Department of Chemistry
CHM 1220/1225 Exam IV A Answers
1. a.
Concentration/amount of reactant:
Increase increases rate according to the rate law
Physical state of reactants:
Smaller particle size, faster reaction
Gases faster than aqueous or liquids which are faster than solids
Presence of a catalyst:
Speeds up reaction by providing a pathway with a lower Ea
–
b.
2. a.
€
b.
€
b.
+
–
Use one: pH, [H ], pOH, [OH ]
Acidic
pH
<7
+
–7
[H ]
> 1 x 10 M
pOH
>7
–
–7
[OH ]
< 1 x 10 M
nd
st
Neutral
=7
–7
= 1 x 10 M
=7
–7
= 1 x 10 M
–
a.
2 order in ClO2; 1 order in OH ; 3 order overall
2
–
b . Rate = k[ClO2] [OH ]
2
2
c. k1 = 1.2 x 10 /(M •s)
6.
a.
b.
7.
x = 0.0166; [N2] = [C2H2] = 2.2 M ; [HCN] = 3.3 x 10 M
2
Basic
>7
–7
< 1 x 10 M
<7
–7
> 1 x 10 M
rd
5.
8.
2
Kc = 6 x 10 (666); Qc = 7 x 10 ; Kc < Qc; So, the reactions proceeds reverse (to the left)
–2
The equilibrium mixture is primarily reactants (Kc < 10 )
–2
a.
b.
€
Vertical axis: potential energy
Horizontal axis: reaction progress
Reactants on left; products on right
Difference from reactants to transition state: 25 kJ/mol
Products are lower than reactants by 15 kJ/mol
Ea(reverse) = 40 kJ/mol
A catalyst speeds up a reaction by lowering the activation energy by providing a different reaction
pathway. (It can either be a surface for the reaction or be used and produced during the reaction.)
[SO2 ]2 [O2 ]
3. a. Kc =
; Kc = [O2 ]
[SO3 ]2
1
–4
Kc =
b.
= 3.27 x 10
2
(55.3)
4. a. HCl, HBr, €
HI, HClO4, H2SO4, HNO3; LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
€
€
−1 Δ[I− ] Δ[I3 ]
=
3 Δt
Δt
Ea =
524.4K • 462.9K • 8.314
61.5K
0.693
4
t1 =
= 2.75 x 10 s
k
2
J
• ln125.4
5
mol • K
= 1.59 x 10 J/mol
CHM 1220/1225
Exam IV A Answers
9.
[H3O+]
[OH–]
1.67 x 10
0.0600 M
–13
M
Page 2 of 2
pH
pOH
12.778
1.222
10.
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
The reaction shifts forward
The reaction shifts forward
No effect (this is a solid)
No effect (same amount of gas on each side)
The reaction shifts forward
H2Se Binary acid same group; Se is larger so the H–X bond is weaker
HClO Oxyacid, same #O; Cl has a higher electronegativity, so the H–O bond is more polar
HCl Binary acid same period; Cl has a higher electronegativity, so the H–X bond is weaker
–
+
H2PO4– Same X, sam #O’s; H2PO4 is less negative and can more easily lose the H ion
H2SeO4 Oxyacid, same X; More O’s, so H–O bond is more polar
Extra Credit:
–
11. a. H2PO4
b. The figure below illustrates the reaction of boron trifluoride with ammonia. Label the Lewis acid and the Lewis
base.
Lewis acid
BF3
Lewis base
NH3