Mastering Chemistry Week 5 Sections: 11.5-11.12

Open the phase diagram for CO2 given in the introduction again. Use the phase diagram for CO2 in the interactive activity and determine which of the following statements are correct. Check all that apply.

*When the pressure is 1 atm, there is no temperature at which the liquid phase of CO2 exists. *All three phases of CO2 exist simultaneously at the triple point. *Movement across boundary line BO corresponds to a phase change. *CO2 is a gas under normal conditions of temperature and pressure. When the pressure is 4 atm and the temperature is more than −56.7∘C, CO2 exists as a solid. CO2 forms a supercritical fluid at temperatures less than 31∘C.

Polonium

1 atom/unitcell

Give the coordination number for a body-centered cubic cell.

12 10 6 0 *8

Tungsten

2 atom/unitcell

Nickel

4 atom/unitcell

A mixture containing 21.4 g of ice (at exactly 0.00 ∘C) and 75.3 g of water (at 70.0 ∘C) is placed in an insulated container. Assuming no loss of heat to the surroundings, what is the final temperature of the mixture?

41.9 ∘C 32.6 ∘C 38.2 ∘C *36.8 ∘C

Calculate the amount of heat required to completely sublime 67.0 g of solid dry ice (CO2) at its sublimation temperature. The heat of sublimation for carbon dioxide is 32.3 kJ/mol.

49.2 kJ

Calculate the amount of heat (in kJ) required to vaporize 2.51 kg of water at its boiling point. ( ΔHvap=40.7 kJ/mol at 100 ∘C)

5670 kJ

Tungsten has a body-centered cubic unit cell. How many atoms of W are present in each unit cell? Express your answer as an integer.

8/8+1= 2

Nickel has a face-centered cubic unit cell. How many atoms of Ni are present in each unit cell? Express your answer as an integer.

8/8+6/2= 4

Mercury is a poisonous metal that is used in thermometers. When mercury is at temperatures below its freezing point it has a simple cubic unit cell. How many atoms of Hg are present in each unit cell? Express your answer as an integer.

8/8= 1

Classify the following phase changes as exothermic processes or endothermic processes.

Exothermic Process: freezing, condensing, deposition Endothermic Process: melting, subliming, vaporizing

In the video, you can see that as heat is applied to a solid, it is converted into the liquid phase and then into the gas phase. This process can be studied by plotting the graph of temperature versus the time during which heat is applied to the system. Identify the states of matter and the processes that occur at each of the positions on the graph.

From lowest point on the graph to highest: Solid, Melting of a solid, Liquid, Boiling of the liquid, gas

In the video, you can see that when heat is applied to a solid it is converted into the liquid phase and then into the gas phase. This process can be studied by plotting the graph of temperature versus the time during which heat is applied to the system. Using this information, arrange the average kinetic energy of the molecules for the following options in decreasing order. Rank from highest to lowest. To rank items as equivalent, overlap them.

Highest to lowest: The average kinetic energy of the molecules after point d, The average kinetic energy of the molecules from point b to point c, the average kinetic energy of the molecules before point a

You are a researcher for a golf club manufacturer. You are given two identical looking cubes of a metal alloy. You are informed that they are made of the exact same material, but one is crystalline, whereas the other is amorphous. It is your job to determine which one is amorphous because this one is more stress-resistant and is useful in reinforcing golf clubs. Which of the following is the best way to determine which is which?

Melt both cubes and look for a broader range of melting temperatures. The one that melts over a broader range of temperatures is the amorphous solid. Melt both cubes and measure the range of melting temperatures. The one that melts over a narrower range of temperatures is the amorphous solid. *Determine the density of each cube. The less dense cube is the amorphous solid. Determine the density of each cube. The more dense one is the amorphous solid.

Rank the crystal lattice structures in order of decreasing efficiency of space in the structure. Rank from most to least efficient use of space. To rank items as equivalent, overlap them.

Most effective to least: Hexagonal close packing = face-centered cubic, body-centered cubic, simple cubic

The general form of a phase diagram is given below. Observe that this phase diagram is divided into three regions by the blue boundary lines similar to the way the interactive phase diagram for CO2 was divided. Compare this general form of this phase diagram with the interactive phase diagram for CO2 and classify points a through g on the phase diagram according to the number of phases present at each point.

One phase: a, b, c Two phases: e, d, f Three phases: g

An oxide of rhenium crystallizes with the unit cell depicted here (where rhenium = gray and oxygen = red)(Figure 1) . What is the formula of the oxide? Express your answer as a chemical formula.

ReO3

You are given six samples of carbon dioxide (CO2) that are stored at different temperatures and at different pressures. Using the interactive activity showing the phase diagram of CO2, determine the phases of each of the samples and classify them according to which phase they are in. Keep in mind that the temperature and pressure are not to scale. Drag the appropriate items to their respective bins.

Solid: -90degC and 72.9atm, -78.5degC and 5.1atm Liquid: 0degC and 72.9atm, 20degC and 60atm Gas: 20degC and 2atm, 31degC and 1atm

Consider the following two substances and their vapor pressures at 298 K. Substance Vapor pressure (mmHg) A 275 B 459 Based on this information, compare the characteristics of the two substances. Drag each item to the appropriate bin.

Substance A: Has a higher boiling point Has a higher heat of vaporization Substance B: Has weaker intermolecular forces Is a gas at 300 mmHg

Suppose that 0.48 g of water at 25∘C condenses on the surface of a 55-g block of aluminum that is initially at 25∘C. If the heat released during condensation goes only toward heating the metal, what is the final temperature (in degrees Celsius) of the metal block? (The specific heat capacity of aluminum, Cs,Al, is 0.903 J/(g⋅∘C).)

Tf = 49 ∘C

When a solid is placed in a container and heat is applied, a phase change occurs. Watch the video and identify which of the following statements are correct.

The average kinetic energy of the system changes while all of a solid is converted to a liquid. *When a solid is converted to a liquid, heat is absorbed. The temperature increases while all of a liquid is converted to a gas. When heat is applied to a solid, the molecular motion decreases as the temperature increases. *Temperature remains constant while all of a solid is converted to a liquid.

An oxide of titanium crystallizes with the following unit cell (titanium = gray; oxygen = red)(Figure 1) . What is the formula of the oxide? Express your answer as a chemical formula.

TiO2

X-rays with a wavelength of 1.64 Å scatter at an angle of 31.5 ∘ from a crystal. If n=1, what is the distance between planes of atoms in the crystal that give rise to this scattering? Express your answer with the appropriate units.

d = 1.57 Å

Calculate the amount of heat (in kilojoules) required to vaporize 2.58 kg of water at its boiling point.

q = 5830 kJ

What phase transition occurs when the pressure is decreased to 760 mmHg at constant temperature?

solid to liquid *liquid to gas liquid to solid solid to gas

How much heat is evolved in converting 1.00 mol of steam at 130.0 ∘C to ice at -50.0 ∘C? The heat capacity of steam is 2.01 J/(g⋅∘C) and of ice is 2.09 J/(g⋅∘C).

|Q| = 57.2 kJ

The vapor pressure of dichloromethane, CH2Cl2, at 0 ∘C is 134 mmHg. The normal boiling point of dichloromethane is 40. ∘C. Calculate its molar heat of vaporization. Express your answer to three significant figures and include the appropriate units.

ΔHvap = 30.9 kJ/mol