Q: Which equation correctly expresses Hess's Law for calculating the enthalpy change of a reaction?

$$\Delta H_{\text{rxn}} = \sum n \Delta H_f^\circ(\text{products}) - \sum n \Delta H_f^\circ(\text{reactants})$$

Q: For the reaction $$2 O_3$(g) \rightarrow 3 O_2$(g)$$, which expression correctly relates the rate of disappearance of $$O_3 to $$the rate of appearance of $$O_2$$?

$$\text{Rate} = -\frac{1}{2} \frac{\Delta [O_3$]}{\Delta t} = \frac{1}{3} \frac{\Delta [O_2$]}{\Delta t}$$

Question 1

Which of the following statements best describes the relationship between enthalpy change ($$\Delta H) $$and heat ($$q) in a $$constant-pressure calorimetry experiment?

Accepted Answer

$$\Delta H = q at $$constant pressure.

Question 2

A reaction is carried out in a bomb calorimeter. Which of the following is true about the measurement obtained?

Accepted Answer

The measurement gives the change in internal energy $$\Delta E.$$

Question 3

Which equation correctly expresses Hess's Law for calculating the enthalpy change of a reaction?

Accepted Answer

$$\Delta H_{	ext{rxn}} = \sum n \Delta H_f^\circ(	ext{products}) - \sum n \Delta H_f^\circ(	ext{reactants})$$

Question 4

Which of the following is a correct statement about standard enthalpy of formation ($$\Delta H_f^\circ$$)?

Accepted Answer

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

Question 5

Given the reaction: $$\mathrm{C_3H_8(g) + 5 O_2$(g) \rightarrow 3 CO_2$(g) + 4 H_2O(l)}$$, and the following standard enthalpies of formation: $$\Delta H_f^\circ (CO_2$(g)) = -393.5 kJ/$$mol, $$\Delta H_f^\circ (H_2O(l)) = -285.8 kJ/$$mol, $$\Delta H_f^\circ (C_3H_8(g)) = -103.85 kJ/$$mol$$, what is $$\Delta H_{rxn}$?

Accepted Answer

$$-2219.9 kJ$$

Question 6

Which of the following best describes a catalyst's effect on a chemical reaction?

Accepted Answer

It lowers the activation energy, increasing the reaction rate.

Question 7

Which factor does NOT affect the rate of a chemical reaction?

Accepted Answer

The color of the reactants

Question 8

For the reaction $$2 O_3$(g) \rightarrow 3 O_2$(g)$$, which expression correctly relates the rate of disappearance of $$O_3 to $$the rate of appearance of $$O_2$$?

Accepted Answer

$$	ext{Rate} = -\frac{1}{2} \frac{\Delta [O_3$]}{\Delta t} = \frac{1}{3} \frac{\Delta [O_2$]}{\Delta t}$$

Question 9

Which of the following is true about bond enthalpy?

Accepted Answer

Bond enthalpy is always positive because energy is required to break bonds.

Question 10

A reaction is found to be first order in $$A$$ and second order in $$B. $$Which is the correct rate law?

Accepted Answer

$$	ext{Rate} = k[A][B]^2$$

Question 11

Which of the following best explains why increasing temperature generally increases the rate of a chemical reaction?

Accepted Answer

It increases the kinetic energy of molecules, leading to more frequent and energetic collisions.

Question 12

Which of the following is the correct unit for the rate constant $$k$$ for a second-order reaction?

Accepted Answer

$$\mathrm{M}^{-1} \mathrm{s}^{-1}$$

Question 13

Which of the following is true about the rate law for a reaction?

Accepted Answer

It must be determined experimentally.

Question 14

Which of the following best describes the effect of increasing the surface area of a solid reactant?

Accepted Answer

It increases the reaction rate by increasing the number of effective collisions.

Question 15

Which of the following is the correct integrated rate law for a first-order reaction?

Accepted Answer

$$\ln [A]_t = -kt + \ln [A]_0$$

Question 16

Which of the following is true about the half-life of a first-order reaction?

Accepted Answer

It is independent of the initial concentration.

Question 17

Which of the following best describes the difference between thermodynamics and kinetics?

Accepted Answer

Thermodynamics tells you the energy change and equilibrium, while kinetics tells you the reaction pathway and speed.

Finishing Enthalpy and Introduction to Chemical Kinetics: Study Notes

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