Q: Which of the following best describes the sign conventions for $q$, $w$, and $\Delta U$ in the first law of thermodynamics for a system that absorbs heat and does work on the surroundings?

$q > 0$, $w < 0$, $\Delta U$ can be positive or negative

Q: Which of the following is the correct expression for the work done by a gas during an isothermal, reversible expansion from volume $V_1$ to $V_2$ at temperature $T$?

$w = -nRT \ln \left( \frac{V_2}{V_1} \right)$

Q: If the enthalpy of formation $\Delta H_f^\circ$ of a compound is negative, what does this indicate about the formation of the compound from its elements in their standard states?

The reaction is exothermic and releases heat.

Question 1

A piston containing two moles of an ideal gas expands to twice its volume against an external pressure of 2.0 atm from an initial volume of 1.0 L. Simultaneously, the temperature of the chamber is raised from 25 $^\circ$C to 50 $^\circ$C. Calculate the work $w$, heat $q$, and change in internal energy $\Delta U$ for the system. (Assume $R = 0.0821$ L·atm·mol$^{-1}$·K$^{-1}$ and ideal gas behavior.)

Accepted Answer

$w = -2.0$ L·atm, $q = 3.3$ L·atm, $\Delta U = 1.3$ L·atm

Question 2

Suppose 72.0 g of hot metal, which is initially at 190.0 $^\circ$C, is plunged into 110.0 g of water that is initially at 40.0 $^\circ$C. The metal cools down and the water heats up until they reach a common temperature of 60.0 $^\circ$C. Calculate the specific heat capacity of the metal, using $4.184$ J·g$^{-1}$·K$^{-1}$ as the specific heat capacity of water.

Accepted Answer

$c_{metal} = 0.42$ J·g$^{-1}$·K$^{-1}$

Question 3

The salt cesium sulfate dissolves in water according to the reaction:

$\mathrm{Cs_2SO_4(s) \rightarrow 2Cs^+(aq) + SO_4^{2-}(aq)}$

Given: $\Delta H_f^\circ(\mathrm{Cs_2SO_4(s)}) = -1443.0$ kJ/mol, $\Delta H_f^\circ(\mathrm{Cs^+ (aq)}) = -252.8$ kJ/mol, $\Delta H_f^\circ(\mathrm{SO_4^{2-} (aq)}) = -909.3$ kJ/mol. Calculate the standard enthalpy change $\Delta H$ for this reaction.

Accepted Answer

$\Delta H = +28.1$ kJ

Question 4

When 3.35 g of ammonium perchlorate ($\mathrm{NH_4ClO_4}$) is dissolved in 105 g of water in a Styrofoam calorimeter of negligible heat capacity, the temperature drops from 25.00 $^\circ$C to 22.74 $^\circ$C. Based on this observation, calculate $q$ for the water and $\Delta H$ for the process. The specific heat of water is $4.184$ J·g$^{-1}$·K$^{-1}$.

Accepted Answer

$q = -990$ J, \Delta H = +1.1$ kJ

Question 5

Use Hess's Law to determine $\Delta H$ for the following target reaction:

$\mathrm{N_2 (g) + 1/2 O_2 (g) + Cl_2 (g) \rightarrow 2 NOCl (g)}$

Given:
$\mathrm{N_2 (g) + O_2 (g) \rightarrow 2 NO (g)}$ $\Delta H = 180.5$ kJ
$\mathrm{NO (g) + 1/2 Cl_2 (g) \rightarrow NOCl (g)}$ $\Delta H = -38.6$ kJ

Accepted Answer

$\Delta H = 103.3$ kJ

Question 6

A sample of gas occupies 5.00 L at 27 $^\circ$C and 1.00 atm. What will be its volume at 127 $^\circ$C and 2.00 atm, assuming ideal gas behavior?

Accepted Answer

3.33 L

Question 7

Which of the following statements best explains why the temperature of water decreases when ammonium perchlorate dissolves in it?

Accepted Answer

The dissolution is endothermic, so heat is absorbed from the water.

Question 8

Which of the following best describes the sign conventions for $q$, $w$, and $\Delta U$ in the first law of thermodynamics for a system that absorbs heat and does work on the surroundings?

Accepted Answer

$q > 0$, $w < 0$, $\Delta U$ can be positive or negative

Question 9

A 50.0 g sample of metal at 150.0 $^\circ$C is placed in 100.0 g of water at 25.0 $^\circ$C. The final temperature is 30.0 $^\circ$C. What is the specific heat capacity of the metal? (Assume $c_{water} = 4.184$ J·g$^{-1}$·K$^{-1}$.)

Accepted Answer

0.21 J·g$^{-1}$·K$^{-1}$

Question 10

Which of the following is the correct expression for the work done by a gas during an isothermal, reversible expansion from volume $V_1$ to $V_2$ at temperature $T$?

Accepted Answer

$w = -nRT \ln \left( \frac{V_2}{V_1} \right)$

Question 11

If the enthalpy of formation $\Delta H_f^\circ$ of a compound is negative, what does this indicate about the formation of the compound from its elements in their standard states?

Accepted Answer

The reaction is exothermic and releases heat.

Question 12

A chemical reaction has $\Delta H = +50$ kJ and $\Delta S = +100$ J·K$^{-1}$. At what temperature (in K) does the reaction become spontaneous?

Accepted Answer

T > 500 K

Question 13

Which of the following best describes the process of calorimetry?

Accepted Answer

Measuring the amount of heat absorbed or released during a chemical or physical process.

Question 14

Which of the following is true for an endothermic reaction?

Accepted Answer

$\Delta H > 0$ and the system absorbs heat from the surroundings.

Question 15

A reaction vessel contains 1.00 mol of an ideal gas at 1.00 atm and 273 K. If the gas is compressed isothermally to 0.50 L, what is the final pressure?

Accepted Answer

2.00 atm

Quiz 7

Study Guide - Practice Questions

Study Guide - Flashcards