Unit 3 Practice: Easy

Answer: London dispersion forces

Explanation: All particles have moving electrons. At any moment, the electron cloud can become uneven and create a temporary dipole. This temporary dipole can induce a dipole in a nearby particle, creating London dispersion forces.

Answer: Dipole-dipole forces

Explanation: Polar molecules have permanent partial positive and partial negative regions. Opposite partial charges on nearby molecules attract each other.

Answer: N, O, or F

Explanation: Hydrogen bonding is especially strong when H is directly bonded to nitrogen, oxygen, or fluorine because these atoms are very electronegative and create strongly polarized bonds.

Answer: Ion-dipole attraction

Explanation: An ion can attract the partial charge on a polar molecule. For example, Na⁺ is attracted to the oxygen side of water molecules.

Answer: I₂

Explanation: I₂ has more electrons and a much larger electron cloud. Larger electron clouds are more polarizable, so temporary dipoles are easier to form.

Answer: Their electron clouds are more polarizable.

Explanation: Larger electron clouds are easier to distort. This creates stronger temporary dipoles and therefore stronger dispersion forces.

Answer: Higher boiling points

Explanation: More energy is required to separate molecules that attract each other strongly. Therefore, a higher temperature is needed for the liquid to boil.

Answer: Lower vapor pressure

Explanation: If molecules attract each other strongly, fewer molecules can escape the liquid phase into the gas phase. This produces a lower vapor pressure.

Answer: The pressure caused by vapor particles above a liquid at equilibrium.

Explanation: In a closed container, liquid molecules evaporate while gas molecules condense. When the rates are equal, dynamic equilibrium is established and the vapor produces a measurable pressure.

Answer: When its vapor pressure equals the external pressure.

Explanation: At that point, vapor bubbles can form throughout the liquid instead of collapsing under the external pressure.

Answer: A liquid's resistance to flow.

Explanation: Liquids with strong intermolecular attractions often flow more slowly because their molecules resist moving past one another.

Answer: The resistance of a liquid surface to being stretched or broken.

Explanation: Molecules at the surface are attracted strongly to neighboring molecules. Stronger cohesive forces can produce greater surface tension.

Answer:

PV = nRT

Explanation: The ideal gas law connects pressure, volume, amount of gas, and absolute temperature.

Answer: Kelvin

Explanation: Gas-law equations depend on absolute temperature.

Convert using:

K = °C + 273.15

Answer:

Ptotal = P1 + P2 + P3 + ...

Explanation: The total pressure of a mixture of gases equals the sum of the pressures each gas would exert on its own.

Answer: Average kinetic energy depends on Kelvin temperature.

Explanation: At the same temperature, different gases have the same average translational kinetic energy.

Answer: He

Explanation: Both gases have the same average kinetic energy, but He has much lower molar mass.

Since:

KE = 1/2 mv²

a lighter particle must move faster to have the same kinetic energy.

Answer:

M = moles of solute / liters of solution

Explanation: Molarity measures the amount of dissolved solute per liter of the total solution.

Answer:

M₁V₁ = M₂V₂

Explanation: During a simple dilution, the number of moles of solute stays constant while the solution volume increases.

Answer:

A = εbc

Explanation: Absorbance depends on:

ε = molar absorptivity

b = path length

c = concentration

Under Beer-Lambert conditions, higher concentration usually produces higher absorbance.