Higher Chemistry Review: Bonding, Periodicity, Rates, and Organic Chemistry

Comprehensive practice flashcards covering Bonding and Structure, Rates of Reactions, Periodicity, Esters, Fats, Oils, Soaps, Proteins, Fragrances, Skincare, and Oxidation of Alcohols.

Which type of bonding and structure is found in elemental phosphorus?

Covalent molecular,

In terms of structure and intermolecular forces, why is the boiling point of chlorine much higher than that of argon?

Chlorine exists as diatomic molecules ($Cl_2$) with $34$ electrons per molecule, whereas argon exists as monatomic atoms ($Ar$) with $18$ electrons. Both experience London dispersion forces, but the larger number of electrons in chlorine results in stronger London dispersion forces requiring more energy to separate.

What dipole notation and relative position of bonding electrons represents the polar covalent bond in hydrogen chloride?

A

Why is caesium fluoride identified as having greater ionic character than sodium fluoride, caesium iodide, or sodium iodide?

Caesium has the lowest electronegativity and fluorine has the highest electronegativity, creating the greatest difference in electronegativity between the bonded atoms.

Why is silicon dioxide much higher melting ($1610\,^\circ\text{C}$) than sulfur ($113\,^\circ\text{C}$)?

Melting silicon dioxide requires breaking strong covalent bonds in a covalent network lattice, whereas melting sulfur only requires overcoming weak London dispersion forces between discrete $S_8$ molecules.

Why is polar covalent bonding never found in elements?

Bonds between atoms of the same element have an electronegativity difference of zero, meaning the bonding electrons are shared equally in a non-polar covalent bond.

Based on the potential energy diagram shown, what is the enthalpy change ($\Delta H$), in $kJ$, for the forward reaction between hydrogen and iodine?

$$\Delta H = E_{a\text{ (forward)}} - E_{a\text{ (backward)}} = 173.2\,kJ - 182.8\,kJ = -9.6\,kJ$$

In reaction kinetics, what term describes the high-energy, unstable arrangement of atoms formed at the top of the potential energy barrier?

The activated complex.

According to collision theory, what two requirements must be satisfied for collisions to result in product formation?

Reactant particles must collide with kinetic energy equal to or greater than the activation energy ($E \ge E_a$) and must collide with the correct collision geometry.

Why does a relatively small increase in temperature lead to a large increase in the rate of a chemical reaction?

Increasing temperature increases the average kinetic energy of the molecules, significantly increasing the proportion of molecules that have energy equal to or greater than the activation energy ($E \ge E_a$).

For any chemical substance, what physical quantity does temperature directly measure?

The average kinetic energy of all the particles in the substance.

How does the addition of a catalyst affect the activation energy and reaction rate?

A catalyst provides an alternative reaction pathway with a lower activation energy, increasing the number of successful collisions per second without changing the enthalpy change ($\Delta H$).

Which element in the third period of the Periodic Table possesses a covalent network structure?

Silicon ($Si$).

What is the equation, including state symbols, representing the second ionisation energy of magnesium?

$$Mg^+(g) \rightarrow Mg^{2+}(g) + e^-$$

Why is there a large difference between the third ($2745\,kJ\,mol^{-1}$) and fourth ($11577\,kJ\,mol^{-1}$) ionisation energies of aluminium?

The fourth electron must be removed from a full, stable inner electron shell closer to the nucleus, which experiences a much stronger nuclear attraction.

Why does the covalent radius decrease across a period from left to right (e.g., from sodium to chlorine)?

The nuclear charge increases (more protons are present in the nucleus) while electrons are added to the same outer energy level, pulling the outer electrons closer to the nucleus.

Why is no electronegativity value provided for the noble gas argon?

Argon has a stable, full outer shell of electrons and does not form covalent bonds with other elements.

Why do boiling points of the halogens increase down Group 7 from fluorine to iodine?

The size of the molecules and number of electrons increase down the group, resulting in stronger London dispersion forces that require more thermal energy to overcome.

What products are obtained from the alkaline hydrolysis of pentyl butanoate using sodium hydroxide?

Pentan-1-ol and sodium butanoate (the sodium salt of butanoic acid).

In detergent and soap chemistry, what term describes the non-polar, hydrocarbon tail of the molecule?

Hydrophobic.

What chemical process is carried out to convert liquid vegetable oils into solid hardened fats for margarines?

Hydrogenation (the addition of hydrogen across carbon-carbon double bonds).

Why do edible vegetable oils have lower melting points than animal fats?

Vegetable oils have a higher degree of unsaturation (more carbon-carbon double bonds), creating kinked chains that prevent close packing, which weakens the London dispersion forces between molecules.

In an ester preparation experiment, why is a wet paper towel wrapped around the test tube?

It acts as a condenser, cooling and condensing volatile reactant and product vapours so they drip back into the mixture rather than escaping.

What small, water-soluble molecules are formed when proteins are completely broken down by hydrolysis?

Amino acids.

What term describes the change in shape of a protein or enzyme molecule caused by altered temperature or pH?

Denaturation (the protein becomes denatured).

What term is used to describe amino acids that cannot be synthesized by the human body and must be supplied by the diet?

Essential amino acids.

How does an amino acid such as serine or glycine form a zwitterion in aqueous solution?

A hydrogen ion ($H^+$) is transferred from the acidic carboxyl group ($-COOH$) to the basic amino group ($-NH_2$), forming a $-COO^-$ and an $-NH_3^+$ group on the same molecule.

What are the three stages of a free radical chain reaction?

Initiation, propagation, and termination.

What is the definition of a free radical?

An atom or molecular fragment that contains an unpaired electron, making it highly reactive.

How many isoprene units are used in the production of one limonene molecule?

$2$ isoprene units (limonene contains $10$ carbon atoms; each isoprene unit contains $5$ carbon atoms).

Why are non-polar flavour compounds better retained in food when the food is cooked in water?

Non-polar flavour compounds are insoluble in polar water, so they do not dissolve into the cooking water and remain in the food.

What is the systematic IUPAC name for the compound shown?

2,2-dimethylpropan-1-ol

Why cannot tertiary alcohols be easily oxidised by oxidising agents like acidified potassium dichromate?

The carbon atom bonded to the hydroxyl group ($-OH$) is directly bonded to three other carbons and has no hydrogen atom attached to it.

What colour change is observed when an aldehyde is warmed with Fehling's or Benedict's solution?

The blue solution turns into a brick-red precipitate.

Why is the boiling point of ethane-1,2-diol ($197\,^\circ\text{C}$) much higher than that of propan-1-ol ($98\,^\circ\text{C}$) despite their similar molecular masses?

Ethane-1,2-diol contains two hydroxyl ($-OH$) groups per molecule compared to one in propan-1-ol, enabling more extensive hydrogen bonding between molecules.