Q: Which of the following is the correct expression for the enthalpy change of a reaction using standard enthalpies of formation?

$$\Delta H^\circ_{rxn} = \sum n \Delta H^\circ_f(\text{products}) - \sum n \Delta H^\circ_f(\text{reactants})$$

Q: A photon has a wavelength of $$500\ \mathrm{nm}. $$What is its frequency? (Speed of light $$c = 3.00 \times 10^8$\ \mathrm{m/s})$$

$$6.00 \times 10$$^{14}$$\ \mathrm{Hz}$$

Question 1

A 2.00 L container holds a mixture of nitrogen and oxygen gases at 300 K and a total pressure of 1.00 atm. If the partial pressure of nitrogen is 0.70 atm, what is the mole fraction of oxygen in the mixture?

Accepted Answer

$$0.30$$

Question 2

Which of the following statements best explains why the ideal gas law fails at very high pressures and low temperatures?

Accepted Answer

Intermolecular forces and the finite volume of gas particles become significant.

Question 3

A sample of helium gas effuses through a small hole in 50 seconds. Under the same conditions, an unknown gas takes 100 seconds to effuse. What is the molar mass of the unknown gas? (Molar mass of He = 4.00 g/mol)

Accepted Answer

$$16.0\ \mathrm{g/mol}$$

Question 4

Which of the following best describes the energy change when a system absorbs 200 J of heat and does 50 J of work on the surroundings?

Accepted Answer

$$\Delta E = 150\ \mathrm{J}$$

Question 5

Which of the following is a correct statement of the first law of thermodynamics?

Accepted Answer

$$\Delta E = q + w$$

Question 6

A 100.0 g sample of water is heated from $$25.0^\circ\mathrm{C} to$$ $$75.0^\circ\mathrm{C}. If $$the specific heat capacity of water is $$4.18\ \mathrm{J/g\cdot K}$$, how much heat is absorbed?

Accepted Answer

$$20,900\ \mathrm{J}$$

Question 7

Which of the following best explains why all gases at the same temperature have the same average kinetic energy?

Accepted Answer

Kinetic energy depends only on temperature, not on the identity of the gas.

Question 8

Which equation would you use to calculate the root mean square velocity of a gas molecule?

Accepted Answer

$$u_{rms} = \sqrt{\dfrac{3RT}{M}}$$

Question 9

A gas sample is collected over water at $$25^\circ\mathrm{C}$$ and a total pressure of $$760\ \mathrm{mmHg}. $$The vapor pressure of water at this temperature is $$24\ \mathrm{mmHg}. $$What is the partial pressure of the dry gas?

Accepted Answer

$$736\ \mathrm{mmHg}$$

Question 10

Which of the following best describes the photoelectric effect?

Accepted Answer

Electrons are ejected from a metal surface when it is exposed to light of sufficient frequency.

Question 11

Which of the following equations correctly relates the energy of a photon to its frequency?

Accepted Answer

$$E = h 
u$$

Question 12

Which quantum number determines the shape of an atomic orbital?

Accepted Answer

Angular momentum quantum number ($$l)$$

Question 13

A chemical reaction in a bomb calorimeter releases $$500\ \mathrm{J} of $$heat. What is the value of $$q_{v}$$ for this reaction?

Accepted Answer

$$-500\ \mathrm{J}$$

Question 14

Which of the following best describes the difference between an endothermic and an exothermic reaction?

Accepted Answer

Endothermic reactions absorb heat; exothermic reactions release heat.

Question 15

Which of the following is the correct expression for the enthalpy change of a reaction using standard enthalpies of formation?

Accepted Answer

$$\Delta H^\circ_{rxn} = \sum n \Delta H^\circ_f(	ext{products}) - \sum n \Delta H^\circ_f(	ext{reactants})$$

Question 16

Which of the following best describes the Heisenberg Uncertainty Principle?

Accepted Answer

It is impossible to know both the exact position and momentum of an electron simultaneously.

Question 17

Which of the following is the correct relationship between the wavelength ($$\lambda$$), frequency ($$
u$$), and speed of light ($$c$$)?

Accepted Answer

$$c = \lambda 
u$$

Question 18

A photon has a wavelength of $$500\ \mathrm{nm}. $$What is its frequency? (Speed of light $$c = 3.00 	imes 10^8$\ \mathrm{m/s})$$

Accepted Answer

$$6.00 	imes 10$$^{14}$$\ \mathrm{Hz}$$

Question 19

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

Accepted Answer

Electrons in hydrogen atoms can only occupy specific energy levels.

Question 20

Which of the following is the correct formula for the energy change when an electron in a hydrogen atom transitions from $$n_i to$$ $$n_f$$?

Accepted Answer

$$\Delta E = -2.18 	imes 10$$^{-18}$$ \left( \dfrac{1}{n_f^2$} - \dfrac{1}{n_i^2$} ight)\ \mathrm{J}$$

General Chemistry Study Guide: Gases, Thermochemistry, and Quantum-Mechanical Model of the Atom

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