Q: Aluminum metal has a specific heat of $0.900~\mathrm{J}/\mathrm{g}^\circ\mathrm{C}$. Calculate the amount of heat required to raise the temperature of 10.5 moles of Al from 30.5°C to 225°C.

$q = 5.33 \times 10^4~\mathrm{J}$

Question 1

A container fitted with a movable piston at constant atmospheric pressure contains the reaction: $2 \mathrm{C}_2\mathrm{H}_6(l) + 7 \mathrm{O}_2(g) \rightarrow 4 \mathrm{CO}_2(g) + 6 \mathrm{H}_2\mathrm{O}(g)$. What happens to the volume and work during this reaction?

Accepted Answer

Volume will increase and work will be done by the system.

Question 2

Calculate the amount of work done, in joules, when 2.5 mol of $\mathrm{H}_2\mathrm{O}$ vaporizes at 1.0 atm and 25°C. Assume the volume of liquid $\mathrm{H}_2\mathrm{O}$ is negligible compared to that of vapor. ($1 \mathrm{~L~atm} = 101.3~\mathrm{J}$)

Accepted Answer

$w = -6,200~\mathrm{J}$

Question 3

A gas expands from 15 L to 35 L against a constant external pressure of 1.5 atm. Calculate the work energy, $w$, gained or lost by the system. ($1~\mathrm{L~atm} = 101~\mathrm{J}$)

Accepted Answer

$w = -3,030~\mathrm{J}$

Question 4

For a particular process carried out at constant pressure, $q = 125~\mathrm{kJ}$ and $w = -15~\mathrm{kJ}$. Therefore, $\Delta E = ?$ and $\Delta H = ?$

Accepted Answer

$\Delta E = 110~\mathrm{kJ}$, $\Delta H = 125~\mathrm{kJ}$

Question 5

A gas is allowed to expand, at constant temperature, from a volume of 1.0 L to 10.1 L against an external pressure of 0.50 atm. If the gas absorbs 250 J of heat from the surroundings, what are the values of $q$, $w$, and $\Delta E$? ($1~\mathrm{L~atm} = 101.3~\mathrm{J}$)

Accepted Answer

$q = 250~\mathrm{J}$, $w = -460~\mathrm{J}$, $\Delta E = -210~\mathrm{J}$

Question 6

When 2.000 moles of $\mathrm{H}_2(g)$ reacts with 1.000 mol of $\mathrm{O}_2(g)$ to form 2.000 mol of $\mathrm{H}_2\mathrm{O}(l)$ at 25°C and a constant pressure of 1.00 atm, 136.6 kJ of heat are released during this reaction, and $P\Delta V$ is equal to $-7.400~\mathrm{kJ}$. What are $\Delta H$ and $\Delta E$?

Accepted Answer

$\Delta H = -136.6~\mathrm{kJ}$, $\Delta E = -129.2~\mathrm{kJ}$

Question 7

Aluminum metal has a specific heat of $0.900~\mathrm{J}/\mathrm{g}^\circ\mathrm{C}$. Calculate the amount of heat required to raise the temperature of 10.5 moles of Al from 30.5°C to 225°C.

Accepted Answer

$q = 5.33 	imes 10^4~\mathrm{J}$

Question 8

Three separate 3.5 g blocks of Al, Cu, and Fe at 25°C each absorb 0.505 kJ of heat. Which block reaches the highest temperature? The specific heats of Al, Cu, and Fe are $0.900~\mathrm{J}/\mathrm{g}^\circ\mathrm{C}$, $0.385~\mathrm{J}/\mathrm{g}^\circ\mathrm{C}$, and $0.444~\mathrm{J}/\mathrm{g}^\circ\mathrm{C}$, respectively.

Accepted Answer

Copper (Cu)

Question 9

A beaker contains 115 g of ethanol at 18.2°C. If the ethanol absorbs 1125 J of heat without losing heat to the surroundings, what will be the final temperature of the ethanol? The specific heat of ethanol is $2.46~\mathrm{J}/\mathrm{g}^\circ\mathrm{C}$.

Accepted Answer

$T_{final} = 21.4^\circ\mathrm{C}$

Question 10

The specific heat of gold is $0.129~\mathrm{J}/\mathrm{g}^\circ\mathrm{C}$. What is the molar heat capacity of gold?

Accepted Answer

$C_{molar} = 25.1~\mathrm{J}/\mathrm{mol}^\circ\mathrm{C}$

Question 11

10.1 g CaO is dropped into a styrofoam coffee cup containing 157 g $\mathrm{H}_2\mathrm{O}$ at 18.0°C. If the following reaction occurs, what temperature will the water reach, assuming the cup is a perfect insulator and absorbs only a negligible amount of heat? (The specific heat of water is $4.18~\mathrm{J}/\mathrm{g}^\circ\mathrm{C}$) $\mathrm{CaO}(s) + \mathrm{H}_2\mathrm{O}(l) \rightarrow \mathrm{Ca(OH)}_2(s)$ $\Delta H_{rxn} = -6.48~\mathrm{kJ}/\mathrm{mol}$

Accepted Answer

$T_{final} = 23.6^\circ\mathrm{C}$

Question 12

A sample of benzoic acid is burned in a calorimeter containing 1,000 g of water, and a temperature rise of 4.21°C was observed. What is the heat capacity of the bomb calorimeter excluding the water?

