When 1 mol of CS2(l) forms from its elements at 1 atm and

Why do heat (q) and work (w) have positive values when entering a system and negative values when leaving?

If you feel warm after exercising, have you increased the internal energy of your body? Explain

An adiabatic process is one that involves no heat transfer. What is the relationship between work and the change in internal energy in an adiabatic process?

State two ways that you increase the internal energy of your body and two ways that you decrease it.

Name a common device that is used to accomplish each energy change: (a) Electrical energy to thermal energy (b) Electrical energy to sound energy (c) Electrical energy to light energy (d) Mechanical energy to electrical energy (e) Chemical energy to electrical energy

In winter, an electric heater uses a certain amount of electrical energy to heat a room to 20 C. In summer, an air conditioner uses the same amount of electrical energy to cool the room to 20 C. Is the change in internal energy of the heater larger, smaller, or the same as that of the air conditioner? Explain.

Imagine lifting your textbook into the air and dropping it onto a desktop. Describe all the energy transformations (from one form to another) that occur, moving backward in time from a moment after impact.

A system receives 425 J of heat and delivers 425 J of work to its surroundings. What is the change in internal energy of the system (in J)?

A system conducts 255 cal of heat to the surroundings while delivering 428 cal of work. What is the change in internal energy of the system (in cal)?

What is the change in internal energy (in J) of a system that releases 675 J of thermal energy to its surroundings and has 530 cal of work done on it?

What is the change in internal energy (in J) of a system that absorbs 0.615 kJ of heat from its surroundings and has 0.247 kcal of work done on it?

Complete combustion of 2.0 metric tons of coal (assuming pure carbon) to gaseous carbon dioxide releases 6.6 10 10 J of heat. Convert this energy to (a) kilojoules; (b) kilocalories; (c) British thermal units

Thermal decomposition of 5.0 metric tons of limestone to lime and carbon dioxide requires 9.0 10 6 kJ of heat. Convert this energy to (a) joules; (b) calories; (c) British thermal units

The nutritional calorie (Calorie) is equivalent to 1 kcal. One pound of body fat is equivalent to about 4.1 10 Calories. Express this quantity of energy in joules and kilojoules

If an athlete expends 1950 kJ/h, how long does she have to play to work off 1.0 lb of body fat? (See Problem 6.14.)

Why is the work done when a system expands against a constant external pressure assigned a negative sign?

Why is it usually more convenient to measure H than E?

Hot packs used by skiers, climbers, and others for warmth are based on the crystallization of sodium acetate from a highly concentrated solution. What is the sign of H for this crystallization? Is the reaction exothermic or endothermic?

Classify the following processes as exothermic or endothermic: (a) freezing of water; (b) boiling of water; (c) digestion of food; (d) a person running; (e) a person growing; (f) wood being chopped; (g) heating with a furnace.

What are the two main components of the internal energy of a substance? On what are they based?

For each process, state whether H is less than (more negative), equal to, or greater than E of the system. Explain. (a) An ideal gas is cooled at constant pressure. (b) A mixture of gases undergoes an exothermic reaction in a container of fixed volume.(c) A solid yields a mixture of gases in an exothermic reaction that takes place in a container of variable volume.

Draw an enthalpy diagram for a general exothermic reaction; label the axis, reactants, products, and H with its sign

Draw an enthalpy diagram for a general endothermic reaction; label the axis, reactants, products, and H with its sign.

Write a balanced equation and draw an approximate enthalpy diagram for each of the following: (a) the combustion of 1 mol of ethane in oxygen; (b) the freezing of liquid water.

Write a balanced equation and draw an approximate enthalpy diagram for each of the following: (a) the formation of 1 mol of sodium chloride from its elements (heat is released); (b) the vaporization of liquid benzene.

Write a balanced equation and draw an approximate enthalpy diagram for each of the following changes: (a) the combustion of 1 mol of liquid methanol (CH3OH); (b) the formation of 1 mol of nitrogen dioxide from its elements (heat is absorbed).

Write a balanced equation and draw an approximate enthalpy diagram for each of the following changes: (a) the sublimation of dry ice [conversion of CO2(s) directly to CO2(g)]; (b) the reaction of 1 mol of sulfur dioxide with oxygen.

The circles below represent a phase change occurring at constant temperature: Is the value of each of the following positive ( ), negative ( ), or zero: (a) qsys; (b) E sys; (c) E univ?

The piston-cylinder assemblies below represent a physical change occurring at constant pressure: (a) Is wsys , , or 0? (b) Is H sys , , or 0? (c) Can you determine whether E surr is , , or 0? Explain.

Why can we measure only changes in enthalpy, not absolute enthalpy values?

What data do you need to determine the specific heat capacity of a substance?

Is the specific heat capacity of a substance an intensive or extensive property? Explain.

