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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