Question 1

What is the process in which molecules undergo a phase change from the gas phase to the liquid phase?

Accepted Answer

The process in which molecules undergo a phase change from the gas phase to the liquid phase is called condensation. This is where gas molecules lose energy and come together to form liquid molecules.

Question 2

What is the process in which molecules undergo a phase change from the solid phase to the liquid phase?

Accepted Answer

The process in which molecules undergo a phase change from the solid phase to the liquid phase is known as melting. This occurs when energy is added to the solid, causing the molecules to gain enough energy to break their bonds and transition into the liquid phase.

Question 3

Place the substances in order of decreasing boiling point. BeCl₂ CBr₄ BeBr₂

Accepted Answer

Boiling points generally increase with molecular weight and polarity. CBr4 has the highest molecular weight, followed by BeBr2, then BeCl2, making CBr4 > BeBr2 > BeCl2 in terms of boiling point.

Question 4

What is q if 28.6 g of water is heated from 22.0°C to 78.3°C? The specific heat of water is 4.184 J/g·°C.

Accepted Answer

To find the heat (q) absorbed or released, use the formula q = mcΔT, where m = mass of the substance, c = specific heat capacity, and ΔT = change in temperature. Here, m = 28.6 g, c = 4.184 J/g·°C, and ΔT = 78.3°C - 22.0°C = 56.3°C. So, q = 28.6 g * 4.184 J/g·°C * 56.3°C = 6737.45 J, which is approximately 6.74 kJ.

Question 5

What is the process in which molecules undergo a phase change from the liquid phase to the gas phase?

Accepted Answer

Vaporization is the process in which molecules undergo a phase change from the liquid phase to the gas phase.

Question 6

The specific heat (capacity) is

Accepted Answer

Specific heat (capacity) is the amount of energy needed to change the temperature of 1 gram of a substance by 1 degree Celsius. It is a measure of how much heat energy is required to produce a certain temperature change in a given amount of a substance.

Question 7

Which of the following properties indicates the presence of strong intermolecular forces in a liquid?

Accepted Answer

A low vapor pressure indicates strong intermolecular forces because it means that the molecules are tightly held together and therefore less likely to escape into the gas phase. Stronger intermolecular forces also lead to higher boiling points and higher heats of vaporization, so options A and D can be eliminated. The critical temperature and melting point are not directly related to intermolecular forces and can vary depending on other factors.

Question 8

Which corresponds to the temperature-dependent partial pressure above the surface of a liquid?

Accepted Answer

The vapor pressure of a liquid increases with an increase in temperature. This is the partial pressure exerted by the vapor molecules above the liquid surface. As the temperature increases, the molecules gain more kinetic energy and escape from the liquid surface more frequently, causing an increase in vapor pressure. Surface tension is a property related to the cohesive forces between the molecules at the surface of a liquid, boiling point is the temperature at which a liquid boils and turns into a gas, viscosity is the resistance of a liquid to flow, and capillary action is the ability of a liquid to flow against gravity in a narrow space.

Question 9

Which substance has the highest vapor pressure at room temperature?

Accepted Answer

HCl has the highest vapor pressure at room temperature among the options given. This is because vapor pressure is influenced by the molecular weight and intermolecular forces. HCl, being lighter and having weaker intermolecular forces compared to HF (which has strong hydrogen bonding), HBr, and HI (which are heavier), will have a higher vapor pressure.

Question 10

What is the process in which molecules undergo a phase change from the liquid phase to the solid phase?

Accepted Answer

Freezing is the process in which molecules lose energy and slow down to the point where they form a stable arrangement, resulting in a phase change from liquid to solid.

Question 11

Select the pair of substances in which the one with the lower vapor pressure at a given temperature is listed first.

Accepted Answer

The answer of Select the pair of substances in which...

Question 12

Which statement concerning the vapor pressures of water and methanol (CH₃OH) is ?

Accepted Answer

The vapor pressure of a liquid is dependent on the strength of its intermolecular forces. A liquid with weaker intermolecular forces will have a higher vapor pressure than a liquid with stronger intermolecular forces. Methanol has weaker intermolecular forces than water due to its smaller size and its polar but non-hydrogen bonding functional group (-OH instead of -H2O). Therefore, it has a higher vapor pressure than water at a given temperature.

Question 13

Place the substances in order of decreasing boiling point. CO₂ CH₄ OF₂

Accepted Answer

The substances, when decoded from the given format, are CO2, CH4, and O2. CO2 has the highest boiling point due to its molecular structure allowing for stronger intermolecular forces compared to CH4 (methane) and O2 (oxygen). O2 has a higher boiling point than CH4 because O2 is a larger molecule than CH4, leading to slightly stronger London dispersion forces.

Question 14

What is the process in which molecules undergo a phase change directly from the gas phase to the solid phase?

Accepted Answer

Deposition is the process where molecules transition directly from the gas phase to the solid phase without passing through the liquid phase.

Question 15

Which substance has the lowest vapor pressure at room temperature?

Accepted Answer

The answer of Which substance has the lowest vapor pressure...

Question 16

Place the substances in order of increasing viscosity. CH₃CH₂CH₂CH₃ H₂NCH₂CH₂NH₂ CH₃CH₂CH₂NH₂

Accepted Answer

Viscosity is the measure of a fluid's resistance to flow. The greater the viscosity, the more resistant the fluid is to flow. Based on the given substances, we can see that as the number of sulfur atoms in the molecule increases, the viscosity also increases. Therefore, CH₃ (having three sulfur atoms) will have the highest viscosity and H₂ (having no sulfur atoms) will have the least. Based on this, we can order the substances in increasing order of viscosity as: H₂ < CH₂NH₂ < CH₃CH₂CH₂CH₃. Therefore, the best choice is A.

Question 17

Select the pair of substances in which the one with the higher vapor pressure at a given temperature is listed first.

Accepted Answer

In general, the substance with the higher vapor pressure at a given temperature is the one with weaker intermolecular forces. CCl4 and CBr4 have the same number of electrons and similar molecular shapes, but the bromine atom is larger and has more polarizability, leading to weaker intermolecular forces and a higher vapor pressure. Therefore, CBr4 has a higher vapor pressure than CCl4.

Question 18

Place the substances in order of increasing boiling point. BF₃ NF₃ BeF₂

Accepted Answer

The answer of Place the substances in order of increasing...

Question 19

Place the substances in order of increasing boiling point. BeF₂ SF₂ Ar

Accepted Answer

Argon (Ar) is a noble gas with a very low boiling point due to its weak van der Waals forces. Beryllium fluoride (BeF2) and sulfur hexafluoride (SF6) are both molecular compounds, but SF6 is a larger molecule with stronger van der Waals forces than BeF2, leading to a higher boiling point. Therefore, the order from lowest to highest boiling point is Ar < BeF2 < SF6.

Question 20

What is the process in which molecules undergo a phase change directly from the solid phase to the gas phase?

Accepted Answer

The process in which molecules undergo a phase change directly from the solid phase to the gas phase is called sublimation. The other options are:

A) Deposition: The process in which molecules undergo a phase change directly from the gas phase to the solid phase.

C) Freezing: The process in which molecules undergo a phase change from the liquid phase to the solid phase.

D) Condensation: The process in which molecules undergo a phase change from the gas phase to the liquid phase.

E) Melting: The process in which molecules undergo a phase change from the solid phase to the liquid phase.

Quiz 7: Solids, Liquids, and Phase Changes