Calculate the temperature at which G system = 0 if H

A fruit-and-oatmeal bar contains 142 nutritional Calories. Convert this energy to calories.

An exothermic reaction releases 86.5 kJ. How many kilocalories of energy are released?

Challenge Define a new energy unit, named after yourself, with a magnitude of onetenth of a calorie. What conversion factors relate this new unit to joules? To Calories?

If the temperature of 34.4 g of ethanol increases from 25.0C to 78.8C, how much heat has been absorbed by the ethanol? Refer to Table 15.2.

A 155-g sample of an unknown substance was heated from 25.0C to 40.0C. In the process, the substance absorbed 5696 J of energy. What is the specific heat of the substance? Identify the substance among those listed in Table 15.2.

Challenge A 4.50-g nugget of pure gold absorbed 276 J of heat. The initial temperature was 25.0C. What was the final temperature?

Explain how energy changes from one form to another in an exothermic reaction. In an endothermic reaction.

Distinguish between kinetic and potential energy in the following examples: two separated magnets; an avalanche of snow; books on library shelves; a mountain stream; a stock-car race; separation of charge in a battery.

Explain how the light and heat of a burning candle are related to chemical potential energy

Calculate the amount of heat absorbed when 5.50 g of aluminum is heated from 25.0C to 95.0C. The specific heat of aluminum is 0.897 J/(gC).

Interpret Data Equal masses of aluminum, gold, iron, and silver were left to sit in the Sun at the same time and for the same length of time. Use Table 15.2 to arrange the four metals according to the increase in their temperatures from largest increase to smallest.

A 90.0-g sample of an unknown metal absorbed 25.6 J of heat as its temperature increased 1.18C. What is the specific heat of the metal?

The temperature of a sample of water increases from 20.0C to 46.6C as it absorbs 5650 J of heat. What is the mass of the sample?

How much heat is absorbed by a 2.00 10 3-g granite boulder ( c granite = 0.803 J/(gC)) as its temperature changes from 10.0C to 29.0C?

Challenge If 335 g of water at 65.5C loses 9750 J of heat, what is the final temperature of the water?

Describe how you would calculate the amount of heat absorbed or released by a substance when its temperature changes.

Explain why H for an exothermic reaction always has a negative value.

Explain why a measured volume of water is an essential part of a calorimeter

Explain why you need to know the specific heat of a substance in order to calculate how much heat is gained or lost by the substance as a result of a temperature change

Describe what the system means in thermodynamics, and explain how the system is related to the surroundings and the universe.

Calculate the specific heat in J/(gC) of an unknown substance if a 2.50-g sample releases 12.0 cal as its temperature changes from 25.0C to 20.0C.

Design an Experiment Describe a procedure you could follow to determine the specific heat of a 45-g piece of metal

Calculate the heat required to melt 25.7 g of solid methanol at its melting point. Refer to Table 15.4.

How much heat evolves when 275 g of ammonia gas condenses to a liquid at its boiling point? Use Table 15.4 to determine H cond.

Challenge What mass of methane (C H 4) must be burned in order to liberate 12,880 kJ of heat? Refer to Table 15.3 on page 529.

Write a complete thermochemical equation for the combustion of ethanol ( C 2 H 5 OH). H comb = -1367 kJ/mol

Determine Which of the following processes are exothermic? Endothermic? a. C 2 H 5 OH(l) C 2 H 5 OH(g) d. N H 3 (g) N H 3 (l) b. B r 2 (l) B r 2 (s) e. NaCl(s) NaCl(l) c. C 5 H 12 (g) + 8 O 2 (g) 5C O 2 (g) + 6 H 2 O(l)

Explain how you could calculate the heat released in freezing 0.250 mol water.

Calculate How much heat is released by the combustion of 206 g of hydrogen gas? H comb = -286 kJ/mol

Apply The molar heat of vaporization of ammonia is 23.3 kJ/mol. What is the molar heat of condensation of ammonia?

