AP Chemistry: Thermodynamics — Practice Questions & Answers

Which of the following best describes an exothermic process?

• Energy is released to the surroundings and delta H is negative
• Energy is absorbed from the surroundings and delta H is positive
• No energy is exchanged with the surroundings
• The temperature of the surroundings decreases

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On a reaction energy (potential energy) diagram, an endothermic reaction is shown when the products are located:

• At a higher energy than the reactants
• At a lower energy than the reactants
• At the same energy as the reactants
• At the top of the activation energy barrier

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When two objects at different temperatures are placed in contact and reach thermal equilibrium, this means:

• Both objects are at the same temperature
• Both objects contain the same total thermal energy
• The hotter object stops losing energy but the cooler one keeps gaining it
• Heat continues to flow from the cold object to the hot object

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Which phase change is endothermic?

• Melting of solid ice into liquid water
• Freezing of liquid water into ice
• Condensation of water vapor into liquid
• Deposition of gas directly into a solid

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In the equation q = mc*deltaT, the symbol c represents:

• The specific heat capacity of the substance
• The total heat released by the reaction
• The mass of the substance
• The change in temperature

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The standard enthalpy of formation of any element in its most stable form, such as O2(g) or C(graphite), is equal to kJ/mol.

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Answer: 0 / zero

A 50.0 g sample of water (c = 4.18 J/(g*C)) is heated from 20.0 C to 60.0 C. How much heat is absorbed?

• 8360 J
• 4180 J
• 12540 J
• 2090 J

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Breaking chemical bonds and forming chemical bonds have which energy characteristics?

• Breaking bonds requires energy; forming bonds releases energy
• Breaking bonds releases energy; forming bonds requires energy
• Both breaking and forming bonds release energy
• Both breaking and forming bonds require energy

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A reaction has delta H = -92 kJ/mol. If the reaction is reversed, the enthalpy change of the reverse reaction is:

• +92 kJ/mol
• -92 kJ/mol
• -46 kJ/mol
• 0 kJ/mol

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A metal sample releases 500 J of heat as it cools by 25.0 C. If the metal has a mass of 40.0 g, what is its specific heat capacity?

• 0.500 J/(g*C)
• 2.00 J/(g*C)
• 0.250 J/(g*C)
• 1.25 J/(g*C)

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