Phase Diagrams & States of Matter practice questions

Question 1

A student analyzes a pure solid substance composed of two elements with an electronegativity difference of $2.1$. Which of the following correctly identifies the predominant type of bonding in the substance and its electrical conductivity?

Accepted Answer

Ionic | Conducts when molten

Answer

Covalent | Conducts in the solid state

Answer

Covalent | Conducts when molten

Answer

Ionic | Conducts in the solid state

Question 2

A student observes the particulate representations below, representing a pure substance $X$ undergoing a physical change in a sealed, rigid container of constant volume. Which of the following correctly compares the particle density and translational mobility of substance $X$ in Box $2$ relative to Box $1$?

Accepted Answer

In Box $2$, the particle density is lower and the translational mobility of the particles is greater than in Box $1$.

Answer

In Box $2$, the particle density is higher and the translational mobility of the particles is greater than in Box $1$.

Answer

In Box $2$, the particle density is lower and the translational mobility of the particles is smaller than in Box $1$.

Answer

In Box $2$, the particle density is higher and the translational mobility of the particles is smaller than in Box $1$.

Question 3

A student subjects a crystal of sodium chloride, $\text{NaCl(s)}$, to a mechanical shearing force, causing the crystal to cleave cleanly along a plane as represented in the diagram below. Which of the following claims best explains why ionic solids such as $\text{NaCl(s)}$ are brittle and fracture when a stress is applied?

Accepted Answer

The crystal fractures because the applied force shifts layers of ions, aligning ions of like charge adjacent to one another and producing strong electrostatic repulsions.

Answer

The crystal fractures because the applied force disrupts a sea of delocalized valence electrons, preventing them from cushioning the movement of cations.

Answer

The crystal fractures because directional covalent bonds between the sodium and chlorine atoms are rigid and cannot bend under mechanical pressure.

Answer

The crystal fractures because the applied force pushes oppositely charged ions closer together, increasing attractive forces until the lattice collapses.

Question 4

A laboratory inventory includes three solid materials: silicon carbide ($\text{SiC}$), potassium bromide ($\text{KBr}$), and brass (an alloy of $\text{Cu}$ and $\text{Zn}$). Which of the following options correctly identifies the primary type of bonding present in each material?

Accepted Answer

$\text{SiC}$: Network covalent; $\text{KBr}$: Ionic; Brass: Metallic

Answer

$\text{SiC}$: Molecular covalent; $\text{KBr}$: Ionic; Brass: Metallic

Answer

$\text{SiC}$: Network covalent; $\text{KBr}$: Metallic; Brass: Ionic

Answer

$\text{SiC}$: Ionic; $\text{KBr}$: Network covalent; Brass: Metallic

Question 5

A student passes steam through a metal coil immersed in a cooler water bath. Inside the coil, the steam changes from $\text{H}_2\text{O(g)}$ at $100^\circ\text{C}$ to $\text{H}_2\text{O(l)}$ at $100^\circ\text{C}$, and the temperature of the water bath increases.

Which statement correctly classifies the condensation and explains the associated energy transfer?

Accepted Answer

The condensation is exothermic because stronger intermolecular attractions lower the potential energy of the $\text{H}_2\text{O}$ molecules, transferring energy to the surroundings.

Answer

The condensation is exothermic because the average kinetic energy of the $\text{H}_2\text{O}$ molecules decreases during the phase change.

Answer

The condensation is endothermic because the $\text{H}_2\text{O}$ molecules must absorb energy to overcome intermolecular attractions as they enter the liquid phase.

Answer

The condensation is endothermic because stronger intermolecular attractions lower the potential energy of the $\text{H}_2\text{O}$ molecules, transferring energy to the surroundings.

Question 6

A student compares the physical properties of silicon dioxide, $\text{SiO}_2\text{(s)}$, and carbon dioxide, $\text{CO}_2\text{(s)}$. The student notes that $\text{SiO}_2\text{(s)}$ has a melting point of $1710^\circ\text{C}$, whereas $\text{CO}_2\text{(s)}$ sublimes at $-78^\circ\text{C}$ at atmospheric pressure. Which of the following statements best accounts for the large difference in phase-change temperatures between the two substances?

Accepted Answer

$\text{SiO}_2\text{(s)}$ has a much higher melting point because phase change requires breaking strong covalent bonds within a continuous network lattice, whereas phase change of $\text{CO}_2\text{(s)}$ requires overcoming much weaker intermolecular forces between discrete molecules.

Answer

$\text{SiO}_2\text{(s)}$ has a much higher melting point because melting $\text{SiO}_2\text{(s)}$ breaks the strong $\text{Si}-\text{O}$ covalent bonds within discrete $\text{SiO}_2$ molecules, whereas melting $\text{CO}_2\text{(s)}$ breaks the weaker $\text{C}=\text{O}$ double bonds within discrete $\text{CO}_2$ molecules.

Answer

$\text{CO}_2\text{(s)}$ has a much lower sublimation temperature because the polar $\text{C}=\text{O}$ bonds create repulsive forces between adjacent $\text{CO}_2$ molecules, whereas nonpolar $\text{Si}-\text{O}$ bonds in $\text{SiO}_2$ attract each other.

