Introduction & Fundamentals

Question 1

Why is chemistry important in understanding climate change?

Answer 1

It helps in understanding the reason chemical pollutants can endanger the
environment and greenhouse gases cause the warming of our planet.

It helps in understanding the energy balance (i.e. the radiative forcing and its
heating and cooling effects) and the behavior (especially persistency) of
chemicals in the environment.

It helps to better understand the effective policy to be undertaken in order to
mitigate climate change.

Most importantly, it helps to understand the interaction of humans with
invisibles.

Question 2

What is the periodic table?

Answer 2

The arrangement of the elements in order of increasing atomic number, with
elements having similar properties placed in a vertical column, is called the
PERIODIC TABLE.

Columns are called GROUPS (FAMILIES) and rows are called PERIODS. Elements in the same group have similar chemical and physical properties. Physical and chemical properties such as melting points, thermal and electrical conductivity, atomic size, vary systematically across the Periodic Table.

Question 3

What is matter made of?

Answer 3

Matter is made up of atoms. The structure of atoms dictates their properties. How atoms combine dictate what we see in the matter (e.g. minerals) in nature. Matter comes in three states:

Solid: defined shape and definite volume
Liquid: undefined shape and definite volume
Gas: undefined shape and undefined volume (can be compressed and expanded)

Question 4

Atoms and elements

Answer 4

Elements: about a hundred fundamental kinds of matter. Each element identifies chemically identical atoms.

Each atom is made by subatomic particles:
•Positively charged protons in the atom’s nucleus.
•Uncharged neutrons in nucleus.
•Negatively charged electrons in a cloud around nucleus

Question 5

What is the atomic number?

Answer 5

Elements are designated by atomic number which is equal to the number of
protons in the nucleus, and the number of electrons around it, of each atom.

Question 6

What is the Chemical Symbol?

Answer 6

Each element is designated by a chemical symbol, such as O for oxygen.

Question 7

What is the atomic mass?

Answer 7

Each element has an atomic mass, which is the average mass of all atoms of
an element in atomic mass units, u, also called daltons.

Question 8

What are isotopes?

Answer 8

Atoms of the same element containing equal numbers of protons but different
numbers of neutrons in their nuclei are called isotopes. They differ in relative
atomic mass but not in chemical properties.

Some isotopes are radioactive and undergo radioactive decay in which their
nuclei are transformed to nuclei of other elements

Question 9

What is the mole?

Answer 9

Mole, also spelled mol, in chemistry, a standard scientific unit for measuring large quantities of very small entities such as atoms, molecules, or other specified particles –> the mole has been defined as the amount of substance of a system
which contains as many elementary entities as there are atoms in 12 g of 12C.

1 mol = 6.023 · 10^23 entities -> Number of Avogadro

Since atomic mass units (amu) are defined as one twelfth of the mass one atom of 12C (1 amu = 1.66 · 10-24 g) it can be seen that:

6.023 · 10^23 amu = 1.00 g

Thus, the weight of 1 mol of a chemical substance is equal to the sum of the
atomic weights of its atoms.

Question 10

What is the electronic configuration?

Answer 10

The arrangement of electrons in the space around the nucleus of an atom is
called “electronic configuration”.

The first model to describe the movement of electrons around an atom
nucleus was introduced by Niels Bohr, who said that the electron is able to
revolve around the nucleus without radiating any energy only at certain
discrete distances from the nucleus.

The model suggested by Bohr did not account for the dual particle-wave
nature of electrons.

Erwin Schrödinger proposed a mathematic equation (i.e. Schrödinger’s
equation) to describe probability of finding the position of an electron
around the atom nucleus.

In particular, the regions where there is a probability of finding an electron
higher than 95% are called orbitals.

Question 11

What are intramolecular bonds?

Answer 11

Intramolecular forces hold atoms together in a molecule:

• Ionic bond: large differences in electronegativity between two bonded atoms favor the transfer of electrons from the less electronegative (more electropositive) atom to the more electronegative atom
• Covalent bond: smaller differences of electronegativity result in a more equitable
  “sharing” of electrons between the bonded atoms.

Question 12

What are intermolecular bonds?

Answer 12

Intermolecular forces are attractive forces between molecules:

• Hydrogen bond (strongest): dipole-dipole interaction between the hydrogen
  atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom.

Question 13

Types of intermolecular forces

Answer 13

• Ion-dipole interaction: Attractive forces between an ion and a polar molecule.
• Dipole-dipole interactions: Attractive forces between polar molecules.

• Dispersion forces/van der Walls forces/London forces (weakest): Attractive
forces that arise as a result of temporary dipoles induced in atoms or molecules.

