Q: A 2.49 g sample of aniline ($$\mathrm{C_6H_5NH_2}$$, molar mass = 93.13 g/mol) is combusted in a bomb calorimeter with a heat capacity of $$4.25\ \mathrm{kJ$$/^{\circ}$$C}. $$The temperature rises from $$29.5^{\circ}C$ to 69.8$$^{\circ}$$C. $$What is the standard enthalpy of combustion $$\Delta H$$^{\circ}$$_{\mathrm{comb}}$$ for aniline in $$\mathrm{kJ/mol}$$?

$$\Delta H$$^{\circ}$$_{\mathrm{comb}} = -1.71 \times 10^3$\ \mathrm{kJ/mol}$$

Q: Given the following initial rate data for the reaction $$\mathrm{NO_2$(g)} + \mathrm{O_3$(g)} \rightarrow \mathrm{NO_3$(g)} + \mathrm{O_2$(g)}$$: $$[\mathrm{NO_2$}]_i = 0.10\ \mathrm{M},\ [\mathrm{O_3$}]_i = 0.33\ \mathrm{M},\ \text{Rate} = 1.42\ \mathrm{M/s}$$ $$[\mathrm{NO_2$}]_i = 0.10\ \mathrm{M},\ [\mathrm{O_3$}]_i = 0.66\ \mathrm{M},\ \text{Rate} = 2.84\ \mathrm{M/s}$$ $$[\mathrm{NO_2$}]_i = 0.25\ \mathrm{M},\ [\mathrm{O_3$}]_i = 0.66\ \mathrm{M},\ \text{Rate} = 7.10\ \mathrm{M/s}$$ What is the rate law and value of $$k$$?

$$\text{Rate} = [43\ \mathrm{M$$^{-1}$$s^{-1}$$}][\mathrm{$$NO_2$$}][\mathrm{$$O_3$$}]$

Question 1

Which of the following statements about the law of conservation of energy is FALSE?

Accepted Answer

Energy cannot be transferred from one object to another.

Question 2

A chemical system absorbs 50.0 kJ of heat from the surroundings and does 15.0 kJ of work on the surroundings. What is the change in internal energy $$\Delta E of $$the system?

Accepted Answer

$$\Delta E = +35.0\ \mathrm{kJ}$$

Question 3

Which of the following sign conventions for $$q ($$heat) and $$w ($$work) represents a system that is losing heat to the surroundings and having work done on it by the surroundings?

Accepted Answer

$$q = -,\ w = +$$

Question 4

A gas expands from 5.00 L to 15.00 L against a constant external pressure of 2.00 atm, while absorbing 300 J of heat. What is the change in internal energy $$\Delta E$$? (Use $$1\ \mathrm{L \cdot atm} = 101.3\ \mathrm{J})$$

Accepted Answer

$$\Delta E = -624\ \mathrm{J}$$

Question 5

A 2.49 g sample of aniline ($$\mathrm{C_6H_5NH_2}$$, molar mass = 93.13 g/mol) is combusted in a bomb calorimeter with a heat capacity of $$4.25\ \mathrm{kJ$$/^{\circ}$$C}. $$The temperature rises from $$29.5^{\circ}C$ to 69.8$$^{\circ}$$C. $$What is the standard enthalpy of combustion $$\Delta H$$^{\circ}$$_{\mathrm{comb}}$$ for aniline in $$\mathrm{kJ/mol}$$?

Accepted Answer

$$\Delta H$$^{\circ}$$_{\mathrm{comb}} = -1.71 	imes 10^3$\ \mathrm{kJ/mol}$$

Question 6

Consider a reaction with $$\Delta H \u003e 0$$ and $$\Delta S \u003e 0. $$Which statement is TRUE about its spontaneity?

Accepted Answer

The reaction is spontaneous only at high temperatures.

Question 7

For the reaction $$2\ \mathrm{H_2S(g)} + 3\ \mathrm{O_2$(g)} \rightarrow 2\ \mathrm{SO_2$(g)} + 2\ \mathrm{H_2O(g)}$$ with $$\Delta H = -1036\ \mathrm{kJ}$$ and $$\Delta S = -153.2\ \mathrm{J/K}$$, above what temperature does the reaction become nonspontaneous?

