Post-Lecture Assignment Chapter 6

A gas at 750 mmHg and 27 C has a density of 2.32 g/Lg. Which of the following could it be? CO2 Kr H2S C4H10

C4H10

What is the mass in grams of one molar volume of each of the gases? H2

2.02 g

What is the mass in grams of one molar volume of each of the gases? C2H4

28.1 g

What is the mass in grams of one molar volume of each of the gases? Ar

39.948 g

Imagine that you have an ideal gas in a 7.70 L container, and that 2150 molecules of this gas collide with a square-inch area of the container at any given instant. If the volume is increased to 38.5 L at constant temperature, how many collisions will occur per square inch of this larger container?

430

When a solid is placed in a container and heat is applied, a phase change occurs. Watch the video and sort the parts of the curve based on whether the average energy of the molecules is changing, or is constant.

Average molecule energy change The liquid is heated to reach the boiling point The solid is heated to reach the melting point Average molecule energy constant The solid is heated at the melting point The liquid is heated at the boiling point

Which of the following would you expect to dissolve in carbon tetrachloride (CCl4)? NaCl C8H18 C5H12 Li2CO3

C8H18 C5H12

What intermolecular forces are present in each of the substances?

DISPERSION ONLY: C_5H_12C_4H_10 Dispersion forces and dipole-dipole forces: HCN Dispersion forces, dipole-dipole forces, and hydrogen bonding: NH_3 C_2H_5OH

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 which of the following substances are dipole-dipole forces an important intermolecular force?

HBr

Explain why KNO3will not dissolve in hexane.

Hexane is nonpolar, but KNO3 is an ionic compound. There is not an existing interactions between the solvent and the ions of the solid which would pull the ions out of the crystal lattice. So, KNO3 will not dissolve in hexane.

Arrange the molecules in order of decreasing boiling point.

Highest boiling point H2O HBr H2 Lowest boiling point

Three identical 10 L tanks contain 6 mol of helium (He) at 293 K. The pressure in each of the tanks is increased as described below: Tank A: The tank volume is decreased from 10 L to 5 L while the temperature and the number of moles of HeHe remain constant. Tank B: The tank temperature is increased from 293 K to 308 K while the volume and the number of moles of HeHe remain constant. Tank C: The number of moles of HeHe in the tank is increased from 6 mol to 9 mol while the temperature and the volume remain constant.How is the average kinetic energy, KE, of the He molecules affected in each case?

KE increases Tank B KE stays constant Tank A Tank C

Calculate the molar mass of a gas that has a density of 1.98 g/L at STP

M = 44.4 gmol

Calculate the molar mass of an unknown liquid for which 3.33 L of its vapor at STP weighs 10.88 g.

M= 73.2 gmol

Which of the following would you expect to dissolve in water? (Choose all that apply!) NaCl C8H18 C5H12 Li2CO3

NaCl Li2CO3

An electrolyte is a substance that will conduct electricity when dissolved in water. A substance that conducts electricity well is a strong electrolyte. A substance that conducts electricity poorly is a weak electrolyte. In contrast, a substance that does not conduct electricity when dissolved in water is a nonelectrolyte. Watch the video about the electrolytic properties of sodium chloride, NaCl, and sugar. Watch the animation, then check off the samples that will conduct electricity.

NaCl solution

Hexane (C6H14) is a nonpolar solvent. Would you expect KNO3 to dissolve in hexane?

No, KNO3 will not dissolve in hexane.

If the volume of the original sample in Part A (P1 = 662 torr, V1V1V_1 = 40.0 L ) changes to 67.0 L , without a change in the temperature or moles of gas molecules, what is the new pressure, P2P?

P2 = 395 torr

Consider 4.70 L of a gas at 365 mmHg and 20 ∘C . If the container is compressed to 2.20 L and the temperature is increased to 30 ∘C , what is the new pressure, P2, inside the container? Assume no change in the amount of gas inside the cylinder.

P2= 806 mmHg

What are the five basic postulates of kinetic-molecular theory?

Particles of a gas are in rapid, constant motion and move in straight lines. The particles of a gas are tiny compared with the distances between them. Because the particles of a gas are so far apart, there is very little attraction between them. Particles of a gas collide with one another. Energy is conserved in these collisions; energy lost by one particle is gained by the other. Temperature is a measure of the average kinetic energy of the gas particles.