Question 14

What is the molecular shape?

Answer 14

• The shape of a molecule is determined by repulsions between all the electrons present in the valence shell.

• Electron pairs in the valence shell of the central atom repel each other and align
themselves to minimize this repulsion.

Question 15

What are the properties of ionic compounds?

Answer 15

Ionic compounds are made of ionic bonds where the atoms are electrostatically attracted towards each other. Ionic compounds occur through the interaction between cations and anions.

Question 16

What are molecular compounds?

Answer 16

Molecular compounds are not good electrical conductors. Covalent bonds are quite weak, hence most compounds exist in the gaseous phase.

Question 17

What are the types of interactions with water?

Answer 17

• Hydrophilic: substance that is attracted to water molecules and tends to be
  dissolved by water (e.g. salts, alcohols) .

- Hydrophobic: substance that is repelled by water and tends to be immiscible
in water (e.g. oil, petroleum)

• Amphipathic: substance having both hydrophilic and hydrophobic parts (e.g.
  soap)

Question 18

What is a phase change?

Answer 18

A “phase transition”, or “phase change”, is defined as a change from one
state of matter (solid, liquid, gas) to another.

Question 19

Density of water

Answer 19

Water is a unique substance: it has maximum density at 4 °C.
Ice is less dense than water and floats, while cold water (at 4°C) sinks to the
bottom: the temperature of the water under the ice is maintained at 4°C even
when the temperature of the air is well below 0°C.

Question 20

What is the triple point?

Answer 20

Triple point: the point on a phase diagram at which the three states of matter: gas, liquid, and solid coexist.

Question 21

What is the critical point?

Answer 21

Critical point: the point on a phase diagram at which the substance is indistinguishable between liquid and gaseous states.

Question 22

What is a phase diagram?

Answer 22

A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas.

Question 23

What is a fusion curve?

Answer 23

Fusion(melting) (or freezing) curve – the curve on a phase diagram which represents the transition between liquid and solid states.

Question 24

What is a vaporization curve?

Answer 24

Vaporization (or condensation) curve – the curve on a phase diagram which
represents the transition between gaseous and liquid states.

Question 25

What is a sublimation curve?

Answer 25

Sublimation (or deposition) curve – the curve on a phase diagram which
represents the transition between gaseous and solid states.

Question 26

What is thermodynamics?

Answer 26

Thermodynamics is the study of energy changes accompanying physical
and chemical changes. The term itself clearly suggests what is happening –
“thermo”, from temperature, meaning energy, and “dynamics”, which
means the change over time.

Question 27

What is a system?

Answer 27

System: anything that is kept into consideration.

Systems can be

• Isolated: no exchange of matter nor heat.
• Closed: no exchange of matter but some exchange of heat
• Open: exchange of both matter and heat

Related to the system:

• Surroundings: everything external to the system
• Boundary: the separation between the system and the surroundings
• Universe: the sum of system(s) and surroundings

Question 28

What are intensive and extensive properties?

Answer 28

Intensive properties do not depend on the amount of matter in a sample: temperature, boiling point, concentration, luster.

Extensive properties depend on how much matter a sample contains: weight, length, volume, entropy.

Question 29

Zeroth Law of Thermodynamics

Answer 29

It is the reason why thermometers work.
It states that when two objects are separately in thermodynamic equilibrium with a third object, they are in equilibrium with each other. This allows the assignment of a
unique temperature to systems with are in thermal equilibrium with each other.

Question 30

First law of thermodynamics

Answer 30

The first law of thermodynamics is an extension of the law of conservation of
energy (energy can be changed, moved, controlled, stored, or dissipated, but
it cannot be created from nothing or reduced to nothing).

It states that: The change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

Question 31

Second law of thermodynamics

Answer 31

The second law of thermodynamics states that a natural process that starts
in one equilibrium state and ends in another will go in the direction that causes the entropy (S) of the system plus the surroundings (i.e. of the universe) to increase for an irreversible process and to remain constant for a reversible process.

Question 32

What is a spontaneous process?

Answer 32

Spontaneous processes are those that can proceed without any outside intervention. Processes that are spontaneous in one direction, are non-spontaneous in the reverse direction. Processes that are spontaneous at one temperature may be non-spontaneous at other temperatures. For example, above 0°C it is spontaneous for ice to melt, but below 0°C the reverse process is spontaneous.

Question 33

What is entropy?

Answer 33

Entropy, the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work. Because work is obtained from ordered molecular motion, the amount of entropy is also a measure of the molecular disorder, or randomness, of a system.

