1. [4 marks]
An electron is excited from the ground state to the n=3 state in a hydrogen atom.
Indicate whether the following statements are true or false.
(a) It takes more energy to ionize the electron from n=3 than from the ground state.
Complete combustion of an unknown gaseous hydrocarbon yields 3.613 g of CO2 and 1.109 g of
H2O. What is the empirical formula of the unknown.
A 0.288 g sample of the same hydrocarbon as in part (a) occupies a volume of 131 mL at 24.8
Q1 [8 marks]
The following is a phase diagram for sulfur.
CIRCLE the appropriate answers to the following questions.
What is the least dense solid phase of sulfur?
Is the phase transition S(monoclinic) S(rhombic) at 1.0 atm endothermic
For each statement below, select the letter corresponding to the best answer. There is only one
correct answer per question. There are no penalties for incorrect responses.
Which atom has the largest radius?
Thermodynamic Equilibrium Constants
REMINDER: We had derived the expression for chemical
potential for a given T and P.
QUESTION: What happens when a reaction leads to a
ANSWER: We can account for this in the change of the
6.3 Calculating Entropy Changes
AIM: Show how we can account for entropy in our engineering
PROBLEM: Using the Carnot cycle, we have dened the
entropy change for the reversible case. Now we want to calculate
the entropy change due to an irrevers
EXAMPLE: (Two spin system)
Consider a system of two spins s1 = 1 and s2 = 1.
The interaction energy of the system is
E(s1, s2) = Js1 s2 ,
where J = kT .
We can write down the partition function Z of the system,
because it only has four states:
1 CHEM154 Midterm Preparation
REMINDER: The midterm will be a closed-book written exam
lasting one hour. The exam will consist of four questions
concerned with the following topics. An additional bonus question
may be answered for additional po
6.7 Gibbs Energies of Mixtures
AIM: Introduce the concept of chemical potential.
BACKGROUND: We are interested in developing a
framework for free energies when the composition of a substance
changes (chemical reactions, mixtures of particles or open
5.4 Thermochemistry: Hesss Law
BACKGROUND: Thermochemistry: study of heat during
NOTE: The First Law also applies to the enthalpy change
during chemical reactions (enthalpy of reaction).
Ignoring entropy effects:
x Exothermic reaction
Lets try to make a molecule with 2 nitrogens:
N + N GGA N N
PROBLEM: This structure does not conform to the octet rule,
its not likely to be stable.
SOLUTION: Use the four unpaired electrons to double up the
single shared bond:
N N GGA N
Transition Metal Ions
REMINDER: The outer shell electron congurations of
transition metals are of the form ns2 (n 1)110 , for example
[ Ar ]4s2 3d3 for Vanadium.
The energy levels of these s and d orbitals are nearly the same.
QUESTION: What happens when
2.10 The Periodic Table
BACKGROUND: We have learned the electronic
congurations of the elements using the Aufbau principle. The
distribution of the electrons around the nucleus determines the
chemical properties of an element.
Here, we will explore some
2.3 Potentials and Forces
AIM: Explain how to derive forces acting on particles.
A scalar eld is a scalar function that maps Cartesian space to
a scalar value : R3 R.
A scalar potential P is a scalar eld that must fulll certain
conditions (not discussed
NOTE: (Three sigma rule)
For a Normal distribution, almost all points lie within three
standard deviations from the average
( x )
2 Electrons in Atoms and Periodicity
AIM: A gentle introduction to some fundamental properties of
2.1 Measurement: SI Units
The SI (Systme Internationale dUnits) units of measurement
are widely used in Science. The base quantities dened are the
1 CHEM154 Final Exam Preparation
REMINDER: The nal will be a closed-book written exam
lasting 2.5 hours. The exam will consist of 10 questions concerned
with the following topics. An additional bonus question may be
answered for additional poin
Attractive forces between molecules Are all based on dipole-dipole interactions The larger the dipoles, the stronger the interaction
Weak forces exist between molecules called van der Waals forces. The nature o
2 Pairs: e.g. BeH2 - the molecule is LINEAR to maximize the distance between bond pairs. - H Be H bond angle is 180
H Be H
3 Pairs: e.g. BH3 - the molecule is trigonal planar - the H B H bond angle is 120
H B H
4 Electron Pairs
Textbook Problems: Chapter 6: 5, 15, 21, 23, 27 Chapter 7: 1, 3
Interactions between atoms often leads to a rearrangement of the electrons to a more stable state called bonding. The type of rearrangement lies between
The Periodic Table
Elements in the same group of the periodic table have similar electron configurations. Electrons in the outermost electron shell are called valence electrons. For example, consider Group 17 (the halogens): F Cl Br I At [He] [Ne] [Ar] [
One Electron vs. Multi Electron Atoms
In one electron atoms, all the orbitals of the same principal shell n have the same energy or are degenerate In multi electron atoms, the subshells all have different energies but the orbitals in a subshell are degen
Principal Quantum Number: n related to the size and energy of the orbital allowed values of n are positive integers > 0 n = 1,2,3,4. Orbital Angular Momentum Quantum Number: l related to the shape of the orbital allowed values are positive
The Periodic Table
The number of protons determines the element. Z = # protons (the atomic number) The number of neutrons determines the isotope A = Z + # neutrons (atomic mass number) Varying numbers of neutrons produce more than 1 isot
For O3, VSEPR predicts a trigonal planar electron-group geometry Hybridization is sp2 on central (and terminal) O atoms. Each O atom uses a sp2 + p orbital set. 18 valence electrons total, 14 in sp2 orbitals (5 lone pairs + 2 bond pairs) Three unhyb
Bonding in Acetylene (C2H2)
VSEPR predicts a linear structure Hybridization at C is sp
Describe the bonding scheme and molecular geometry of acetic acid, CH3COOH?
Molecular Orbital Theory
Molecular orbitals, like atomic orbitals, a
How do we know when to hybridize? Valence bond theory DOES NOT predict shapes of molecules It is used to account for the bonds AFTER we know the geometry We can use experiments or VSEPR to determine the expected molecular geometry