
2
(iii)
1
[9]
29.
(a)
measure volume of carbon dioxide/CO2/gas produced/measure pH;
4
starts at origin and levels off
measure mass of chemicals/apparatus;
starts high and decreases
Graph should show increase as reaction progresses
(as HCl is consumed).
8
(b)
Method 1
use powdered MgCO3/OWTTE;
particles collide more frequently/increased surface area/OWTTE;
Method 2
increase (reaction) temperature/heat/warm;
more of the collisions are successful/more particles with E > Ea/OWTTE;
Method 3
increase acid concentration;
more frequent (reactant) collisions;
Method 4
add catalyst;
lowers activation energy/Ea/OWTTE;
Award [2] each for any three methods
(c)
(i)
(ii)
6 max
stays the same;
MgCO3 was already in excess;
2
stays the same;
same quantities of reactants used;
2
[14]
30.
(i)
(ii)
(iii)
reversible reaction/reaction may proceed in either direction
(depending on reaction conditions) equilibrium/dynamic equilibrium;
1
no effect;
catalyst will speed up both forward and reverse reactions (equally)/
increase the rate at which equilibrium is achieved;
2
acidity: no effect;
equilibrium shifts to the right;
Kc: no change;
3
[6]
9