Intermolecular forces are generally much weaker than the covalent bonds that hold atoms together within a molecule.
Correct Answer
True
True. Boiling water requires about 41 kJ/mol to separate molecules from each other, while breaking the O-H bonds within water molecules takes several hundred kJ/mol. This is why phase changes leave molecules intact.
Category: Intermolecular Forces
Question 2
Hydrogen bonding occurs when a hydrogen atom bonded to carbon, nitrogen or oxygen is attracted to a lone pair on a nearby molecule.
Correct Answer
False
False. Hydrogen bonding requires hydrogen bonded to a small, highly electronegative atom: fluorine, oxygen or nitrogen. C-H bonds are not polar enough, so hydrocarbons do not hydrogen bond.
Category: Intermolecular Forces
Question 3
HF has a much higher boiling point than HCl because HF molecules hydrogen bond to one another.
Correct Answer
True
True. HF boils at about 20 degrees Celsius while HCl boils near -85 degrees Celsius, even though HCl is heavier. The strong hydrogen bonds between HF molecules outweigh the larger dispersion forces in HCl.
Category: Intermolecular Forces
Question 4
Hydrogen bonds are weaker than ordinary dipole-dipole attractions.
Correct Answer
False
False. Hydrogen bonds are an especially strong type of dipole-dipole attraction, stronger than ordinary dipole-dipole attractions. They are still much weaker than covalent bonds.
Category: Intermolecular Forces
Question 5
Surface tension arises because molecules at the surface of a liquid feel a net inward pull from the molecules below and beside them.
Correct Answer
True
True. Molecules inside a liquid are pulled equally in all directions, but surface molecules have no liquid above them, so they are pulled inward. The liquid therefore tends to minimize its surface area, which is why drops are rounded.
Category: Properties of Liquids
Question 6
Water rises higher in a wide glass tube than in a narrow one.
Correct Answer
False
False. Capillary action lifts water higher in a narrower tube, because the adhesive pull of the walls acts on a smaller column of liquid. Height of rise is inversely proportional to the tube's radius.
Category: Properties of Liquids
Question 7
Viscosity is a measure of a liquid's resistance to flow.
Correct Answer
True
True. Viscous liquids such as honey flow slowly because their molecules attract one another strongly or tangle together. Water and gasoline have low viscosity and flow easily.
Category: Properties of Liquids
Question 8
The vapor pressure of a liquid in a closed container depends on how much liquid is present.
Correct Answer
False
False. Equilibrium vapor pressure depends only on the identity of the liquid and its temperature, as long as some liquid remains. A small and a large sample of the same liquid at the same temperature have the same vapor pressure.
Category: Phase Transitions
Question 9
Water boils below 100 degrees Celsius at high altitude because the atmospheric pressure there is lower.
Correct Answer
True
True. A liquid boils when its vapor pressure equals the external pressure. With lower air pressure at altitude, water reaches that point at a lower temperature, so food cooks more slowly.
Category: Phase Transitions
Question 10
Condensation of a vapor to a liquid is an endothermic process.
Correct Answer
False
False. Condensation is exothermic: molecules release energy as attractions form between them. It is the reverse of vaporization, which absorbs energy, and the two have enthalpy changes equal in size and opposite in sign.
Category: Phase Transitions
Question 11
For water, the enthalpy of vaporization is much larger than the enthalpy of fusion.
Correct Answer
True
True. Vaporizing water takes about 40.7 kJ/mol while melting ice takes about 6.01 kJ/mol. Boiling must separate molecules almost completely, while melting only loosens their fixed arrangement.
Category: Phase Transitions
Question 12
Once a liquid in a sealed container reaches its equilibrium vapor pressure, evaporation stops.
Correct Answer
False
False. At equilibrium, evaporation and condensation continue at equal rates, so the amount of vapor stays constant. This is a dynamic equilibrium, not a halt in molecular escape.
Category: Phase Transitions
Question 13
A plot of the natural logarithm of a liquid's vapor pressure against 1/T gives a straight line whose slope is the negative of the enthalpy of vaporization divided by R.
Correct Answer
True
True. The Clausius-Clapeyron equation relates vapor pressure to temperature this way. Measuring the slope of such a plot is a common way to find a liquid's enthalpy of vaporization.
Category: Phase Transitions
Question 14
Above its critical temperature, a gas can be liquefied by applying enough pressure.
Correct Answer
False
False. Above the critical temperature, no amount of pressure can produce a separate liquid phase; the substance becomes a supercritical fluid at high pressure. A gas must be cooled below its critical temperature to be liquefied by compression.
Category: Phase Diagrams
Question 15
Each line on a phase diagram shows the temperatures and pressures at which two phases are in equilibrium.
Correct Answer
True
True. The three boundary lines separate the solid, liquid and gas regions, and along each line two phases coexist. The liquid-gas line, for example, traces the vapor pressure of the liquid at each temperature.
Category: Phase Diagrams
Question 16
Ionic solids conduct electricity well in the solid state.
Correct Answer
False
False. In an ionic solid the ions are locked in place, so it does not conduct. Ionic compounds conduct when melted or dissolved in water, because the ions are then free to move.
Category: Types of Solids
Question 17
Molecular solids such as ice and solid iodine usually have relatively low melting points.
Correct Answer
True
True. Molecular solids are held together only by intermolecular forces, which are much weaker than ionic, metallic or network covalent bonding. They are also typically soft and poor conductors.
Category: Types of Solids
Question 18
An amorphous solid such as glass has a sharp, well-defined melting point.
Correct Answer
False
False. An amorphous solid lacks a regular repeating arrangement, so its particles are held with a range of strengths and it softens gradually over a range of temperatures. Crystalline solids melt sharply at a specific temperature.
Category: Types of Solids
Question 19
In a body-centered cubic structure, each atom touches 8 nearest neighbors.
Correct Answer
True
True. The atom at the center of a body-centered cubic cell touches the 8 atoms at the corners, giving a coordination number of 8. A face-centered cubic structure has a coordination number of 12.
Category: Crystal Lattices
Question 20
A simple cubic unit cell contains a net total of 2 atoms.
Correct Answer
False
False. A simple cubic unit cell has an atom at each of its 8 corners, and each corner atom is shared by 8 cells, so the cell contains 8 x 1/8 = 1 atom. A body-centered cubic cell contains 2.
Category: Crystal Lattices