Exam 4
Chem 1A
1. (24 pts.)
Multiple choice.
b.
c.
d.
@
d.
3Ol$ + 2CHTOH(g)+2CO2@)+ 2HrO(g)
HrQG)""HrO(l)
H2o(s)-Hrog)
O' (g) +2H2@) -r'2H'O(g)
Basedon ionic radii and charges,which of the following would havethe largestlattice energy?
G)
b.
c.
d.
(iv)
A Lewis structurein which there areno forrral chargesis preferred.
I"ewis sffuctureswith largeformal charges(+2;3 and/or-2,-3) ne preferred.
The preferredIrwis strucflre is one in which positive formal chargesareoo the
mact gleetranegativgatBm$,
None of the above
Whish of thp following proees$es
is endothermic?
a.
b'
(iii)
Circle the correctanswer.
Which of the following is a useful guidelinefor the applicationof formal charges?
For neutralmolecules:
@
(ir)
SrO.
NaF.
CaBrt.
CsI.
+7 - 7-+1 -l
+L
-l
''t-il -l
The numberof lone pairs in the CO, moleculeis?
a.
b.
c.
1.
2.
3.
.u -.e=9.
re) 4.
(v)
Which of the following pairs of atomswould form a polar covalentbond?
a'
Cl-Cl'
Ylen-Izclwr
b.
!a Cl'
icxl3
c\
Cr-Br'
Gt
(vi)
l{X} points
Showallwork to reeeivefullcredit!!
Watchunitsand signifieantfi.gures!!
(i)
;
November 10,2008
Dr. Somma
:dllL
P-cl.
What is thc formal chargeon the oxygex atom in NrO?
^.0(C e)
I
d.
*i
-2
; Nj;r"l-9'
The dipole momentof LiH is 1.964x 10-DC.trr,and the interatomicdistancebtween
2.(l}pts)
Li andH in this moleculeis 159,6pm. What is thepercentageionic characterin LiH?
(hint:first calculatethe ionic chnracterfor a 100 VoionizedLi* and Eion pair)
y=
Gn-
= ( r u ^ trt-'1C)(tsf6 */a''")
-t1
L ' ,r{- 24
/o
;or"lt
cLv'n'etP:t
I
J--
f4n"l
fa n^r5o,1
(*
l. 16(n lA -'C,n
y too?* = ------iTY t@?7, $q
,' I (t ''C ''q,
3. (14 pts.) A gascompanycharges$1.30for 15ff of naturalgas (CH4)measuredat 20"C and 1.0
afrn.The heatof combustionof methaneis AfIo*= -890.4kJ:
CHlg) + 2Or(g) '* CQzG) * n'Og;
Calculatethe cost of heating 200 mL of water (s*u*= 4.184 Ug t and 4nt*=1 gnl-) from 20'C to
100t. Assumethat only 5091o
of trc heatgeneratedby cornbustionis usedto heatthe water; the rest of
the heatis lost in the surroundings.
(hints:R = 0.0821L-atrnlnwl-K;1inch = 2.54cm)
4. (12 prs.)
At 25"C,the following heatsof reaetionareknown:
zclF(e) + O'(g) -* CIOzG)+ FOG)
2ClF (S) + 2or(g) * CIOzG)+ 3FrO(g)
2Fr(g + OrG)'* 2FzO(g)
= 167A kJ/mol
A11ooo
AHooo=341.4 kJ/mol
AHo* = - 43.4kJ/mol
At the sametemperature,calculatethe AHoooof the following reactio.n:
CIF(g)+F (g)*ClFs(B)
5. (12 pts.)
Alfoo = |
Draw all of the possibleresonancestrucfires for the moleculeNrOo.
lo-*K-fi'q
Ub,'" q
- '*/'tl
,'3
\,qJ
o
A
c)t
Lyl-l;l
r--\
o-t
|t".*-K?:
o"njI
lq,o
6. (14 pts.)
Caleulatethe energyreleasedin thereaction
Ca(s)+ CL(g)'* CaClz(s)
The heatof vaporizationof Ca(s)is 193 kJlmol, the dissociationenergyof CL(g) is 244 kJlmol, the
lattice energyof CaCL(s)is 2266kJlmol, the fust ionization energyof Ca(g) is 590 kJ/mol, the second
ionization energyof Ca(g) is 1140kJ/mol, andthe elecfronaffinity of atomic Cl(g) is -348 kJ/mol .
Draw stepby stepthe cycle of reactionsinvolved in the formation of CaClr(s).
Et*,Gt)'Z=
Ir
Co , o (q )+ |CI * C
T, *T,
Qg) t CXr-(
- oQEvS
='6F+
(S1ortl'{o)kT
A{i l,-t=
- zz(& t<.)
= nz5
zrH,*fe*(sfJ
(a-CI'2 (::1
+z('A{c')- t'r' (C^Crt)
o yr(c*)
*
r,@>
t't+4*fc{r(3t.
=
[[1,*f'c*(,1]
Ar\,,^
=
Lt - u ZzeAaJ)
o
t13Vs + z'rqbT + S4ouTrttL+oLT Z(-3qS
7. (12 pts.) For the reaetion below, write the skuctural formulas for all the reactantsand the
productsand determinethe Al{:
CrH6@)+ Cl, -* C,H,C|+ HCl(g)
Use for your calculationthe following bond energies(8.E.): B.E. C-C * 348 kJ/mol; B.E. C-H =414
kJimol;B.E.Cl-Cl =242 kJlmol;B.E.C-Cl =327 kJlmol;B.E.H-Cl =431 kJ/mol
H
\/
t:t
,.r-C^
C-',+
.\
(+
;i
+ Ct-C|
.f
{- RCt
----er*L* C-.i
{\
fi
l+
b.u{.,2^
: L- 11, U- C{ (q"4/' zvz)
for'^"0; C-C(( t+-Cf ( 321i ,{Ti)
+ z''tzLr/,-*!)- (st,
(Vr+ vTl,^,,,A,
L;(, bTl,^.< lt?) ,.J/-,,"(
+'{3)
=