(Chemical and Physical Foundations) Flashcards

Which of the following correctly ranks carbon-carbon bond lengths from shortest to longest?

Answer: C≡C < C=C < C–C

Triple bonds are shorter than double bonds, which are shorter than single bonds due to increased electron density pulling nuclei closer.

A projectile is launched horizontally from a cliff 80 m high at 20 m/s. How far from the base of the cliff does it land? (g = 10 m/s²)

Answer: 80 m

Time to fall: h = ½gt² → t = √(2×80/10) = 4 s; horizontal distance = 20 × 4 = 80 m.

Which intermolecular force is responsible for the unusually high surface tension of water?

Answer: Hydrogen bonding

Water's extensive hydrogen bonding network creates strong cohesive forces between molecules, resulting in high surface tension.

A reaction has ΔH = –50 kJ/mol and ΔS = –100 J/(mol·K). At what temperature does this reaction become non-spontaneous?

Answer: Above 500 K

ΔG = ΔH – TΔS; spontaneous when ΔG ΔH/ΔS = 50,000/100 = 500 K.

Which of the following best explains why the pH of a strong acid solution with concentration 1×10⁻⁸ M is NOT 8?

Answer: The autoionization of water contributes significantly to [H⁺] at very low acid concentrations

At 10⁻⁸ M, the H⁺ from water autoionization (10⁻⁷ M) dominates, so the actual [H⁺] ≈ 10⁻⁷ M and pH ≈ 7, not 8.

Two point charges of +2 μC and +8 μC are 12 cm apart. At what distance from the +2 μC charge does the electric field equal zero?

Answer: 4 cm

Setting kQ₁/r² = kQ₂/(d–r)²: 2/r² = 8/(12–r)²; solving gives r = 4 cm from the +2 μC charge.

Which statement about enzyme kinetics is correct when substrate concentration is well above Km?

Answer: Both B and C are correct

When [S] >> Km, the enzyme is saturated and operates at Vmax; since rate is constant regardless of [S], this is zero-order kinetics—so both B and C describe the same phenomenon.