Q: Which of the following is the correct expression for the standard enthalpy change of a reaction ($$\Delta H^\circ_{rxn}$$)?

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

Q: Which equation is used to calculate the heat required to raise the temperature of a substance?

$$q = m \times c \times \Delta T$$

Question 1

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

Accepted Answer

Energy cannot be created or destroyed, only transferred or transformed.

Question 2

A chemical reaction occurs in a closed container and releases heat to the surroundings. Which term best describes this process?

Accepted Answer

Exothermic

Question 3

Which equation correctly relates the change in internal energy ($$\Delta U) to $$heat ($$q) $$and work ($$w$$)?

Accepted Answer

$$\Delta U = q + w$$

Question 4

If a system absorbs 150 J of heat and does 40 J of work on the surroundings, what is the change in internal energy ($$\Delta U$$)?

Accepted Answer

$$\Delta U = 110 	ext{ J}$$

Question 5

Which of the following best describes the sign convention for work ($$w) in $$thermodynamics?

Accepted Answer

Work done on the system by the surroundings is positive.

Question 6

Which of the following is the correct expression for the standard enthalpy change of a reaction ($$\Delta H^\circ_{rxn}$$)?

Accepted Answer

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

Question 7

A reaction has $$\Delta H = -200 	ext{ kJ}$$ and $$\Delta S = -0.5 	ext{ kJ/K}. At $$what temperature does the reaction become non-spontaneous?

Accepted Answer

$$T = 400 	ext{ K}$$

Question 8

Which of the following processes is always endothermic?

Accepted Answer

Melting of ice

Question 9

Which equation is used to calculate the heat required to raise the temperature of a substance?

Accepted Answer

$$q = m 	imes c 	imes \Delta T$$

Question 10

A 50 g sample of water is heated from 20°C to 70°C. If the specific heat capacity of water is $$4.18 	ext{ J/g} \cdot 	ext{K}$$, how much heat is absorbed?

Accepted Answer

$$q = 10,450 	ext{ J}$$

Question 11

Which of the following statements about entropy ($$S) is $$correct?

Accepted Answer

Entropy is a measure of the disorder or randomness of a system.

Question 12

Which of the following reactions is most likely to have a positive entropy change ($$\Delta S$$)?

Accepted Answer

Dissolution of NaCl in water

Question 13

Which formula is used to determine the spontaneity of a process at constant temperature and pressure?

Accepted Answer

$$\Delta G = \Delta H - T \Delta S$$

Question 14

A reaction has $$\Delta H = 100 	ext{ kJ}$$ and $$\Delta S = 0.25 	ext{ kJ/K}. At$$ $$T = 400 	ext{ K}$$, what is $$\Delta G$$?

Accepted Answer

$$\Delta G = 0 	ext{ kJ}$$

Question 15

Which of the following best describes a spontaneous process?

Accepted Answer

A process that occurs without outside intervention.

Question 16

Which statement about the enthalpy of formation ($$\Delta H^\circ_f) is $$correct?

Accepted Answer

It is the enthalpy change for forming 1 mole of a compound from its elements in their standard states.

Question 17

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 18

A student mixes two solutions in a coffee-cup calorimeter and measures a temperature increase. What does this indicate about the reaction?

Accepted Answer

The reaction is exothermic.

Question 19

Which of the following factors will increase the spontaneity of a process?

Accepted Answer

A negative $$\Delta H$$ and a positive $$\Delta S$$

Question 20

Which of the following best explains why the dissolution of ammonium nitrate in water is spontaneous, even though it absorbs heat?

Accepted Answer

The increase in entropy ($$\Delta S) $$outweighs the positive enthalpy change ($$\Delta H).$$

Thermodynamics and Energy in General Chemistry: Key Concepts and Applications

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