(Chemical and Physical Foundations) Flashcards

Light travels from glass (n = 1.5) into water (n = 1.33). What is the critical angle for total internal reflection?

Answer: 62.5°

sin(θc) = n₂/n₁ = 1.33/1.5 = 0.887; θc = arcsin(0.887) ≈ 62.5°.

Which of the following has the highest electron affinity?

Answer: Cl

Chlorine has the highest electron affinity among these elements because gaining one electron completes its valence shell with minimal electron-electron repulsion.

A 0.5 mol sample of an ideal gas occupies 11.2 L at STP. If the temperature is doubled at constant pressure, what is the new volume?

Answer: 22.4 L

By Charles's Law, V₁/T₁ = V₂/T₂; doubling T at constant P doubles V: 11.2 × 2 = 22.4 L.

In a second-order reaction, when the initial concentration of reactant is doubled, what happens to the half-life?

Answer: It is halved

For a second-order reaction, t½ = 1/(k[A]₀); doubling [A]₀ halves the half-life.

Which property of sound waves increases when the medium's temperature rises?

Answer: Speed

Sound speed in a gas increases with temperature because molecules move faster, transmitting vibrations more quickly.

An atom has the electron configuration [Ar] 3d⁵ 4s¹. Which element is this?

Answer: Chromium (Cr)

Chromium (Z=24) has the anomalous configuration [Ar] 3d⁵ 4s¹ due to the extra stability of a half-filled d subshell.

A solution is prepared by dissolving 0.1 mol NaCl in 1 kg of water. What is the expected freezing point? (Kf water = 1.86°C/m)

Answer: –0.372°C

NaCl dissociates into 2 ions, so i = 2; ΔTf = iKfm = 2 × 1.86 × 0.1 = 0.372°C depression.