Q: A hydrogen atom's electron transitions from $n_i = 3$ to $n_f = 2$. Using the Bohr model equation $\Delta E = -2.18 \times 10^{-18} \left( \frac{1}{n_f^2} - \frac{1}{n_i^2} \right)$, what is the energy released in joules?

$\Delta E = -2.18 \times 10^{-18} \left( \frac{1}{2^2} - \frac{1}{3^2} \right) = -2.18 \times 10^{-18} \left( \frac{1}{4} - \frac{1}{9} \right) = -2.18 \times 10^{-18} \left( 0.25 - 0.111 \right) = -2.18 \times 10^{-18} \times 0.139 = -3.03 \times 10^{-19} \text{ J}$

Q: A sample contains 3.00 g of carbon. How many moles of carbon atoms are present? (Atomic mass of C = 12.01 g/mol)

$\text{Moles} = \frac{3.00\ \text{g}}{12.01\ \text{g/mol}} = 0.250\ \text{mol}$

Q: If a photon has a frequency of $5.00 \times 10^{14}$ Hz, what is its energy? ($h = 6.626 \times 10^{-34}$ J·s)

$E = h\nu = 6.626 \times 10^{-34} \times 5.00 \times 10^{14} = 3.31 \times 10^{-19}\ \text{J}$

Q: A sample contains two isotopes of chlorine: $^{35}$Cl (75.8%, mass = 34.97 amu) and $^{37}$Cl (24.2%, mass = 36.97 amu). What is the average atomic mass?

$\text{Average mass} = (0.758 \times 34.97) + (0.242 \times 36.97) = 26.52 + 8.95 = 35.47\ \text{amu}$

Q: Which conversion factor would you use to convert grams of water to moles of water?

$\frac{1\ \text{mol}}{18.02\ \text{g}}$

Q: A photon ejects an electron from a metal surface. If the photon energy is $5.00 \times 10^{-19}$ J and the binding energy is $2.00 \times 10^{-19}$ J, what is the kinetic energy of the ejected electron?

$\text{KE} = E_{\text{photon}} - E_{\text{binding}} = 5.00 \times 10^{-19} - 2.00 \times 10^{-19} = 3.00 \times 10^{-19}\ \text{J}$

Q: If you have 2.00 moles of sodium atoms, how many atoms do you have? ($1\ \text{mol} = 6.02 \times 10^{23}$ atoms)

$2.00 \times 6.02 \times 10^{23} = 1.20 \times 10^{24}$ atoms

Question 1

A hydrogen atom's electron transitions from $n_i = 3$ to $n_f = 2$. Using the Bohr model equation $\Delta E = -2.18 	imes 10^{-18} \left( \frac{1}{n_f^2} - \frac{1}{n_i^2} ight)$, what is the energy released in joules?

Accepted Answer

$\Delta E = -2.18 	imes 10^{-18} \left( \frac{1}{2^2} - \frac{1}{3^2} ight) = -2.18 	imes 10^{-18} \left( \frac{1}{4} - \frac{1}{9} ight) = -2.18 	imes 10^{-18} \left( 0.25 - 0.111 ight) = -2.18 	imes 10^{-18} 	imes 0.139 = -3.03 	imes 10^{-19} 	ext{ J}$

Question 2

Which law states that the ratio of the masses of elements in a compound is always the same, regardless of the sample size?

Accepted Answer

Law of Definite Proportions

Question 3

A sample contains 3.00 g of carbon. How many moles of carbon atoms are present? (Atomic mass of C = 12.01 g/mol)

Accepted Answer

$	ext{Moles} = \frac{3.00\ 	ext{g}}{12.01\ 	ext{g/mol}} = 0.250\ 	ext{mol}$

Question 4

Which equation is used to calculate the wavelength of a particle according to De Broglie's hypothesis?

Accepted Answer

$\lambda = \frac{h}{mv}$

Question 5

If a photon has a frequency of $5.00 	imes 10^{14}$ Hz, what is its energy? ($h = 6.626 	imes 10^{-34}$ J·s)

Accepted Answer

$E = h
u = 6.626 	imes 10^{-34} 	imes 5.00 	imes 10^{14} = 3.31 	imes 10^{-19}\ 	ext{J}$

Question 6

Which quantum number determines the shape of an atomic orbital?

Accepted Answer

Angular momentum quantum number ($l$)

Question 7

A sample contains two isotopes of chlorine: $^{35}$Cl (75.8%, mass = 34.97 amu) and $^{37}$Cl (24.2%, mass = 36.97 amu). What is the average atomic mass?

Accepted Answer

$	ext{Average mass} = (0.758 	imes 34.97) + (0.242 	imes 36.97) = 26.52 + 8.95 = 35.47\ 	ext{amu}$

Question 8

Which statement best describes the Heisenberg uncertainty principle?

Accepted Answer

It is impossible to simultaneously know the exact position and momentum of a particle.

Question 9

Which conversion factor would you use to convert grams of water to moles of water?

Accepted Answer

$\frac{1\ 	ext{mol}}{18.02\ 	ext{g}}$

Question 10

A photon ejects an electron from a metal surface. If the photon energy is $5.00 	imes 10^{-19}$ J and the binding energy is $2.00 	imes 10^{-19}$ J, what is the kinetic energy of the ejected electron?

Accepted Answer

$	ext{KE} = E_{	ext{photon}} - E_{	ext{binding}} = 5.00 	imes 10^{-19} - 2.00 	imes 10^{-19} = 3.00 	imes 10^{-19}\ 	ext{J}$

Question 11

Which of the following is NOT a criterion that defines a wave?

Accepted Answer

Density

Question 12

If you have 2.00 moles of sodium atoms, how many atoms do you have? ($1\ 	ext{mol} = 6.02 	imes 10^{23}$ atoms)

Accepted Answer

$2.00 	imes 6.02 	imes 10^{23} = 1.20 	imes 10^{24}$ atoms

Question 13

Which quantum number(s) determine the energy of an electron in a multi-electron atom?

Accepted Answer

Principal quantum number ($n$) and angular momentum quantum number ($l$)

Question 14

A student measures the mass of a sample as 4.50 g and the volume as 1.23 mL. What is the density, reported with the correct number of significant figures?

Accepted Answer

$	ext{Density} = \frac{4.50\ 	ext{g}}{1.23\ 	ext{mL}} = 3.66\ 	ext{g/mL}$

Question 15

If $n = 3$, what are the possible values for the angular momentum quantum number $l$?

Accepted Answer

$l = 0, 1, 2$

Question 16

A chemist needs to convert 250 mL to liters using the correct conversion factor. What is the answer?

Accepted Answer

$250\ 	ext{mL} 	imes \frac{1\ 	ext{L}}{1000\ 	ext{mL}} = 0.250\ 	ext{L}$

Question 17

Which law explains why two different compounds made from the same elements can have mass ratios that are simple whole number multiples of each other?

Accepted Answer

Law of Multiple Proportions

Question 18

A photon has a wavelength of $4.00 	imes 10^{-7}$ m. What is its energy? ($h = 6.626 	imes 10^{-34}$ J·s, $c = 3.00 	imes 10^8$ m/s)

Accepted Answer

$E = \frac{hc}{\lambda} = \frac{6.626 	imes 10^{-34} 	imes 3.00 	imes 10^8}{4.00 	imes 10^{-7}} = 4.97 	imes 10^{-19}\ 	ext{J}$

Essential General Chemistry Exam 1 Study Guide: Atoms, Quantum Mechanics, and Measurement

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