Interpret Scientific Illustrations The reaction A C is shown in the enthalpy diagram at right. Is the reaction exothermic or endothermic? Explain your answer. A C H Enthalpy

Use Equations a and b to determine H for the following reaction. 2CO(g) + 2NO(g) 2C O 2(g) + N 2(g) H = ? a. 2CO(g) + O 2(g) 2C O 2(g) H = -566.0 kJ b. N 2(g) + O 2(g) 2NO(g) H = -180.6 kJ

Challenge H for the following reaction is -1789 kJ. Use this and Equation a to determine H for Equation b. 4Al(s) + 3Mn O 2(s) 2A l 2O 3(s) + 3Mn(s) H = -1789 kJ a. 4Al(s) + 3 O 2(g) 2A l 2O 3(s) H = -3352 kJ b. Mn(s) + O 2(g) Mn O 2(s) H = ?

Show how the sum of enthalpy of formation equations produces each of the following reactions. You do not need to look up and include H values. a. 2NO(g) + O 2(g) 2N O 2(g) b. S O 3(g) + H 2O(l) H 2S O 4(aq)

Use standard enthalpies of formation from Table R-11 on page 975 to calculate H rxn for the following reaction. 4N H 3(g) + 7 O 2(g) 4N O 2(g) + 6 H 2O(l)

Determine H comb for butanoic acid, C 3H 7COOH(l) + 5 O 2(g) 4C O 2(g) + 4 H 2O(l). Use data in Table R-11 on page 975 and the following equation. 4C(s) + 4 H 2(g) + O 2(g) C 3H 7COOH(l) H = -534 kJ

Challenge Two enthalpy of formation equations, a and b, combine to form the equation for the reaction of nitrogen oxide and oxygen. The product of the reaction is nitrogen dioxide: NO(g) + _1 2O 2(g) N O 2(g) H rxn = -58.1 kJ a. _1 2N 2(g) + _1 2O 2(g) NO(g) H f = 91.3 kJ b. _1 2N 2(g) + O 2(g) N O 2(g) H f = ? What is H f for Equation b?

Explain what is meant by Hesss law and how it is used to determine H rxn .

Explain in words the formula that can be used to determine H rxn when using Hesss law.

Describe how the elements in their standard states are defined on the scale of standard enthalpies of formations.

Examine the data in Table 15.5 on page 538. What conclusion can you draw about the stabilities of the compounds listed relative to the elements in their standard states? Recall that low energy is associated with stability

Calculate Use Hesss law to determine H for the reaction NO(g) + O(g) N O 2 (g) H = ? given the following reactions. Show your work. O 2 (g) 2O(g) H = +495 kJ 2 O 3 (g) 3 O 2 (g) H = -427 kJ NO(g) + O 3 (g) N O 2 (g) + O 2 (g) H = -199 kJ

Interpret Scientific Illustrations Use the data below to draw a diagram of standard heats of formation similar to Figure 15.15 on page 538 and use your diagram to determine the heat of vaporization of water at 298 K. Liquid water: H f = -285.8 kJ/mol Gaseous water: H f = -241.8 kJ/mol

Predict the sign of S system for each of the following changes. a. ClF(g) + F 2(g) Cl F 3(g) c. C H 3OH(l) C H 3OH(aq) b. N H 3(g) N H 3(aq) d. C 10H 8(l) C 10H 8(s)

Challenge Comment on the sign of S system for the following reaction. Fe(s) + Z n 2+(aq) F e 2+(aq) + Zn(s)

Determine whether each of the following reactions is spontaneous. a. H system = -75.9 kJ, T = 273 K, S system = 138 J/K c. H system = 365 kJ, T = 388 K, S system = -55.2 J/K b. H system = -27.6 kJ, T = 535 K, S system = -55.2 J/K d. H system = 452 kJ, T = 165 K, S system = 55.7 J/K

Challenge Given H system = -144 kJ and S system = -36.8 J/K for a reaction, determine the lowest temperature in kelvins at which the reaction would be spontaneous.

Compare and contrast spontaneous and nonspontaneous reactions.

Describe how a systems entropy changes if the system becomes more disordered during a process.

Decide Does the entropy of a system increase or decrease when you dissolve a cube of sugar in a cup of tea? Define the system, and explain your answer.

