Chapter 15

How many joules are absorbed in a process that absorbs 0.5720 kcal?

Transportation Ethanol is being used as an additive to gasoline. The combustion of 1 mol of ethanol releases 1367 kJ of energy. How many Calories are released?

To vaporize 2.00 g of ammonia, 656 calories are required. How many kilojoules are required to vaporize the same mass of ammonia?

The combustion of one mole of ethanol releases 326.7 Calories of energy. How many kilojoules are released?

Metallurgy A 25.0-g bolt made of an alloy absorbed 250 J of heat as its temperature changed from 25.0°C to 78.0°C. What is the specific heat of the alloy?

Why is a foam cup used in a student calorimeter rather than a typical glass beaker?

Give two examples of chemical systems and define the universe in terms of those examples.

Under what condition is the heat (q) evolved or absorbed in a chemical reaction equal to a change in enthalpy (?H)?

The enthalpy change for a reaction, ?H, is negative. What does this indicate about the chemical potential energy of the system before and after the reaction?

What is the sign of ?H for an exothermic reaction? An endothermic reaction?

How many joules of heat are lost by 3580 kg of granite as it cools from 41.2°C to -12.9°C? The specific heat of granite is 0.803 J/(g·°C).

Swimming Pool A swimming pool measuring 20.0 m × 12.5 m is filled with water to a depth of 3.75 m. If the initial temperature is 18.4°C, how much heat must be added to the water to raise its temperature to 29.0°C? Assume that the density of water is 1.000 g/mL.

Food Preparation When 10.2 g of canola oil at 25.0°C is placed in a wok, 3.34 kJ of heat is required to heat it to a temperature of 196.4°C. What is the specific heat of the canola oil?

Alloys When a 58.8-g piece of hot alloy is placed in 125 g of cold water in a calorimeter, the temperature of the alloy decreases by 106.1°C, while the temperature of the water increases by 10.5°C. What is the specific heat of the alloy?

Write the sign of \(\Delta H_{ \text { sytem for each of the following }}\) changes in physical state. a. \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\mathrm{s}) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(1)\) b. \(\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightarrow \mathrm{H}_{2} \mathrm{O}(1)\) \(\mathrm{c} . \mathrm{CH}_{3} \mathrm{OH}(1) \rightarrow \mathrm{CH}_{3} \mathrm{OH}(\mathrm{g})\) \(\mathrm{d} . \mathrm{NH}_{3}(1) \rightarrow \mathrm{NH}_{3}(\mathrm{s})\)

The molar enthalpy of fusion of methanol is 3.22 \({kJ} / {mol}\) . What does this mean?

Explain how perspiration can help cool your body.

Grilling What mass of propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\) must be burned in a barbecue grill to release 4560 \(\mathrm{kJ}\) of heat? The \(\Delta H_{\mathrm{comb}}\) of propane is \(-2219 \mathrm{k} / \mathrm{mol} .\)

For a given compound, what does the standard enthalpy of formation describe?

How does ?H for a thermochemical equation change when the amounts of all substances are tripled and the equation is reversed?

Use standard enthalpies of formation from Table \(R-11\) on page 975 to calculate \(\Delta H_{\text { ran for the following }}^{\circ}\) reaction. \(\mathrm{P}_{4} \mathrm{O}_{6}(\mathrm{s})+2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{P}_{4} \mathrm{O}_{10}(\mathrm{s})\)

Use Hess's law and the following thermochemical equations to produce the thermochemical equation for the reaction \(\mathrm{C}(\mathrm{s}, \text { diamond }) \rightarrow \mathrm{C}(\mathrm{s}, \text { graphite).What is }\) \(\Delta H\) for the reaction? a. \(C(s, \text { graphite })+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g) \quad \Delta H=-394 \mathrm{kJ}\) b. \(C(s, \text { diamond })+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g) \quad \Delta H=-396 \mathrm{kJ}\)

Use Hess’s law and the changes in enthalpy for the following two generic reactions to calculate ?H for the reaction \(2 \mathrm{A}+\mathrm{B}_{2} \mathrm{C}_{3} \rightarrow 2 \mathrm{B}+\mathrm{A}_{2} \mathrm{C}_{3}\) \(2 \mathrm{A}+\frac{3}{2} \mathrm{C}_{2} \rightarrow \mathrm{A}_{2} \mathrm{C}_{3} \quad \Delta H=-1874 \mathrm{kJ}\) \(2 \mathrm{B}+\frac{3}{2} \mathrm{C}_{2} \rightarrow \mathrm{B}_{2} \mathrm{C}_{3} \quad \Delta H=-285 \mathrm{kJ}\)

Predict how the entropy of the system changes for the reaction \(\mathrm{CaCO}_{3}(\mathrm{s}) \rightarrow \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{g}) .\) Explain.

Which of these reactions would you expect to be spontaneous at relatively high temperatures? At relatively low temperatures? Explain a. \(C H_{3} O H(1) \rightarrow C H_{3} O H(g)\) b. \(C H_{3} O H(g) \rightarrow C H_{3} O H(1)\) c. \(C H_{3} O H(s) \rightarrow C H_{3} O H(1)\)

Explain how an exothermic reaction changes the entropy of the surroundings. Does the enthalpy change for such a reaction increase or decrease \(\Delta G_{\text { system }} ?\) Explain.

