Chemistry, The Central Science , 10th edition

0 Midterm ReviewNuclear ChemistryGas LawsIntermolecular ForcesColligative PropertiesChemical Equilibrium Chemistry, The Central Science, 10th edition Theodore L. Brown, H. Eugene LeMay, Jr., and Bruce E. Bursten Donna Narsavage Heald Siena College Loudonville, NY  2006, Prentice-Hall

What change in the mass number of a nucleus occurs when the nucleus emits an alpha particle? • Mass number decreases by 1. • Mass number decreases by 2. • Mass number decreases by 4. • Mass number does not change.

Yes • No

Bonus: • Alpha rays most efficiently pass through the window. • Beta rays most efficiently pass through the window. • Gamma rays most efficiently pass through the window.

Indicate the number of protons (p) and neutrons (n) in the radioactive nucleus represented by: 60 27 Co 60 p, 27 n 33 p, 27 n 27 p, 33 n 27 p, 60 n None of the above

Correct Answer: 60 p, 27 n 33 p, 27 n 27 p, 33 n 27 p, 60 n None of the above The difference between the mass number and the atomic number is the number of neutrons (60  27) = 33.

K If the nucleus: undergoes positron emission it will become the isotope: 38 19 Potassium39 Argon38 Argon39 Calcium38 Calcium39

Correct Answer: Potassium39 Argon38 Argon39 Calcium38 Calcium39 The nuclear equation describing this process is given below: 38 19 K 38 18 0 1 Ar + e

Which of the following nuclei would you expect not to be radioactive?A band of stability is provided for reference. Carbon-14 Phosphorus-31 Iron-59 Radium-226 Uranium-235

Correct Answer: Carbon-14 Phosphorus-31 Iron-59 Radium-226 Uranium-235 Only phosphorus-31 is not outside the band of stability; its position is indicated by the red arrow.

How many (X) neutrons are required to balance the nuclear transmutation equation shown below? +  + + 1 235 142 91 1 n U Ba Kr X n 0 92 56 36 0 1 2 3 4 6

Correct Answer: 1 2 3 4 6 The balanced nuclear equation is given below: +  + + 1 235 142 91 1 n U Ba Kr 3 n 0 92 56 36 0

The isotope carbon-14 has a half-life of 5,715 years. How much of a 1.00 g sample of carbon-14 will exist after 34,290 years? 0.0156 g 0.0225 g 0.143 g 0.166 g None (all would have decayed).

12 Correct Answer: 0.0156 g 0.0225 g 0.143 g 0.166 g None (all would have decayed). 34,290 yr/5,715 yr = 6 Thus, six half-lives occur over this time. 1.00 g ( )6 = 1.00 g (1/64) = 0.0156 g

226Ra 222Rn The radioactive decay of Ra to Rn occurs with: • Loss of a neutron. • Gain of a proton. • Loss of electrons. • Loss of an alpha particle. • Gain of a positron.

Oxygen-15 is used as a radioactive tracer in medical imaging and has a half-life of 2.0 min. If the initial concentration of 15O is 16 mM, how long will it take for the concentration to be reduced to 1 mM? • 4 min • 6 min • 8 min • 10 min • 12 min

2 NO(g) + O2 (g) 2 NO2 (g) If 250 mL of NO is placed in a flask with O2, what volume of O2 is needed for complete reaction? • 100 mL • 125 mL • 200 mL • 250 mL • Cannot be determined from the given information.

If equal masses of CH4, C2H6, and C3H8 are placedin a flask, which of the following is true? • PCH4 = PC2H6 = PC3H8 • PCH4 ~ PC2H6 ~ PC3H8 • PCH4 > PC2H6 > PC3H8 • PCH4 < PC2H6< PC3H8 • None of the above

Gases are generally of very low molecular mass. • Gases have high kinetic energies. • In gases, the distance between molecules is relatively large. • In gases, the attractions between molecules are large.

Densities cannot be compared without additional amount and volume information. • Water vapor has the same density as N2 under the same conditions of temperature and pressure. • Water vapor is less dense than N2. • Water vapor is more dense than N2.

