Calculate the percentage yield of iron in the reaction between Fe2O3 and Al, given the actual yield of Fe is 4.62 g. Also, define intermolecular forces and factors affecting hydrogen bonds.

Since aluminium is in excess, $\text{Fe}_2\text{O}_3$ is the limiting reactant. From the balanced equation, 1 mole of $\text{Fe}_2\text{O}_3$ produces 2 moles of Fe.

$$\text{Moles of Fe (theoretical)} = 0.04997 \text{ mol Fe}_2\text{O}_3 \times \frac{2 \text{ mol Fe}}{1 \text{ mol Fe}_2\text{O}_3} = 0.09994 \text{ mol Fe}$$

The molar mass of Fe is $55.845 \text{ g/mol}$.

$$\text{Mass of Fe (theoretical)} = 0.09994 \text{ mol} \times 55.845 \text{ g/mol} \approx 5.581 \text{ g}$$

The actual mass of Fe formed is $4.62 \text{ g}$.

$$\text{Percentage Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$$ $$\text{Percentage Yield} = \frac{4.62 \text{ g}}{5.581 \text{ g}} \times 100\% \approx 82.78\%$$

The percentage yield of iron is $\boxed{82.78\%}$.

Part (c): Intermolecular Forces and Hydrogen Bonds

c) (i) Intermolecular forces are attractive forces that exist between molecules. They are weaker than intramolecular forces (covalent or ionic bonds) and influence the physical properties of substances suchs as boiling point, melting point, and viscosity.

c) (ii) Two factors that influence the formation of hydrogen bonds are:

• The presence of a hydrogen atom bonded to a highly electronegative atom (N, O, or F).
• The presence of a lone pair of electrons on a highly electronegative atom (N, O, or F) in an adjacent molecule.

Part (d): Boiling Points of Water, Hydrogen Fluoride, and Methane

The boiling point of a substance is determined by the strength of the intermolecular forces between its molecules.

• Water ($\text{H}_2\text{O}$) has the highest boiling point (373 K) because its molecules form extensive hydrogen bonds. Each water molecule can form up to four hydrogen bonds, creating a strong network that requires significant energy to overcome.
• Hydrogen Fluoride (HF) has a lower boiling point (293 K) than water, but still relatively high, due to the formation of hydrogen bonds. However, each HF molecule can only form one hydrogen bond as a donor and one as an acceptor, leading to a less extensive network compared to water.
• Methane ($\text{CH}_4$) has the lowest boiling point (109 K) because it is a nonpolar molecule and only exhibits weak London dispersion forces (instantaneous dipole-induced dipole forces). These forces are much weaker than hydrogen bonds, requiring very little energy to overcome.