Q: A 50.0 g sample of water is heated from $$20.0\ ^\circ\mathrm{C} to$$ $$70.0\ ^\circ\mathrm{C}. $$The specific heat capacity of water is $$4.18\ \mathrm{J/g\cdot ^\circ C}. $$How much heat ($$q) is $$absorbed by the water?

$$q = 50.0 \times 4.18 \times (70.0 - 20.0) = 10,450\ \mathrm{J}$$

Q: Given the reaction $$2\mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2\mathrm{H}_2\mathrm{O}(l)$$ with $$\Delta H = -571.6\ \mathrm{kJ}$$, how much heat is released when 4.00 g of $$\mathrm{H}_2$$ reacts completely?

$$-571.6\ \mathrm{kJ} \times \frac{4.00\ \mathrm{g}/2.02\ \mathrm{g/mol}}{2\ \mathrm{mol}} = -566\ \mathrm{kJ}$$

Question 1

Which of the following statements best describes the First Law of Thermodynamics?

Accepted Answer

The total energy of the universe remains constant; energy can be transferred or transformed but not created or destroyed. $$\Delta E = q + w$$

Question 2

A 50.0 g sample of water is heated from $$20.0\ ^\circ\mathrm{C} to$$ $$70.0\ ^\circ\mathrm{C}. $$The specific heat capacity of water is $$4.18\ \mathrm{J/g\cdot ^\circ C}. $$How much heat ($$q) is $$absorbed by the water?

Accepted Answer

$$q = 50.0 	imes 4.18 	imes (70.0 - 20.0) = 10,450\ \mathrm{J}$$

Question 3

Which of the following processes is exothermic?

Accepted Answer

Condensation of steam

Question 4

Given the reaction $$2\mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2\mathrm{H}_2\mathrm{O}(l)$$ with $$\Delta H = -571.6\ \mathrm{kJ}$$, how much heat is released when 4.00 g of $$\mathrm{H}_2$$ reacts completely?

Accepted Answer

$$-571.6\ \mathrm{kJ} 	imes \frac{4.00\ \mathrm{g}/2.02\ \mathrm{g/mol}}{2\ \mathrm{mol}} = -566\ \mathrm{kJ}$$

Question 5

Which of the following best explains why hydrogen bonding only occurs when hydrogen is bonded to N, O, or F?

Accepted Answer

N, O, and F are highly electronegative and small, creating a strong dipole and allowing close approach for strong hydrogen bonding.

Question 6

A gas sample occupies $$2.50\ \mathrm{L} at$$ $$1.00\ \mathrm{atm}$$ and $$300\ \mathrm{K}. $$What volume will it occupy at $$2.00\ \mathrm{atm}$$ and $$300\ \mathrm{K}$$, assuming ideal behavior?

Accepted Answer

$$1.25\ \mathrm{L}$$

Question 7

Which of the following statements about real gases is correct?

Accepted Answer

Real gases deviate most from ideal behavior at low temperature and high pressure due to intermolecular forces and finite molecular volume.

Question 8

Which of the following best describes the relationship between vapor pressure and boiling point?

Accepted Answer

A liquid boils when its vapor pressure equals the external pressure.

Question 9

Which of the following is the strongest intermolecular force present in liquid ammonia ($$\mathrm{NH}_3$$)?

Accepted Answer

Hydrogen bonding

Question 10

A solution is prepared by dissolving $$0.50\ \mathrm{mol} of $$NaCl in $$1.00\ \mathrm{kg} of $$water. What is the expected van’t Hoff factor ($$i) $$for NaCl?

Accepted Answer

$$i = 2$$

Question 11

Which of the following best describes the effect of increasing temperature on the rate of a chemical reaction?

Accepted Answer

The rate increases because more molecules have sufficient energy to overcome the activation energy barrier.

Question 12

Given the following reaction at equilibrium: $$\mathrm{N}_2(g) + 3\mathrm{H}_2(g) \rightleftharpoons 2\mathrm{NH}_3(g)$$, what will happen if the pressure is increased by decreasing the volume?

Accepted Answer

The equilibrium will shift toward the side with fewer moles of gas (toward ammonia).

Question 13

Which of the following is a colligative property?

Accepted Answer

Boiling point elevation

Question 14

A reaction has a rate law $$	ext{rate} = k[\mathrm{A}]^2[\mathrm{B}]. $$What is the overall order of the reaction?

Accepted Answer

Third order

Question 15

Which of the following best describes the difference between intermolecular and intramolecular forces?

Accepted Answer

Intermolecular forces are forces between molecules; intramolecular forces are forces within a molecule.

Question 16

Which of the following is true about a catalyst in a chemical reaction?

Accepted Answer

A catalyst increases the rate of reaction by providing an alternative pathway with lower activation energy.

Question 17

Which of the following best describes the meaning of 'dynamic equilibrium' in a chemical system?

Accepted Answer

The forward and reverse reactions continue to occur at equal rates, so concentrations remain constant.

Question 18

A sample of gas has a density of $$1.96\ \mathrm{g/L} at$$ $$STP$$ ($$0\ ^\circ\mathrm{C}$$, $$1\ \mathrm{atm}). $$What is its molar mass?

Accepted Answer

$$M = 1.96\ \mathrm{g/L} 	imes 22.4\ \mathrm{L/mol} = 43.9\ \mathrm{g/mol}$$

Question 19

Which of the following best explains why the heat of vaporization ($$\Delta H_{vap}) is $$greater than the heat of fusion ($$\Delta H_{fus}) $$for a given substance?

Accepted Answer

It takes more energy to completely separate molecules from each other (liquid to gas) than to partially separate them (solid to liquid).

Question 20

Which of the following is the correct expression for the equilibrium constant $$K_c$$ for the reaction $$\mathrm{2NO}_2(g) \rightleftharpoons \mathrm{N}_2\mathrm{O}_4(g)$$?

Accepted Answer

$$K_c = \frac{[\mathrm{N}_2\mathrm{O}_4]}{[\mathrm{NO}_2]^2}$$

Thermochemistry, Gases, Liquids, Solutions, Kinetics, and Equilibrium: Mini-Study Guide

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