Question 34

Entropy at the molecular scale

Answer 34

Since temperature is a measure of the average kinetic energy of the molecules in a sample, it can be related to the concept of entropy on the molecular level.

• Ludwig Boltzmann envisioned the motions of a sample of molecules at a
  particular instant in time, like taking a snapshot of all the molecules.
• He referred to this sampling as a micro-state of the thermodynamic system.

Each thermodynamic state has a specific number of micro-states (W), associated with it. Entropy is –> S= k log W. (where k is the Boltzmann constant).

Boltzmann equation has several implications:
• More particles → more states → more entropy
• Higher T → more energy states → more entropy
• Less structure (gas vs solid) → more states → more entropy

Question 35

When does entropy increase?

Answer 35

When Gases are formed from liquids and solids.
When Liquids or solutions are formed from solids.
When the number of gas molecules increases.
When the number of moles increases.

Question 36

Third law of thermodynamics

Answer 36

The third law of thermodynamics states, regarding the properties of closed systems in thermodynamic equilibrium: the entropy of a system approaches a constant value when its temperature approaches absolute zero.

The third law of thermodynamics leads to the definition of “absolute zero”,
the temperature where atoms and molecules do not move. Since it is impossible to completely isolate a system, it also states that absolute zero can not be reached.

Question 37

Different meanings of “equilibrium”

Answer 37

The word “equilibrium” has several different meaning, depending on the
discipline considered:

• Physical equilibrium: For an object or system to be in equilibrium, the sum
of the forces acting on it must be zero.
• Economical equilibrium: Equilibrium is the state in which market supply
and demand balance each other, and as a result prices become stable.
• Chemical equilibrium: For a chemical reaction to be at equilibrium, the rate
of the forward reaction must be equal to the rate of the backward reaction. In other words, once equilibrium is achieved, there is no net change in concentrations of reactants and products (i.e. the amount of each substance remains constant).

Question 38

The equilibrium constant

Answer 38

In a system at equilibrium, both the forward and reverse reactions are being
carried out and their rates (k) are constant, therefore an equilibrium constant
Keq can be defined:

Keq = kforward
kreverse

Keq depends on:
• Nature of reactants and products;
• Temperature (at constant volume and pressure)

If Keq&raquo_space; 1 : the reaction is product-favored; product predominates at equilibrium.
If Keq &laquo_space;1 : the reaction is reactant-favored; reactant predominates atequilibrium.

Question 39

Dissociation of water

Answer 39

One of the fundamental equilibrium reactions in chemistry is the dissociation
of water:

Keq = [H+][OH-] = 10^-14
[H2O]

pH is defined as –log10([H+]), and since forwater dissociation Keq= 10^-14, it can vary between 0 and 14.

Question 40

Rate limiting step

Answer 40

Equilibrium thermodynamics predicts the final state of a system.
Kinetics tells you if it will get there in a reasonable amount of time.

There are factors that must occur for a reaction to take place, such as:

• breaking bonds and crystal structure.
• diffusion and micro-environments in solutions.
• multi-step reactions disguised as one step (e.g. phase transition between involving intermediate minerals).

Of all the intermediate factors, the slowest one, determines the rate of the
overall reaction (RATE LIMITING STEP).

Question 41

Presence of catalysts

Answer 41

Catalysts increase the rate of both the forward and reverse reactions.
In the presence of a catalyst equilibrium is achieved faster, but the equilibrium composition remains unaltered.

Some examples of catalysts include:
➢ Enzymes
➢ H+/OH-
➢ Heavy metals and metalloids
➢ Organic chemicals

Question 42

LE CHÂTELIER’S PRINCIPLE

Answer 42

“If a system at equilibrium is disturbed by a change in temperature, pressure,
or the concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance.”

Question 43

Endothermic and exothermic reactions

Answer 43

The equilibrium constant is temperature dependent.

• If a reaction requires heat, it is called endothermic (i.e. heat can be considered as a reactant).
• If a reaction produces heat, it is called exothermic (i.e. heat can be considered as a product).
• Adding heat (i.e. heating the vessel) favors away from the increase of temperature:

o if endothermic: adding heat favors the forward reaction.
o if exothermic: adding heat favors the reverse reaction.

Question 44

What is concentration?

Answer 44

In chemistry, concentration is usually defined as the relative amount of a particular substance contained within a solution or mixture or in a particular volume of space.

It can be expressed in several ways:
➢ Number of entities per unit of volume: Molarity (mol/L, i.e. moles of solute / litres of solution)
➢ Number of entities per unit of mass: Molality (mol/kg, i.e. moles of solute / kg of solvent)