A 10.0 L gas cylinder is filled with 10.0 moles of gas. The tank is stored at 13 ∘C. What is the pressure in the tank?

Ptank = 23.5 atm

Classify the following phase changes as releasing energy or absorbing energy.

Releasing energy deposition condensing freezing Absorbing energy melting vaporizing subliming

What Celsius temperature, T2_2, is required to change the volume of the gas sample in Part A (T1 = 31 ∘C∘, V1= 1240 L ) to a volume of 2480 L ? Assume no change in pressure or the amount of gas in the balloon.

T2 = 335 ∘C

Which postulate best explains why a gas can be compressed?

The particles of a gas are tiny compared with the distances between them.

According to the kinetic-molecular theory, what change in pressure occurs when the particles of a gas strike the walls of the container less often?

The pressure decreases.

Will the pressure of a fixed amount of a gas increase, decrease, or remain unchanged with a decrease in volume at constant temperature?

The pressure of a gas will increase.

Will the pressure of a fixed amount of a gas increase, decrease, or remain unchanged with an increase in temperature at constant volume?

The pressure of a gas will increase.

Will the pressure of a fixed amount of a gas increase, decrease, or remain unchanged with an increase in temperature coupled with a decrease in volume?

The pressure of a gas will increase.

According to the kinetic-molecular theory, what change in temperature occurs if the particles of a gas begin to move more slowly, on average?

The temperature decreases.

A 12.0 L gas cylinder has been filled with 5.20 moles of gas. You measure the pressure to be 3.40 atm. What is the temperature inside the tank?

Ttank = -177 ∘C∘

A cylinder, with a piston pressing down with a constant pressure, is filled with 2.10 molesof a gas (n1), and its volume is 46.0 L (V1). If 0.800 mole of gas leak out, and the pressure and temperature remain the same, what is the final volume of the gas inside the cylinder?

V2 = 28.5 L

A sample of ideal gas at room temperature occupies a volume of 40.0 LL at a pressure of 662 torr . If the pressure changes to 3310 torr , with no change in the temperature or moles of gas, what is the new volume, V2?

V2 = 8.00 L

A sample of gas in a balloon has an initial temperature of 31 ∘C and a volume of 1240 L . If the temperature changes to 85 ∘C, and there is no change of pressure or amount of gas, what is the new volume, V2 of the gas?

V2= 1460 L

A very flexible helium-filled balloon is released from the ground into the air at 20. ∘C. The initial volume of the balloon is 5.00 L, and the pressure is 760 mmHg. The balloon ascends to an altitude of 20 km, where the pressure is 76.0 mmHg and the temperature is −50∘C. What is the new volume, V2V, of the balloon in liters, assuming it doesn't break or leak?

V2= 38.1 L

A balloon is floating around outside your window. The temperature outside is 23 ∘C , and the air pressure is 0.700 atm . Your neighbor, who released the balloon, tells you that he filled it with 3.10 moles of gas. What is the volume of gas inside this balloon?

Vballoon = 108 L

Calculate the density, in grams per liter, of carbon dioxide gas at STP.

dCO2 = 1.96 gL

What type of intermolecular interaction predominates in the following substances? propane (C3H8) hydrogen fluoride (HF) helium (He) potassium chloride (KCl)

dispersion forces hydrogen bonding dispersion forces ionic bonds

A sample of gas in a cylinder as in the example in Part A has an initial volume of 56.0 L , and you have determined that it contains 1.90 moles of gas. The next day you notice that some of the gas has leaked out. The pressure and temperature remain the same, but the volume has changed to 14.0 L . How many moles of gas (n2) remain in the cylinder?

n2= 0.475 mole

A 200 L kiln is used for vitrifying ceramics. It is currently operating at 1235 ∘C, and the pressure is 1.100 atm. How many moles of air molecules are within the confines of the kiln?

nair = 1.78 mol

Give two examples of solvents previously used in industrial processes that have been replaced by scCO2.

perchloroethylene methylene chloride

In addition to Green Chemistry Principles 3 and 5, how else might the use of an environmentally friendly solvent like scCO2 impact green chemistry?

scCO2 is easily recycled.