Question 1

A 2.00 L container holds a mixture of nitrogen gas (N$$_2) $$and oxygen gas (O$$_2) at 25$$°C and a total pressure of 1.00 atm. If the partial pressure of N$$_2 is 0.70 $$atm, what is the mole fraction of O$$_2 in $$the mixture?

Accepted Answer

$$0.30$$

Question 2

Which of the following statements best describes an exothermic reaction?

Accepted Answer

The system releases heat to the surroundings, and $$\Delta H is $$negative.

Question 3

A sample of gas occupies 4.00 L at 1.00 atm and 300 K. If the pressure is increased to 2.00 atm and the temperature is increased to 400 K, what is the new volume of the gas? (Assume ideal gas behavior.)

Accepted Answer

$$2.67\ \mathrm{L}$$

Question 4

Which of the following is the correct oxidation number for sulfur in the ion SO$$_4$$^{2-}$$?

Accepted Answer

$$+6$$

Question 5

A reaction has $$\Delta H = -125\ \mathrm{kJ}. $$Which of the following statements is true?

Accepted Answer

The reaction is exothermic and releases 125 kJ of heat.

Question 6

Which of the following best describes the role of the oxidant in a redox reaction?

Accepted Answer

It is the species that is reduced and causes another species to be oxidized.

Question 7

A 50.0 g sample of water at 25.0°C absorbs 4184 J of heat. What is the final temperature of the water? (Specific heat of water = $$4.18\ \mathrm{J/g\cdot K})$$

Accepted Answer

$$45.0^\circ \mathrm{C}$$

Question 8

Which of the following gases will have the highest average molecular speed at 298 K?

Accepted Answer

Helium ($$\mathrm{He})$$

Question 9

A reaction is carried out in a coffee-cup calorimeter. If the temperature of the solution increases, which of the following is true?

Accepted Answer

The reaction is exothermic and $$q_{\mathrm{rxn}} is $$negative.

Question 10

Which of the following is NOT a correct statement about the kinetic molecular theory of gases?

Accepted Answer

Gas particles lose energy when they collide with each other.

Question 11

A 0.500 mol sample of an unknown gas has a mass of 16.0 g at 1.00 atm and 273 K. What is the molar mass of the gas?

Accepted Answer

$$32.0\ \mathrm{g/mol}$$

Question 12

Which of the following is the correct relationship for Boyle’s Law?

Accepted Answer

$$P_1V_1 = P_2V_2$$

Question 13

A reaction has $$q = -250\ \mathrm{J}$$ and $$w = +50\ \mathrm{J}. $$What is $$\Delta E$$ for the system?

Accepted Answer

$$-200\ \mathrm{J}$$

Question 14

Which of the following is the correct conversion between calories and joules?

Accepted Answer

$$1\ \mathrm{cal} = 4.184\ \mathrm{J}$$

Question 15

Which of the following is the limiting reactant when 2.0 mol of H$$_2$$ reacts with 1.0 mol of O$$_2 to $$form water according to the equation: $$2\mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2\mathrm{H}_2\mathrm{O}$$?

Accepted Answer

H$$_2$$

Question 16

Which of the following is a strong electrolyte when dissolved in water?

Accepted Answer

NaCl

Question 17

If a reaction has a percent yield of 80.0% and the theoretical yield is 10.0 g, what is the actual yield?

Accepted Answer

$$8.00\ \mathrm{g}$$

Question 18

Which of the following best describes the conservation of energy in a chemical reaction?

Accepted Answer

The total energy of the system and surroundings remains constant.

Question 19

Given the following thermochemical equations:

$$\mathrm{C}(s) + \frac{1}{2}\mathrm{O}_2(g) \rightarrow \mathrm{CO}(g)\ \ \Delta H_1$ = -110.5\ \mathrm{kJ}$$

$$\mathrm{CO}(g) + \frac{1}{2}\mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g)\ \ \Delta H_2$ = -283.0\ \mathrm{kJ}$$

What is $$\Delta H$$ for the reaction: $$\mathrm{C}(s) + \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g)$$?

Accepted Answer

$$-393.5\ \mathrm{kJ}$$

Question 20

Which of the following is the correct formula for calculating the density of a gas using the ideal gas law?

Accepted Answer

$$\rho = \frac{PM}{RT}$$

General Chemistry: Exam 3 Study Guide – Gases and Thermochemistry

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