Additional pressure information is needed to compare average kinetic energies. • The heaviest gas (HCl) has the highest average kinetic energy and the other average kinetic energies decrease with molar mass. • HCl (298 K) and H2 (298 K) have the same average kinetic energy while O2 (350 K) has a lower average kinetic energy. • HCl (298 K) and H2 (298 K) have the same average kinetic energy while O2 (350 K) has a higher average kinetic energy.

Gases deviate from ideal behavior if their molar mass exceeds that of H2O. • Gases deviate from ideal behavior if the temperature is lower than room 298 K. • Gases deviate from ideal behavior because the molecules have finite sizes and there are some attractions between the molecules. • Gases deviate from ideal behavior if their normal boiling points are below room temperature and greater than the freezing point of H2O.

A gas initially at 2.0 atm is in an adjustable volume container of 10. L in volume. If the pressure is decreased to 0.50 atm, what is the new volume? 40. L 20. L 10. L 5.0 L

Correct Answer: 40. L 20. L 10. L 5.0 L 1 =  V constant P Thus, 2.00 atm(10. L) = 0.50 atm (Vfinal) Vfinal = 2.00 atm(10. L)/0.50 atm = 40. L

Assuming pressure is held constant, to what volume will a balloon initially at 1.0 L change if its temperature is decreased from 300 K to 75 K? 1.0 L 2.0 L 0.25 L 4.0 L

Correct Answer: 1.0 L 2.0 L 0.25 L 4.0 L =  V constant T Thus, 1.0 L/300 K = (Vfinal)/75 K Vfinal = 75 K/(1.0 L)300 K = 0.25 L

At standard temperature and pressure, how many moles of gas are present in a box with a volume of 112 L? 1.00 moles 2.00 moles 5.00 moles 0.200 moles

Correct Answer: 1.00 moles 2.00 moles 5.00 moles 0.200 moles = PV nRT ( ) ( ) ( ) nRT 1 mol 0.08206 L·atm/mol· K 273.15 K = = = V 22.41 L P 1.000 atm Thus, at STP 22.41 L = 112 L 1.00 mol n n = 5.00 moles

A container holds a mixture of oxygen, neon, and helium gases whose partial pressures are 150 torr, 300 torr, and 450 torr, respectively. The mole fraction of neon is • 0.17 • 0.33 • 0.50 • 0.67  = P P i i total

Correct Answer: • 0.17 • 0.33 • 0.50 • 0.67  = P P i i total Xi = Pi/Ptotal Xi = (300 torr)/(150 + 300 + 450) torr Xi = 300 torr/900 torr = 0.33

An unknown gas effuses at half the rate of helium. This gas is likely to be which of the following? H2 CH4 Ne O2 Ar

Correct Answer: H2 CH4 Ne O2 Ar (r1/2)2 =M2/M1 M2= (r1/r2)2M1 M2= (2/1)2(4.0 g/mol) = 16.0 g/mol Therefore it could be CH4

Real gases deviate from ideal behavior at __________ and _________. High temperature; low pressure Low temperature; high pressure High temperature; high pressure Low temperature; low pressure

Correct Answer: High temperature; low pressure Low temperature; high pressure High temperature; high pressure Low temperature; low pressure At low temperature and high pressure, intermolecular forces increase as the molecules get closer together.

Which of the following molecules can hydrogen bond with itself? • 1, 2 • 2, 3 • 3, 4 • 1, 2, 3 • 1, 2, 3, 4

Arrange the following according to increasing vapor pressure. NH3 I2 Br2 CH4 • NH3 < I2 < Br2 < CH4 • I2 < Br2 < NH3 < CH4 • NH3 < CH4 < I2 < Br2 • NH3 < I2 < CH4 < Br2 • CH4 < NH3 < Br2 < I2

800 600 Vapor Pressure (mm Hg) 400 200 0 0 25 50 75 100 Temperature ( ° C) Which statement is true? • Boiling point ~120°C • Boiling point ~95°C • Boiling point ~75°C • Melting point ~95°C • Melting point ~75°C

Chemistry, The Central Science , 10th edition