Determine whether the system H system = -20.5 kJ, T = 298 K, and S system = -35.0 J/K is spontaneous or nonspontaneous.

Outline Use the blue and red headings to outline the section. Under each heading, summarize the important ideas discussed.

Compare and contrast temperature and heat

How does the chemical potential energy of a system change during an endothermic reaction?

Describe a situation that illustrates potential energy changing to kinetic energy.

Cars How is the energy in gasoline converted and released when it burns in an automobile engine?

Nutrition How does the nutritional Calorie compare with the calorie? What is the relationship between the Calorie and a kilocalorie?

What quantity has the units J/(gC)?

Describe what might happen in Figure 15.22 when the air above the surface of the lake is colder than the water

Ethanol has a specific heat of 2.44 J/(gC). What does this mean?

Explain how the amount of energy required to raise the temperature of an object is determined.

Nutrition A food item contains 124 nutritional Calories. How many calories does the food item contain?

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 25.0C to 78.0C. What is the specific heat of the alloy?

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

Is the reaction shown in Figure 15.23 endothermic or exothermic? How do you know?

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 41.2C to -12.9C? The specific heat of granite is 0.803 J/(gC).

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 18.4C, how much heat must be added to the water to raise its temperature to 29.0C? Assume that the density of water is 1.000 g/mL

How much heat is absorbed by a 44.7-g piece of lead when its temperature increases by 65.4C?

Food Preparation When 10.2 g of canola oil at 25.0C is placed in a wok, 3.34 kJ of heat is required to heat it to a temperature of 196.4C. 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 106.1C, while the temperature of the water increases by 10.5C. What is the specific heat of the alloy?

Write the sign of H system for each of the following changes in physical state. a. C 2 H 5 OH(s) C 2 H 5 OH(l) b. H 2 O(g) H 2 O(l) c. C H 3 OH(l) C H 3 OH(g) d. N H 3 (l) N H 3 (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.

Write the thermochemical equation for the combustion of methane. Refer to Table 15.3.

Use information from Figure 15.24 to calculate how much heat is required to vaporize 4.33 mol of water at 100C.

Agriculture Water is sprayed on oranges during a frosty night. If an average of 11.8 g of water freezes on each orange, how much heat is released?

Grilling What mass of propane ( C 3 H 8 ) must be burned in a barbecue grill to release 4560 kJ of heat? The H comb of propane is -2219 kJ/mol.

Heating with Coal How much heat is liberated when 5.00 kg of coal is burned if the coal is 96.2% carbon by mass and the other materials in the coal do not react? H comb of carbon is -394 kJ/mol.

How much heat is evolved when 1255 g of water condenses to a liquid at 100C?

A sample of ammonia ( H solid = -5.66 kJ/mol) liberates 5.66 kJ of heat as it solidifies at its melting point. What is the mass of the sample?

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 Figure 15.25 to write the thermochemical equation for the formation of 1 mol of aluminum chloride (a solid in its standard state) from its constituent elements in their standard states.

Use standard enthalpies of formation from Table R-11 on page 975 to calculate H rxn for the following reaction. P 4 O 6 (s) + 2 O 2 (g) P 4 O 10 (s)

Use Hesss law and the following thermochemical equations to produce the thermochemical equation for the reaction C(s, diamond) C(s, graphite). What is H for the reaction? a. C(s, graphite) + O 2 (g) C O 2 (g) H = -394 kJ b. C(s, diamond) + O 2 (g) C O 2 (g) H = -396 kJ

Use Hesss law and the changes in enthalpy for the following two generic reactions to calculate H for the reaction 2A + B 2 C 3 2B + A 2 C 3 . 2A + _3 2 C 2 A 2 C 3 H = -1874 kJ 2B + _3 2 C 2 B 2 C 3 H = -285 kJ

Under what conditions is an endothermic chemical reaction in which the entropy of the system increases likely to be spontaneous?

