Q: In a coffee cup calorimeter experiment, 29.78 g of magnesium ribbon (Mg, $$C = 1.04 J/g$$°C) is added to 100.0 g of water at 30.0°C. After reaction, the temperature is 39.0°C. What is the heat absorbed by the water?

$$q = 100.0 \times 4.184 \times (39.0 - 30.0) = 3,765.6 J$$

Q: Which of the following is the correct formula for calculating the enthalpy change of a reaction using standard enthalpies of formation?

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

Question 1

Which of the following best describes a state function in thermodynamics?

Accepted Answer

A property that depends only on the initial and final states of a system, not on the path taken.

Question 2

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

Accepted Answer

$$\Delta E = q + w$$

Question 3

A bomb calorimeter is used to measure the energy released during the combustion of a sample at constant volume. Which thermodynamic quantity does it directly measure?

Accepted Answer

Change in internal energy ($$\Delta E)$$

Question 4

Which of the following is NOT a correct statement about specific heat capacity ($$C$$)?

Accepted Answer

It is always negative for exothermic reactions.

Question 5

Which formula is used to calculate the amount of heat ($$q) $$absorbed or released by a substance?

Accepted Answer

$$q = m C \Delta T$$

Question 6

In a coffee cup calorimeter experiment, 29.78 g of magnesium ribbon (Mg, $$C = 1.04 J/g$$°C) is added to 100.0 g of water at 30.0°C. After reaction, the temperature is 39.0°C. What is the heat absorbed by the water?

Accepted Answer

$$q = 100.0 	imes 4.184 	imes (39.0 - 30.0) = 3,765.6 J$$

Question 7

Which of the following best describes the difference between kinetic and potential energy?

Accepted Answer

Kinetic energy is the energy of motion, while potential energy is stored energy due to position or composition.

Question 8

Which of the following reactions would produce significant work due to a change in volume ($$\Delta V) $$under constant pressure?

Accepted Answer

Zn (s) + 2 HCl (aq) $$\rightarrow$$ ZnCl$$_2 (aq) + H$_2 (g)$$

Question 9

Which equation is used to calculate the work ($$w) $$done by a system at constant pressure?

Accepted Answer

$$w = -P \Delta V$$

Question 10

Which statement about enthalpy ($$\Delta H) is $$correct?

Accepted Answer

At constant pressure, the change in enthalpy equals the heat exchanged: $$\Delta H = q_p$$

Question 11

Which of the following is the correct formula for calculating the enthalpy change of a reaction using standard enthalpies of formation?

Accepted Answer

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

Question 12

Which of the following is a correct application of Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the sum of the enthalpy changes for each step, regardless of the path taken.

Question 13

Which of the following best explains why the theoretical NaCl$$_2$$ unit cannot exist in real life?

Accepted Answer

The energy required to remove two electrons from Na is much greater than the lattice energy gained, making the process energetically unfavorable.

Question 14

Which of the following statements about bond enthalpy is correct?

Accepted Answer

Bond enthalpy is the energy required to break one mole of a specific bond in the gas phase.

Question 15

Given the following average bond enthalpies: C-H = 413 kJ/mol, O-H = 463 kJ/mol, C=O = 799 kJ/mol, calculate the enthalpy change for the reaction: CH$$_4 (g) + 2 O$_2 (g$$) $$\rightarrow CO$_2 (g) + 2 H$_2O (g).$$

Accepted Answer

$$\Delta H = [4 	imes 413 + 2 	imes 799] - [4 	imes 463 + 2 	imes 799] = -200 kJ/$$mol

Question 16

Which of the following is NOT a state function?

Accepted Answer

Work ($$w)$$

Question 17

A student mixes 50.0 mL of 0.400 M NaCl solution with 50.0 mL of 0.200 M AgNO$$_3$$ solution in a calorimeter. The temperature rises by 2.10°C. If the specific heat of the solution is 4.18 J/g°C and the total mass is 100.0 g, what is the heat released?

Accepted Answer

$$q = 100.0 	imes 4.18 	imes 2.10 = 877.8 J$$

Question 18

Which of the following is the correct definition of the standard enthalpy of formation ($$\Delta H^\circ_f) $$for a compound?

Accepted Answer

The enthalpy change when one mole of a compound is formed from its elements in their standard states.

Thermochemistry and Calorimetry: Study Notes for General Chemistry

Guida di studio - Domande di pratica

Study guide - Flashcard