(Chemical and Physical Foundations) Flashcards

A fluid flows through a pipe that narrows from a cross-sectional area of 0.04 m² to 0.01 m². If the velocity in the wide section is 2 m/s, what is the velocity in the narrow section?

Answer: 8 m/s

By the continuity equation, A₁v₁ = A₂v₂: 0.04×2 = 0.01×v₂; v₂ = 8 m/s.

Which of the following statements about Le Chatelier's principle is correct when pressure is increased on the equilibrium N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?

Answer: Equilibrium shifts right to produce fewer moles of gas

Increasing pressure favors the side with fewer moles of gas; 4 moles of reactant gas form 2 moles of NH₃, so equilibrium shifts right.

Which of the following correctly describes a diamagnetic species?

Answer: It contains only paired electrons and is weakly repelled by a magnetic field

Diamagnetic species have all electrons paired; they experience weak repulsion in a magnetic field because paired electrons cancel each other's magnetic moments.

A converging lens with focal length 10 cm forms an image of an object placed 30 cm away. Where is the image located?

Answer: 15 cm on the opposite side

Using 1/f = 1/do + 1/di: 1/10 = 1/30 + 1/di; di = 15 cm on the opposite side (real image).

Which type of radioactive decay results in a product with the same mass number but a different atomic number?

Answer: Beta decay

Beta decay converts a neutron to a proton (or vice versa), changing Z by ±1 while mass number A remains constant.

At constant temperature, if the pressure of an ideal gas is tripled, the volume becomes:

Answer: One-third of the original

Boyle's Law: P₁V₁ = P₂V₂; tripling pressure reduces volume to one-third at constant temperature.

Which factor most directly determines the formal charge of an atom in a Lewis structure?

Answer: The difference between valence electrons and (lone pair electrons + half of bonding electrons)

Formal charge = valence electrons – lone pair electrons – ½(bonding electrons).