Physical Chemistry

Question 1

What is energy?

Answer 1

The capacity to do work. Total internal energy can be used to do work (w) or to transfer heat to colder surroundings (q).

Question 2

What is the first law of thermodynamics?

Answer 2

Energy cannot be created or destroyed, only transformed.

Question 3

What are the 3 key types of energy that have the most influence on a substance?

Answer 3

Kinetic, potential gravitational, and potential chemical.

Question 4

What is kinetic energy?

Answer 4

The energy a system has due to its motions, related to mass and velocity.

Question 5

What is potential gravitational energy?

Answer 5

The energy an entity has due to its relative position with respect to earth. Energy that can be used to do work when the entity changes position.

Question 6

What is potential chemical energy?

Answer 6

The energy stored in chemical bonds. Amount of energy stored in a bond and the amount of energy required to break a bond is called bond energy.

Question 7

What is ‘work’?

Answer 7

Any process that can be used to lift a weight.

Question 8

Does bond formation release or require energy?

Answer 8

Bond formation releases energy. Bond breaking requires energy.

Question 9

What is enthalpy change?

Answer 9

The change in energy occurring when a reaction takes place due to bonds broken and made.

Question 10

Define exothermic and endothermic in regards to enthalpy.

Answer 10

Exothermic - Negative enthalpy change. Energy released to surroundings.
Endothermic - Positive enthalpy change. Energy absorbed from surroundings.

Question 11

What is entropy?

Answer 11

The properties of something that gives a measure of distribution of energy in a system. The energetic disorder of a system.

Question 12

What is the relationship between entropy and the transfer of heat energy?

Answer 12

/\S=/\Q/T.

/\S = change in entropy.
/\Q = change in heat energy (J).
T - temperature in K (273K ).

Question 13

What is the second law of thermodynamics?

Answer 13

For a process to occur spontaneously, the entropy of the thermodynamic universe increases (entropy of the system decreases).

Question 14

What are the 2 key issues that influence the entropy of a reaction?

Answer 14

Temperature at which the reaction happens, and overall entropy change across the system and surroundings.

Question 15

Why does folding a polypeptide chain decrease entropy?

Answer 15

When a polypeptide chain folds, the water molecules become more disorganised and as a result the entropy of water increases.

Question 16

What is a spontaneous process?

Answer 16

One that occurs without an input of energy to keep it going once started. Happen in one direction only, reverse process is non-spontaneous (requires energy).

Question 17

What is Gibbs free energy?

Answer 17

Energy truly free to do work. /\G is the change in Gibbs free energy associated with a particular reaction.

Question 18

What units is /\G measured in?

Answer 18

Joules per mole, J mol-1.

Question 19

What does the law of conservation of energy require?

Answer 19

That the heat gained by the surroundings equals the negative of the heat lost by the system.

Question 20

If a reaction is spontaneous, is /\G positive or negative?

Answer 20

Negative. The products have lower Gibbs free energy than the reactants (exergonic).

Question 21

What is the criterion for spontaneity at the level of the universe?

Answer 21

Change in entropy must be positive (increased).

Question 22

What does the Van’t Hoff isotherm equation tell us?

Answer 22

1. A way of predicting whether a reaction will happen spontaneously if we know the equilibrium constant, K.
2. A way of estimating how far a reaction is likely to proceed if we know the value of /\G.

Question 23

How do you know if the reaction is energetically unfavourable or favourable using the Van’t Hoff isotherm?

Answer 23

If the overall term is positive (if ln K is negative) the reaction is energetically unfavourable and if it is negative, it is favourable.

Question 24

What are ionic bonds?

Answer 24

A strong electrostatic force that exist between 2 oppositely charged species, holds ions together in large 3D lattices.

Question 25

What are the 6 key types of non-covalent interactions?

Answer 25

Dispersion forces, permanent dipolar interactions, steric repulsion, hydrogen bonds, hydrophobic forces, ionic interaction.

Question 26

What are intramolecular and intermolecular interactions?

Answer 26

Intramolecular - interactions between separate parts of the same molecule.
Intermolecular - Interactions between different molecules.

Question 27

What is a dipole and what is a permanent dipole?

Answer 27

Consists of a positive charge and a negative charge separated in space within a molecule. The difference in charge between 2 ends of a dipole contributes to the dipole movement. The uneven distribution of electrons in a polar molecule is permanent so we call the molecule a permanent dipole.

Question 28

What are the 3 district types of molecular interactions that form the van Der walls interactions?

Answer 28

Dispersion forces, permanent dipolar interactions and steric repulsion.

Question 29

What are dispersion forces?

Answer 29

The force of attraction that exists between 2 areas of opposite charge (induced dipole). Temporary, weak and operate over very short distances. Larger molecules exhibit greater dispersion forces than smaller molecules because there are more electrons so more opportunities for induced dipoles.

Question 30

What is steric repulsion?

Answer 30

When 2 molecules approach each other and their electrons cause them to repel each other. Only operates over a short distance. When the molecules are further apart the attractive interactions (dispersion forces and permanent dipole-dipole) dominate to bring them together.

Question 31

What are hydrogen bonds?

Answer 31

Represents a special class of dipolar interaction. Strong interaction between a hydrogen atom of one molecule to a lone pair electronegative atom (N,O, F) on another molecule, or a distant part of the same molecule. The nuclei participating in the bond lie in a straight line and the geometry of the straight line have a big impact on the 3D structure of the compound. The strength of the bond is also influenced by the distance between the 2 electronegative atom.s

Question 32

What are examples of the importance of hydrogen bonding in biology?

Answer 32

1. Enable double-stranded DNA to adopt the helical structure by linking nucleotide bases.
2. They play an important role in folding protein structure by occurring between neighbouring amino acid side chains.
3. Determine the accuracy of translation. Strong hydrogen bonds form between complementary codons and anticodons so the remain stably associated long enough for the amino acid to be added, only weak hydrogen bonds form between uncomplimentary codons so the amino acid will not be added.

Question 33

What are ionic forces?

Answer 33

Attractive forces that exist between ionic species (species carrying full charges). The permanent ionic force that operates between 2 oppositely charged amino acid side chaos in a protein is called a salt bridge.

Question 34

What role do hydrophobic forces play in biological systems?

Answer 34

They govern the folding of a polypeptide possessing hydrophobic and hydrophilic portions to shield the hydrophobic regions from the aqueous surroundings. They also play a role in the assembly of the lipid bilayer of cell membranes.

Question 35

How do small ions mix with water in a stable way?

Answer 35

By general dipolar interactions between the charged ions and the polar water molecules through hydration. Hydration is a special form of salvation - the attraction of solvent molecules to solute ions. Hydration of ions by water molecules is essential to the functioning of biological systems.

Question 36

What are the 2 ways polar compounds can be soluble in polar solvents?

Answer 36

1. Hydrogen bonds

2. Hydration.

Question 37

How do most drugs have the ability to cross both hydrophobic and hydrophilic parts in the body to reach their target?

Answer 37

By featuring both hydrophilic and hydrophobic portions.

Question 38

What are the different levels of non-covalent bonds between the 3 groups of matter?

Answer 38

Solid - Many non-covalent interactions. Low relative energy.
Liquid - In-between
Gas - Barely any. High relative energy.

Question 39

Why do polar molecules have high melting and boiling points?

Answer 39

Because they have the highest number of non-covalent interactions so a large amount of energy is needed to break these bonds. Non-polar compounds only experience dispersion forces so they have lower MP’s and BP’s.