Q: Given the reaction $$3\text{Fe}_2\text{O}_3(s) + \text{CO}(g) \rightarrow 2\text{Fe}_3\text{O}_4(s) + \text{CO}_2(g)$$, and the following enthalpy changes: $$\Delta H_1$ = -24.8\ \text{kJ mol}^{-1}$$, $$\Delta H_2$ = -9.14\ \text{kJ mol}^{-1}$$, $$\Delta H_3$ = +11.0\ \text{kJ mol}^{-1}$$, what is the overall enthalpy change for the reaction?

$$\Delta H = -22.94\ \text{kJ mol}^{-1}$$

Q: For the hydrogen atom, what is the energy of the photon emitted when an electron transitions from $$n=4 to$$ $$n=2$$?

$$E = -2.18 \times 10$$^{-18}$$ \left( \frac{1}{2^2$} - \frac{1}{4^2$} \right)\ \text{J}$$

Q: What is the frequency of a photon with a wavelength of $$500\ \text{nm}$$?

$$\nu = \frac{c}{\lambda} = \frac{2.998 \times 10^8$\ \text{m/s}}{500 \times 10$$^{-9}$$\ \text{m}}$$

Q: If $$1.436\ \text{g} of $$benzoic acid ($$\text{MM} = 122.12\ \text{g mol}^{-1}) is $$burned in a bomb calorimeter with a heat capacity of $$9.425\ \text{kJ K}^{-1}$$ and initial temperature of $$25.000^\circ\text{C}$$, what is the final temperature if $$\$$Delta_{comb}$$H^\circ = -3222.0\ \text{kJ mol}^{-1}$$?

$$T_{final} = 25.000^\circ\text{C} + \frac{1.436/122.12 \times 3222.0}{9.425}$$

Question 1

Which of the following best describes the property of enthalpy ($$\Delta H) $$that allows you to calculate the enthalpy change for a reaction using either a series of thermochemical equations or heats of formation, and obtain the same result?

Accepted Answer

Enthalpy is a state function.

Question 2

Given the reaction $$3	ext{Fe}_2	ext{O}_3(s) + 	ext{CO}(g) ightarrow 2	ext{Fe}_3	ext{O}_4(s) + 	ext{CO}_2(g)$$, and the following enthalpy changes: $$\Delta H_1$ = -24.8\ 	ext{kJ mol}^{-1}$$, $$\Delta H_2$ = -9.14\ 	ext{kJ mol}^{-1}$$, $$\Delta H_3$ = +11.0\ 	ext{kJ mol}^{-1}$$, what is the overall enthalpy change for the reaction?

Accepted Answer

$$\Delta H = -22.94\ 	ext{kJ mol}^{-1}$$

Question 3

Which quantum number determines the shape of an atomic orbital?

Accepted Answer

Angular momentum quantum number ($$l)$$

Question 4

Sulphur has the electron configuration $$[Ne]3s^23$p^4$. Is sulphur paramagnetic or diamagnetic, and why?

Accepted Answer

Paramagnetic, because it has unpaired electrons in the $$3p$$ subshell.

Question 5

Why is an orbital in the $$2s$$ subshell lower in energy than an orbital in the $$2p$$ subshell, even though both have the same principal quantum number?

Accepted Answer

The $$2s$$ orbital penetrates closer to the nucleus, experiencing less shielding.

Question 6

For the hydrogen atom, what is the energy of the photon emitted when an electron transitions from $$n=4 to$$ $$n=2$$?

Accepted Answer

$$E = -2.18 	imes 10$$^{-18}$$ \left( \frac{1}{2^2$} - \frac{1}{4^2$} ight)\ 	ext{J}$$

Question 7

What is the frequency of a photon with a wavelength of $$500\ 	ext{nm}$$?

Accepted Answer

$$
u = \frac{c}{\lambda} = \frac{2.998 	imes 10^8$\ 	ext{m/s}}{500 	imes 10$$^{-9}$$\ 	ext{m}}$$

Question 8

If the energy of a photon emitted during a transition in Be$$^{2+}$$ ions is calculated using $$E = -2.18 	imes 10$$^{-18}$$ Z^2$ \left( \frac{1}{n_f^2$} - \frac{1}{n_i^2$} ight)$$, what is the value of $$Z$$ for Be$$^{2+}$$?

Accepted Answer

$$Z = 4$$

Question 9

Visible light has a wavelength between $$400$$ and $$750\ 	ext{nm}. $$Would you expect the photons emitted by the Be$$^{2+}$$ transition from $$n=4 to$$ $$n=2 to be $$visible? Justify your answer.

Accepted Answer

No, because the energy difference is much larger, resulting in a photon in the ultraviolet region.

Question 10

A bomb calorimeter is used to determine $$\Delta U_{rxn}. $$Why can work ($$w) be $$ignored in the calculation?

Accepted Answer

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

Question 11

If $$1.436\ 	ext{g} of $$benzoic acid ($$	ext{MM} = 122.12\ 	ext{g mol}^{-1}) is $$burned in a bomb calorimeter with a heat capacity of $$9.425\ 	ext{kJ K}^{-1}$$ and initial temperature of $$25.000^\circ	ext{C}$$, what is the final temperature if $$\$$Delta_{comb}$$H^\circ = -3222.0\ 	ext{kJ mol}^{-1}$$?

Accepted Answer

$$T_{final} = 25.000^\circ	ext{C} + \frac{1.436/122.12 	imes 3222.0}{9.425}$$

Question 12

Which of the following is the correct formula for the change in internal energy of a system?

Accepted Answer

$$\Delta U = q + w$$

Question 13

How many radial nodes are present in a $$3p$$ orbital?

Accepted Answer

1

Question 14

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

Accepted Answer

Neon (Ne)

Question 15

What is the correct electron configuration for Vanadium (V)?

Accepted Answer

$$[Ar] 4s^2$ 3d^3$

Question 16

Which formula is used to calculate the pressure of a mixture of volatile liquids?

Accepted Answer

$$P_{total} = X_A P_A^* + X_B P_B^*$$

Question 17

Which of the following best explains why significant digits are important in reporting numerical answers in chemistry?

Accepted Answer

They reflect the precision of the measurement and calculations.

Question 18

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

Accepted Answer

$$E = h 
u$$

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

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