Q: For the hydrogen atom, what is the energy (in kJ/mol) of a photon emitted when an electron transitions from $$n=4 to$$ $$n=2$$? Use $$E = -2.179 \times 10$$^{-18}$$\ \mathrm{J}\ (\frac{1}{n_f^2$} - \frac{1}{n_i^2$})$$ and Avogadro's number $$6.022 \times 10$$^{23}$$\ \mathrm{mol}^{-1}.$$

$$-4.09 \times 10^2$\ \mathrm{kJ\ $$mol^{-1}$$}$$

Question 1

Which of the following statements best describes Hess's Law, as applied to enthalpy changes in chemical reactions?

Accepted Answer

The enthalpy change of a reaction is the same, regardless of the number of steps or the pathway taken, as long as the initial and final conditions are the same.

Question 2

Given the following thermochemical equations:

$$\mathrm{Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g)}$$  $$\Delta H = -24.8\ \mathrm{kJ\ $$mol^{-1}$$}$$
$$\mathrm{Fe_2O_3(s) \rightarrow 2FeO(s) + 0.5O_2(g)}$$  $$\Delta H = +94.4\ \mathrm{kJ\ $$mol^{-1}$$}$$
$$\mathrm{FeO(s) + CO(g) \rightarrow Fe(s) + CO_2$(g)}$$  $$\Delta H = -11.0\ \mathrm{kJ\ $$mol^{-1}$$}$$

What is the enthalpy change for the reaction: $$\mathrm{Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g)}$$ using Hess's Law?

Accepted Answer

$$\Delta H = -24.8\ \mathrm{kJ\ $$mol^{-1}$$}$$

Question 3

Which of the following sets of quantum numbers is NOT allowed for an electron in an atom?

Accepted Answer

$$n = 2,\ l = 2,\ m_l = 1,\ m_s = +\frac{1}{2}$$

Question 4

Which of the following ions is isoelectronic with argon ($$\mathrm{Ar}$$)?

Accepted Answer

$$\mathrm{K^+}$$

Question 5

A student is asked to draw the orbital filling diagram for sulfur ($$\mathrm{S}$$, atomic number 16). Which of the following is the correct electron configuration?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^4$$

Question 6

Which of the following best explains why the 2s orbital is lower in energy than the 2p orbital in a multi-electron atom?

Accepted Answer

The 2s orbital is closer to the nucleus and experiences less shielding from inner electrons.

Question 7

For the hydrogen atom, what is the energy (in kJ/mol) of a photon emitted when an electron transitions from $$n=4 to$$ $$n=2$$? Use $$E = -2.179 	imes 10$$^{-18}$$\ \mathrm{J}\ (\frac{1}{n_f^2$} - \frac{1}{n_i^2$})$$ and Avogadro's number $$6.022 	imes 10$$^{23}$$\ \mathrm{mol}^{-1}.$$

Accepted Answer

$$-4.09 	imes 10^2$\ \mathrm{kJ\ $$mol^{-1}$$}$$

Question 8

Which of the following transitions in the hydrogen atom would emit a photon in the visible region (400–750 nm)?

Accepted Answer

$$n=3 to$$ $$n=2$$

Question 9

A bomb calorimeter is used to determine the enthalpy change of combustion for benzoic acid. If $$1.436\ \mathrm{g} of $$benzoic acid ($$\mathrm{C_7H_6O_2}$$, $$\mathrm{M_{r}} = 122.12\ \mathrm{g\ $$mol^{-1}$$}) is $$burned and the heat capacity of the calorimeter is $$9.425\ \mathrm{kJ\ ^\circ C$$^{-1}$$}$$, what is the temperature change if $$\Delta H_{comb} = -3222.0\ \mathrm{kJ\ $$mol^{-1}$$}$$?

Accepted Answer

$$0.50\ ^\circ \mathrm{C}$$

Question 10

Which of the following best explains why $$w ($$work) can be ignored in the calculation of $$\Delta U in a $$bomb calorimeter?

Accepted Answer

Because the volume of the system is constant, so $$w = -P\Delta V = 0.$$

Question 11

Which of the following statements about significant figures is correct when reporting the result of a calculation involving multiplication and division?

Accepted Answer

The result should have as many significant figures as the value with the fewest significant figures.

Question 12

Which of the following best describes a paramagnetic atom?

Accepted Answer

An atom with one or more unpaired electrons.

Question 13

Which of the following elements has the highest first ionization energy?

Accepted Answer

Neon ($$\mathrm{Ne})$$

Question 14

Which of the following best describes the relationship between the number of angular nodes and the quantum numbers $$n$$ and $$l$$?

Accepted Answer

Number of angular nodes = $$l$$

Question 15

Which of the following is the correct formula for the energy of a photon?

Accepted Answer

$$E = h 
u$$

Question 16

Which of the following best explains why the emission spectrum of hydrogen consists of discrete lines?

Accepted Answer

Because electrons in hydrogen can only occupy specific energy levels, and transitions between these levels emit photons of specific energies.

Question 17

Which of the following is the correct relationship for the frequency ($$
u) of a $$photon given its wavelength ($$\lambda) $$and the speed of light ($$c$$)?

Accepted Answer

$$
u = \frac{c}{\lambda}$$

Question 18

Which of the following best describes the difference between a 2s and a 2p orbital?

Accepted Answer

A 2s orbital has one spherical node, while a 2p orbital has one angular node.

General Chemistry 1050: Thermochemistry, Atomic Structure, and Quantum Theory Study Notes

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