Q: Which of the following is the correct relationship for calculating the enthalpy change ($$\Delta H) $$using Hess’s Law?

$$\Delta H_{\text{overall}} = \sum \Delta H_{\text{steps}}$$

Question 1

Which of the following best describes an oxidation-reduction (redox) reaction?

Accepted Answer

A reaction in which electrons are transferred between species.

Question 2

In the reaction $$ \ce{2Na + Cl2 -\u003e 2NaCl} $$, which species is oxidized?

Accepted Answer

Na

Question 3

A sample of gas occupies 10.0 L at 2.00 atm and 300 K. What will be its volume at 1.00 atm and 300 K, assuming the amount of gas remains constant?

Accepted Answer

$$20.0\ \mathrm{L}$$

Question 4

Which of the following is the correct expression for the ideal gas law?

Accepted Answer

$$PV = nRT$$

Question 5

A mixture contains 2.0 mol of O$$_2$$ and 3.0 mol of N$$_2. $$What is the mole fraction of O$$_2 in $$the mixture?

Accepted Answer

$$0.40$$

Question 6

Which of the following statements about Graham’s Law of Effusion is correct?

Accepted Answer

The rate of effusion of a gas is inversely proportional to the square root of its molar mass.

Question 7

Which of the following is NOT a postulate of the kinetic molecular theory of gases?

Accepted Answer

Gas particles exert attractive and repulsive forces on each other.

Question 8

A 5.00 g sample of an unknown gas effuses in 10.0 minutes. Under identical conditions, 5.00 g of O$$_2$$ effuses in 8.0 minutes. What is the molar mass of the unknown gas? (Molar mass of O$$_2 = 32.0 g/$$mol)

Accepted Answer

$$50.0\ \mathrm{g/mol}$$

Question 9

Which of the following best describes an exothermic reaction?

Accepted Answer

A reaction that releases heat to the surroundings.

Question 10

According to the first law of thermodynamics, which of the following equations is correct for the change in internal energy ($$\Delta E) of a $$system?

Accepted Answer

$$\Delta E = q + w$$

Question 11

A chemical reaction occurs in a bomb calorimeter. The temperature of the calorimeter increases by $$2.50\ ^\circ\mathrm{C}$$, and the heat capacity of the calorimeter is $$5.00\ \mathrm{kJ}/^\circ\mathrm{C}. $$What is the heat released by the reaction?

Accepted Answer

$$12.5\ \mathrm{kJ}$$

Question 12

Which of the following is a state function?

Accepted Answer

Internal energy ($$E)$$

Question 13

Which of the following best explains why the volume of a gas increases when the temperature increases at constant pressure?

Accepted Answer

The gas particles move faster and collide with the walls more frequently, causing the volume to expand.

Question 14

A 1.00 mol sample of an ideal gas at STP occupies what volume?

Accepted Answer

$$22.4\ \mathrm{L}$$

Question 15

Which of the following is the correct relationship for calculating the enthalpy change ($$\Delta H) $$using Hess’s Law?

Accepted Answer

$$\Delta H_{	ext{overall}} = \sum \Delta H_{	ext{steps}}$$

Question 16

Which of the following is the correct equation for calculating the heat absorbed or released by a substance?

Accepted Answer

$$q = m c \Delta T$$

Question 17

A gas sample is collected over water at 25$$^\circC. $$The total pressure is 755 mmHg, and the vapor pressure of water at this temperature is 24 mmHg. What is the partial pressure of the dry gas?

Accepted Answer

$$731\ \mathrm{mmHg}$$

Question 18

Which of the following best describes the law of conservation of energy?

Accepted Answer

Energy cannot be created or destroyed, only transformed from one form to another.

Question 19

Which of the following is the correct van der Waals equation for real gases?

Accepted Answer

$$(P + \dfrac{a n^2$}{V^2$})(V - nb) = nRT$$

Question 20

A reaction has $$\Delta H = -150\ \mathrm{kJ}$$ and $$\Delta E = -145\ \mathrm{kJ}. If $$the reaction occurs at constant pressure and produces 2.0 L of gas at 1.0 atm, how much work is done by the system? ($$1\ \mathrm{L} \cdot \mathrm{atm} = 101\ \mathrm{J})$$

Accepted Answer

$$-202\ \mathrm{J}$$

General Chemistry Exam Study Guide: Gases, Thermodynamics, and Calorimetry

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