SJCC
Chem.1A
Exam #3 (SAMPLE)
Prof. Song
Name:
For all numerical problems, show all your work and answer to correct no. of significant figures
for full credit.
1.
Given the following thermochemical data;
The standard heat of formation (ΔHf) for C6H6(l) = +48.6 kJ/mol,
ΔHf for CO2(g) = -393.5 kJ/mol, ΔHf for H2O(l) = -285.8 kJ/mol
Calculate the ΔH (in kJ) for the reaction,
2 C6H6(l) + 15 O2(g)  12 CO2(g) + 6 H2O(l)
2.
Given the following thermochemical data,
N2O4(g)  2 NO2(g)
NO(g) + ½ O2(g)  NO2(g)
H = 57.2 kJ
H = -57.0 kJ
Calculate the standard heat of reaction (H) for the nitric oxide with oxygen shown
below in kJ.
2 NO(g) + O2(g)  N2O4(g)
3.
4.
A 1.00 L flask contains a binary mixture of 1.00 g of Argon (Ar) gas and 1.00 g of CO2
gas at 25ºC. (PV = nRT; R= 0.0821 L-atm/mol.K)
(a)
What are the partial pressures of Ar and CO2 gas in torrs?
(b)
What is the total pressure of a mixture in torrs?
(c)
What is the mole fraction of CO2 gas in the mixture?
Draw all possible resonance structures (there are three) for dinitrogen monoxide (N2O)
using the atomic skeleton diagram shown below. For each Lewis structure, show the
formal charge for each atom and choose a Lewis structure that has the greatest
contribution among the resonance structures.
N ------ N -------O
5.
Using the following molecular orbital (MO) diagram given, answer the following
questions.
2p
2p
2p
2p
2p
2p
2s
2s
2s
2s
Atomic Orbitals
on C atom
Molecular
Orbitals
Atomic orbitals
on O atom
(a)
What is the bond order of CO molecule?
(B.O. = ½ (no.of bonding e- - no.of antibonding e-))
(b)
Is CO molecule paramagnetic or diamagnetic? Explain your answer.
(c )
What is the bond order of CO+ ion?
(d)
Compare the bond strength of CO molecule with that of CO+ ion and tell
which one is more stable? (hint: use the bond order argument.)