Accepted Answer

$C_{cal} = 1,260~\mathrm{J}/^\circ\mathrm{C}$

Question 13

Concerning the reaction $\mathrm{C(graphite)} + \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g)$, $\Delta H = -393~\mathrm{kJ}/\mathrm{mol}$, how many grams of graphite must be burned to release 275 kJ of heat?

Accepted Answer

8.39 g

Question 14

Find $\Delta H$ for $\mathrm{C}_3\mathrm{H}_8(g) + 6 \mathrm{H}_2\mathrm{O}(g) \rightarrow 3 \mathrm{CO}_2(g) + 10 \mathrm{H}_2(g)$ given $\mathrm{C}_3\mathrm{H}_8(g) + 3 \mathrm{H}_2\mathrm{O}(g) \rightarrow 3 \mathrm{CO}(g) + 7 \mathrm{H}_2(g)$ $\Delta H = 499~\mathrm{kJ}$ and $\mathrm{CO}(g) + \mathrm{H}_2\mathrm{O}(g) \rightarrow \mathrm{CO}_2(g) + \mathrm{H}_2(g)$ $\Delta H = 41~\mathrm{kJ}$.

Accepted Answer

$622~\mathrm{kJ}$

Question 15

Which of the following processes is endothermic, given the following: $\mathrm{S}(s) + \frac{1}{2} \mathrm{O}_2(g) \rightarrow \mathrm{SO}_2(g)$ $\Delta H = -299~\mathrm{kJ}/\mathrm{mol}$, $\mathrm{S}(s) + 3/2 \mathrm{O}_2(g) \rightarrow \mathrm{SO}_3(g)$ $\Delta H = -395~\mathrm{kJ}/\mathrm{mol}$

Accepted Answer

$\mathrm{SO}_3(g) \rightarrow \mathrm{SO}_2(g) + \frac{1}{2} \mathrm{O}_2(g)$

Question 16

Which of the following processes is exothermic, given the following: $2 \mathrm{N}_2(g) + 2 \mathrm{O}_2(g) \rightarrow 2 \mathrm{N}_2\mathrm{O}_4(l)$ $\Delta H = -67.1~\mathrm{kJ}/\mathrm{mol}$, $2 \mathrm{N}_2\mathrm{O}_4(l) \rightarrow 2 \mathrm{NO}_2(g)$ $\Delta H = 67.0~\mathrm{kJ}/\mathrm{mol}$

Accepted Answer

$2 \mathrm{N}_2(g) + 2 \mathrm{O}_2(g) \rightarrow 2 \mathrm{N}_2\mathrm{O}_4(l)$

Question 17

Which reaction represents the standard enthalpy of formation for sucrose ($\mathrm{C}_{12}\mathrm{H}_{22}\mathrm{O}_{11}$)?

Accepted Answer

$12 \mathrm{C}(graphite) + 11 \mathrm{H}_2(g) + 11 \mathrm{O}_2(g) \rightarrow \mathrm{C}_{12}\mathrm{H}_{22}\mathrm{O}_{11}(s)$

Question 18

Which of the following has a $\Delta H_f^\circ = 0~\mathrm{kJ}/\mathrm{mol}$?

Accepted Answer

$\mathrm{O}_2(g)$

Question 19

Use the given standard enthalpies of formation to calculate $\Delta H^\circ$ for the following reaction: $3 \mathrm{Fe}_2\mathrm{O}_3(s) + \mathrm{CO}(g) \rightarrow 2 \mathrm{Fe}_3\mathrm{O}_4(s) + \mathrm{CO}_2(g)$, given $\Delta H_f^\circ$ values: $\mathrm{Fe}_2\mathrm{O}_3(s): -824.2~\mathrm{kJ}/\mathrm{mol}$, $\mathrm{Fe}_3\mathrm{O}_4(s): -1118.4~\mathrm{kJ}/\mathrm{mol}$, $\mathrm{CO}(g): -110.5~\mathrm{kJ}/\mathrm{mol}$, $\mathrm{CO}_2(g): -393.5~\mathrm{kJ}/\mathrm{mol}$.

Accepted Answer

$\Delta H^\circ = -481.8~\mathrm{kJ}$

Question 20

Ethanol undergoes combustion in oxygen to produce carbon dioxide gas and liquid water. The standard heat of combustion of ethanol, $\mathrm{C}_2\mathrm{H}_5\mathrm{OH}(l)$, is $-1366.8~\mathrm{kJ}/\mathrm{mol}$. Given that $\Delta H_f^\circ(\mathrm{CO}_2(g)) = -393.5~\mathrm{kJ}/\mathrm{mol}$ and $\Delta H_f^\circ(\mathrm{H}_2\mathrm{O}(l)) = -285.8~\mathrm{kJ}/\mathrm{mol}$, what is the standard enthalpy of formation of ethanol?

Accepted Answer

$-277.0~\mathrm{kJ}/\mathrm{mol}$

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