Predict how the entropy of the system changes for the reaction CaC O 3 (s) CaO(s) + C O 2 (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 OH(l) C H 3 OH(g) b. C H 3 OH(g) C H 3 OH(l) c. C H 3 OH(s) C H 3 OH(l)

Explain how an exothermic reaction changes the entropy of the surroundings. Does the enthalpy change for such a reaction increase or decrease G system ? Explain.

Calculate G system for each process, and state whether the process is spontaneous or nonspontaneous. a. H system = 145 kJ, T = 293 K, S system = 195 J/K b. H system = -232 kJ, T = 273 K, S system = 138 J/K c. H system = -15.9 kJ, T = 373 K, S system = -268 J/K

Calculate the temperature at which G system = 0 if H system = 4.88 kJ and S system = 55.2 J/K.

For the change H 2 O(l) H 2 O(g), G system is 8.557 kJ and H system is 44.01 kJ. What is S system for the change?

Is the following reaction to convert copper(II) sulfide to copper(II) sulfate spontaneous under standard conditions? CuS(s) + 2 O 2 (g) CuS O 4 (s). H rxn = -718.3 kJ, and S rxn = -368 J/K. Explain.

Calculate the temperature at which G system = -34.7 kJ if H system = -28.8 kJ and S system = 22.2 J/K.

Heat was added consistently to a sample of water to produce the heating curve in Figure 15.26. Identify what is happening in Sections 1, 2, 3, and 4 on the curve.

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 H 2 O(l) and H 2 O(g). Why is it necessary to specify the physical state of water in the following thermochemical equation C H 4 (g) + 2 O 2 (g) C O 2 (g) + 2 H 2 O(l or g) H = ?

Analyze both of the images in Figure 15.27 in terms of potential energy of position, chemical potential energy, kinetic energy, and heat.

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 PC l 3 (l) + C l 2 (g) PC l 5 (s). a. P 4 (s) + 6C l 2 (g) 4PC l 3 (l) H = -1280 kJ b. P 4 (s) + 10C l 2 (g) 4PC l 5 (s) H = -1774 kJ

Calculate Suppose that two pieces of iron, one with a mass exactly twice the mass of the other, are placed in an insulated calorimeter. If the original temperatures of the larger piece and the smaller piece are 90.0C and 50.0C, respectively, what is the temperature of the two pieces when thermal equilibrium has been established? Refer to Table R-9 on page 975 for the specific heat of iron.

Predict which of the two compounds, methane gas (C H 4 ) or methanal vapor (C H 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.)

A sample of natural gas is analyzed and found to be 88.4% methane (C H 4 ) and 11.6% ethane ( C 2 H 6 ) by mass. The standard enthalpy of combustion of methane to gaseous carbon dioxide (C O 2 ) and liquid water ( H 2 O) is -891 kJ/mol. Write the equation for the combustion of gaseous ethane to carbon dioxide and water. Calculate the standard enthalpy of combustion of ethane using standard enthalpies of formation from Table R-11 on page 975. Using that result and the standard enthalpy of combustion of methane in Table 15.3, calculate the energy released by the combustion of 1 kg of natural gas

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 [Ar]4 s 1 3 d 5 ? (Chapter 5)

Name the following molecular compounds. (Chapter 8) a. S 2 C l 2 c. S O 3 b. C S 2 d. P 4 O 10

Determine the molar mass for the foloowing compounds. (Chapter 10) a. Co(N O 3 ) 2 6 H 2 O b. Fe(OH ) 3

What kind of chemical bond is represented by the dotted lines in Figure 15.28? (Chapter 12)

A sample of oxygen gas has a volume of 20.0 c m 3 at -10.0C. What volume will this sample occupy if the temperature rises to 110 C? (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.

Which of the oils tested provided the greatest amount of energy per unit mass when burned?

According to the data, how much energy would be liberated by burning 0.554 kg of olive oil?

Assume that 12.2 g of soy oil is burned and that all the energy released is used to heat 1.600 kg of water, initially at 20.0C. What is the final temperature of the water?

Oils can be used as fuels. How many grams of canola oil would have to be burned to provide the energy to vaporize 25.0 g of water. ( Hvap = 40.7 kJ/mol).