Calculate \(\Delta G_{\text { system for each process, and state whether }}\) the process is spontaneous or nonspontaneous. a) \(\Delta H_{\text { system }}=145 \mathrm{kJ}, T=293 \mathrm{K}, \Delta S_{\mathrm{system}}=195 \mathrm{JK}\) b) \(\Delta H_{\text { system }}=-232 \mathrm{kJ}, T=273 \mathrm{K}, \Delta S_{\text { system }}=138 \mathrm{J} / \mathrm{K}\) c) \(\Delta H_{\text { system }}=-15.9 \mathrm{kJ}, T=373 \mathrm{K}, \Delta S_{\text { syyttem }}=-268 \mathrm{J} / \mathrm{K}\)

Calculate the temperature at which \(\Delta G_{\text { system }}=0\) if \(\Delta H_{\text { system }}=4.88 \mathrm{kJ}\) and \(\Delta S_{\text { system }}=55.2 \mathrm{JK}\) .

For the change \(\mathrm{H}_{2} \mathrm{O}(1) \rightarrow \mathrm{H}_{2} \mathrm{O}(\mathrm{g}), \Delta G_{\mathrm{system}}^{\circ}\) is 8.557 \(\mathrm{kJ}\) and \(\Delta H_{\mathrm{system}}^{\circ}\) is 44.01 \(\mathrm{kJ.}\) What is \(\Delta S_{\mathrm{system}}^{\circ}\) for the change?

Is the following reaction to convert copper(II) sulfide to copper(II) sulfate spontaneous under standard conditions? \(\mathrm{CuS}(\mathrm{s})+2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CuSO}_{4}(\mathrm{s}) . \Delta H_{\mathrm{rxn}}^{\circ}=-718.3\) \(\mathrm{k} \mathrm{J},\) and \(\Delta S_{\mathrm{rxn}}^{\circ}=-368 \mathrm{J} / \mathrm{K} .\) Explain.

Bicycling Describe the energy conversions that occur when a bicyclist coasts down a long grade, then struggles to ascend a steep grade.

Hiking Imagine that on a cold day you are planning to take a thermos of hot soup with you on a hike. Explain why you might fill the thermos with hot water first before filling it with the hot soup.

Differentiate between the enthalpy of formation of \(\mathrm{H}_{2} \mathrm{O}(1)\) and \(\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) .\) Why is it necessary to specify the physical state of water in the following thermochemical equation \(\mathrm{CH}_{4}(\mathrm{g})+2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}_{2}(\mathrm{g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l} \text { or g })\) \(\Delta H=?\)

Apply Phosphorus trichloride is a starting material for the preparation of organic phosphorous compounds. Demonstrate how thermochemical equations a and b can be used to determine the enthalpy change for the reaction \(\mathrm{PCl}_{3}(1)+\mathrm{Cl}_{2}(\mathrm{g}) \rightarrow \mathrm{PCl}_{5}(\mathrm{s})\) a. \(P_{4}(s)+6 C l_{2}(g) \rightarrow 4 P C l_{3}(1) \quad \Delta H=-1280 \mathrm{kJ}\) b. \(P_{4}(s)+10 C l_{2}(g) \rightarrow 4 P C l_{5}(s) \qquad \Delta H=-1774 \mathrm{kJ}\)

Predict which of the two compounds, methane gas \(({CH}_{4})\) or methanal vapor \(({CH}_{2} {O})\) , has the greater molar enthalpy of combustion. Explain your answer. (Hint: Write and compare the balanced chemical equations for the two combustion reactions.)

Why is it necessary to perform repeated experiments in order to support a hypothesis? (Chapter 1)

Phosphorus has the atomic number 15 and an atomic mass of 31 amu. How many protons, neutrons, and electrons are in a neutral phosphorus atom? (Chapter 4)

What element has the electron configuration \([\mathrm{Ar}] 4 \mathrm{s}^{1} 3 \mathrm{d}^{5} ?(\text {Chapter } 5)\)

Name the following molecular compounds. (Chapter 8) a. \(S_{2} C I_{2}\) c. \(\mathrm{SO}_{3}\) b. \(\mathrm{CS}_{2}\) {d} . \(\mathrm{P}_{4} \mathrm{O}_{10}\)

Determine the molar mass for the following compounds. (Chapter 10) a. \(\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) b. \(\mathrm{Fe}(\mathrm{OH})_{3}\) d. the name of the compound is tetraphosphorus decoxide.

A sample of oxygen gas has a volume of 20.0 \(\mathrm{cm}^{3}\) at \(-10.0^{\circ} \mathrm{C}\) . What volume will this sample occupy if the temperature rises to \(110^{\circ} \mathrm{C} ?(\text {Chapter } 13)\)

What is the molarity of a solution made by dissolving 25.0 g of sodium thiocyanate (NaSCN) in enough water to make 500 mL of solution? (Chapter 14)

List three colligative properties of solutions. (Chapter 14)

Alternate Fuels Use library and Internet sources to explain how hydrogen might be produced, transported, and used as a fuel for automobiles. Summarize the benefits and drawbacks of using hydrogen as an alternative fuel for internal combustion engines

Wind Power Research the use of wind as a source of electrical power. Explain the possible benefits, disadvantages, and limitations of its use.