Answer

$\text{CO}_2\text{(s)}$ has a much lower sublimation temperature because phase change requires breaking covalent bonds in $\text{CO}_2\text{(s)}$, whereas phase change of $\text{SiO}_2\text{(s)}$ requires overcoming only London dispersion forces.

Question 7

A student investigates the thermal properties of three solid metal samples: $\text{Al(s)}$, $\text{Fe(s)}$, and $\text{Ag(s)}$. Each sample has a mass of $10.0 \text{ g}$ and an initial temperature of $25.0^\circ\text{C}$. The student transfers $180 \text{ J}$ of heat to each sample. The specific heat capacities of the three metals are given in the table below.

| Metal | Specific heat capacity ($\text{J/(g}\cdot^\circ\text{C)}$) |
|---|---|
| $\text{Al(s)}$ | $0.90$ |
| $\text{Fe(s)}$ | $0.45$ |
| $\text{Ag(s)}$ | $0.24$ |

Which of the following correctly ranks the metals in order of the magnitude of their temperature change ($\Delta T$), from greatest to least?

Accepted Answer

$\text{Ag(s)} > \text{Fe(s)} > \text{Al(s)}$

Answer

$\text{Al(s)} > \text{Fe(s)} > \text{Ag(s)}$

Answer

$\text{Al(s)} > \text{Ag(s)} > \text{Fe(s)}$

Answer

$\text{Ag(s)} > \text{Al(s)} > \text{Fe(s)}$

Question 8

A student conducts an experiment to compare the thermal energy required for phase changes of water, $\text{H}_2\text{O}$. The student measures the thermal energy required to completely melt a $18.0 \text{ g}$ sample of ice at $0^\circ\text{C}$ ($q_{\text{fus}}$) and the thermal energy required to completely vaporize a $18.0 \text{ g}$ sample of liquid water at $100^\circ\text{C}$ ($q_{\text{vap}}$). Which of the following correctly compares $q_{\text{vap}}$ to $q_{\text{fus}}$ and provides the correct molecular explanation?

Accepted Answer

$q_{\text{vap}} > q_{\text{fus}}$, because vaporization requires completely overcoming all intermolecular hydrogen bonds, whereas fusion requires only partially disrupting the hydrogen bonding network.

Answer

$q_{\text{vap}} < q_{\text{fus}}$, because ice has a lower density than liquid water, requiring more energy to expand the crystal structure during melting.

Answer

$q_{\text{vap}} < q_{\text{fus}}$, because melting requires breaking covalent $\text{O-H}$ bonds within $\text{H}_2\text{O}$ molecules, whereas boiling only disrupts intermolecular hydrogen bonds.

Answer

$q_{\text{vap}} > q_{\text{fus}}$, because vaporization requires breaking intramolecular covalent $\text{O-H}$ bonds, whereas fusion requires only overcoming intermolecular hydrogen bonds.

Question 9

A student applies a sharp mechanical force to a crystal of sodium chloride, $\text{NaCl(s)}$. The particulate representation below shows the arrangement of ions in a section of the crystal lattice before and after the force causes the top layers of ions to shift relative to the bottom layers. Based on the representation, which of the following best explains why the ionic crystal cleaves along the plane of force rather than deforming malleably?

Accepted Answer

The applied force shifts the layers so that ions of like charge align, creating strong repulsive electrostatic forces that cause the crystal to cleave.

Answer

The applied force causes like-charged ions to align, producing attractive electrostatic forces that hold the shifted layers together.

Answer

The applied force breaks nonpolar covalent bonds between adjacent ions, causing the crystal lattice to fracture.

Answer

The applied force causes valence electrons to become delocalized, reducing electrostatic attraction and allowing layers to slide past one another.

Question 10

A student compares the scratch hardness and cleavage behavior of three crystalline solids. Cleavage is observed when a sharp blow causes a solid to split along flat, repeating surfaces.

| Solid | Approximate Mohs hardness | Observation after a sharp blow | Structural description |
|---|---:|---|---|
| Diamond, $\text{C(s)}$ | 10 | Flat surfaces form along certain orientations | Each $\text{C}$ atom is covalently bonded to four other $\text{C}$ atoms in a three-dimensional network. |
| Quartz, $\text{SiO}_2\text{(s)}$ | 7 | Irregular surfaces form without cleavage | Covalent $\text{Si}-\text{O}$ bonds extend throughout a three-dimensional framework without distinct layers. |
| Graphite, $\text{C(s)}$ | 1–2 | Thin, flat sheets separate readily | Strong covalent bonds connect $\text{C}$ atoms within each sheet, and London dispersion forces act between sheets. |

Which of the following best explains the hardness and cleavage results?

Accepted Answer

Hardness and cleavage test different responses: diamond's strong three-dimensional network resists scratching but can split along planes where fewer bonds oppose separation; quartz lacks layered weak regions, and graphite separates between sheets held by dispersion forces.

Answer

Diamond's high hardness means that its cleavage cannot involve breaking covalent bonds; therefore, diamond must contain unrepresented molecular layers held together by weak intermolecular forces.

Answer

Quartz's lack of cleavage means that quartz should be harder than diamond, because a solid that fractures irregularly always requires more energy to scratch than one that cleaves.

Answer

Graphite is soft and cleaves readily because the $\text{C}-\text{C}$ covalent bonds within each sheet are much weaker than those in diamond, so both tests separate atoms within a sheet.

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