Accepted Answer

$$T = 6762\ \mathrm{K}$$

Question 8

Given the following reactions and their standard free energy changes:

$$2\ \mathrm{O_3$(g)} \rightarrow 3\ \mathrm{O_2$(g)}\ \ \Delta G$$^{\circ}$$ = +489.6\ \mathrm{kJ}$$

$$\mathrm{O_2$(g)} \rightarrow 2\ \mathrm{O(g)}\ \ \Delta G$$^{\circ}$$ = +463.4\ \mathrm{kJ}$$

$$\mathrm{NO(g)} + \mathrm{O_3$(g)} \rightarrow \mathrm{NO_2$(g)} + \mathrm{O_2$(g)}\ \ \Delta G$$^{\circ}$$ = -199.5\ \mathrm{kJ}$$

Calculate $$\Delta G$$^{\circ}$$ for $$\mathrm{NO(g)} + \mathrm{O(g)} \rightarrow \mathrm{$$NO_2(g$$)}$$.

Accepted Answer

$$\Delta G$$^{\circ}$$ = +277.0\ \mathrm{kJ}$$

Question 9

For the reaction $$2\ \mathrm{Hg(g)} + \mathrm{O_2$(g)} \rightarrow 2\ \mathrm{HgO(s)}$$ with $$\Delta G$$^{\circ}$$ = -180.8\ \mathrm{kJ} at$$ $$298\ \mathrm{K}$$, and partial pressures $$P_{\mathrm{Hg}} = 0.025\ \mathrm{atm}$$, $$P_{\mathrm{O_2$}} = 0.037\ \mathrm{atm}$$, what is $$\Delta G_{\mathrm{rxn}} at $$these conditions? ($$R = 8.314\ \mathrm{J/(mol\cdot K)})$$

Accepted Answer

$$\Delta G_{\mathrm{rxn}} = -154.4\ \mathrm{kJ}$$

Question 10

Which of the following balanced reactions corresponds to the rate relationship $$	ext{Rate} = -\frac{1}{2} \frac{d[\mathrm{N_2O}]}{dt} = \frac{d[\mathrm{N_2$}]}{dt} = \frac{1}{2} \frac{d[\mathrm{O_2$}]}{dt}$$?

Accepted Answer

$$2\ \mathrm{N_2O} \rightarrow 2\ \mathrm{N_2$} + \mathrm{O_2$}$$

Question 11

Given the following initial rate data for the reaction $$\mathrm{NO_2$(g)} + \mathrm{O_3$(g)} ightarrow \mathrm{NO_3$(g)} + \mathrm{O_2$(g)}$$:

$$[\mathrm{NO_2$}]_i = 0.10\ \mathrm{M},\ [\mathrm{O_3$}]_i = 0.33\ \mathrm{M},\ 	ext{Rate} = 1.42\ \mathrm{M/s}$$

$$[\mathrm{NO_2$}]_i = 0.10\ \mathrm{M},\ [\mathrm{O_3$}]_i = 0.66\ \mathrm{M},\ 	ext{Rate} = 2.84\ \mathrm{M/s}$$

$$[\mathrm{NO_2$}]_i = 0.25\ \mathrm{M},\ [\mathrm{O_3$}]_i = 0.66\ \mathrm{M},\ 	ext{Rate} = 7.10\ \mathrm{M/s}$$

What is the rate law and value of $$k$$?

Accepted Answer

$$	ext{Rate} = [43\ \mathrm{M$$^{-1}$$s^{-1}$$}][\mathrm{$$NO_2$$}][\mathrm{$$O_3$$}]$

Question 12

A reaction has $$\Delta H = +85\ \mathrm{kJ}$$ and $$\Delta S = +200\ \mathrm{J/K}. At $$what temperature (in $$\mathrm{K}) $$does the reaction become spontaneous?

Accepted Answer

$$T = 425\ \mathrm{K}$$

Question 13

Which of the following best describes a process that is exothermic and increases the entropy of the system?

Accepted Answer

Combustion of methane: $$\mathrm{CH_4$(g) + 2\ O_2$(g) \rightarrow CO_2$(g) + 2\ H_2O(g)}$$

Question 14

A reaction at $$25^{\circ}C$ has $$\Delta $$G^{\circ} = +10.0$$\ \mathrm{kJ}$$. If the reaction quotient Q$ is 0.001$, what is $$\Delta G$$ at these conditions? (R = 8.314$$\ \mathrm{J/(mol\cdot K)}$$)

Accepted Answer

$$\Delta G = +4.1\ \mathrm{kJ}$$

Question 15

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

Accepted Answer

The enthalpy change for a reaction is the same, regardless of the number of steps in the reaction pathway.

Question 16

A reaction is found to be spontaneous at room temperature but becomes nonspontaneous at higher temperatures. Which combination of $$\Delta H$$ and $$\Delta S is $$consistent with this behavior?

Accepted Answer

$$\Delta H \u003c 0$$, $$\Delta S \u003c 0$$

Question 17

Which of the following scenarios best illustrates the concept of energy transfer between a system and its surroundings?

Accepted Answer

A hot metal block placed in cool water, causing the water temperature to rise.

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