Distinguish between specific heat capacity and heat capacity. Which parameter would you more likely use if you 1.05 atm 1.05 atm 262 Chapter 6 Thermochemistry: Energy Flow and Chemical Change siL48593_ch06_235-267 9:2:07 20:06pm Page 262 nishant-13 ve403:MHQY042:siL5ch06: Apago PDF Enhancer were calculating heat changes in (a) a chrome-plated, brass bathroom fixture; (b) a sample of high-purity copper wire; (c) a sample of pure water? Explain

Both a coffee-cup calorimeter and a bomb calorimeter can be used to measure the heat involved in a reaction. Which measures E and which measures H? Explain.

Find q when 22.0 g of water is heated from 25. C to 100. C

Calculate q when 0.10 g of ice is cooled from 10. C to 75 C ( cice 2.087 J/g K).

A 295-g aluminum engine part at an initial temperature of 13.00 C absorbs 75.0 kJ of heat. What is the final temperature of the part (c of Al 0.900 J/g K)?

A 27.7-g sample of ethylene glycol, a car radiator coolant, loses 688 J of heat. What was the initial temperature of the ethylene glycol if the final temperature is 32.5 C (c of ethylene glycol 2.42 J/g K)?

Two iron bolts of equal massone at 100. C, the other at 55 Care placed in an insulated container. Assuming the heat capacity of the container is negligible, what is the final temperature inside the container (c of iron 0.450 J/g K)?

One piece of copper jewelry at 105 C has exactly twice the mass of another piece, which is at 45 C. Both pieces are placed inside a calorimeter whose heat capacity is negligible. What is the final temperature inside the calorimeter (c of copper 0.387 J/g K)?

When 155 mL of water at 26 C is mixed with 75 mL of water at 85 C, what is the final temperature? (Assume that no heat is lost to the surroundings; d of water is 1.00 g/mL.)

An unknown volume of water at 18.2 C is added to 24.4 mL of water at 35.0 C. If the final temperature is 23.5 C, what was the unknown volume? (Assume that no heat is lost to the surroundings; d of water is 1.00 g/mL.)

A 455-g piece of copper tubing is heated to 89.5 C and placed in an insulated vessel containing 159 g of water at 22.8 C. Assuming no loss of water and a heat capacity for the vessel of 10.0 J/K, what is the final temperature of the system (c of copper 0.387 J/g K)?

A 30.5-g sample of an alloy at 93.0 C is placed into 50.0 g of water at 22.0 C in an insulated coffee cup with a heat capacity of 9.2 J/K. If the final temperature of the system is 31.1 C, what is the specific heat capacity of the alloy?

High-purity benzoic acid (C6H5COOH; H rxn for combustion ? ? 3227 kJ/mol) is used as a standard for calibrating bomb calorimeters. A 1.221-g sample burns in a calorimeter (heat capacity 1365 J/ C) that contains exactly 1.200 kg of water. What temperature change is observed?

Two aircraft rivets, one of iron and the other of copper, are placed in a calorimeter that has an initial temperature of 20. C. The data for the metals are as follows: (a) Will heat flow from Fe to Cu or from Cu to Fe? (b) What other information is needed to correct any measurements that would be made in an actual experiment? (c) What is the maximum final temperature of the system (assuming the heat capacity of the calorimeter is negligible)?

A chemical engineer studying the properties of fuels placed 1.520 g of a hydrocarbon in the bomb of a calorimeter and filled it with O2 gas (see Figure 6.10, p. 248). The bomb was immersed in 2.550 L of water and the reaction initiated. The water temperature rose from 20.00 C to 23.55 C. If the calorimeter (excluding the water) had a heat capacity of 403 J/K, what was the heat of reaction for combustion (qV) per gram of the fuel?

When 25.0 mL of 0.500 M H2SO4 is added to 25.0 mL of 1.00 M KOH in a coffee-cup calorimeter at 23.50 C, the temperature rises to 30.17 C. Calculate H of this reaction. (Assume that the total volume is the sum of the individual volumes and that the density and specific heat capacity of the solution are the same as for pure water.)

Does a negative H rxn mean that the heat of reaction can be thought of as a reactant or as a product?

ght of as a reactant or as a product? 6.50 Would you expect to have a positive or a negative H rxn? Explain.

Is H positive or negative when 1 mol of water vapor condenses to liquid water? Why? How does this value compare with that for the vaporization of 2 mol of liquid water to water vapor?

Consider the following balanced thermochemical equation for a reaction sometimes used for H2S production: (a) Is this an exothermic or endothermic reaction? (b) What is H rxn for the reverse reaction? (c) What is H when 2.6 mol of S8 reacts? (d) What is H when 25.0 g of S8 reacts?

Consider the following balanced thermochemical equation for the decomposition of the mineral magnesite: (a) Is heat absorbed or released in the reaction? (b) What is H rxn for the reverse reaction? (c) What is H when 5.35 mol of CO2 reacts with excess MgO? (d) What is H when 35.5 g of CO2 reacts with excess MgO?

When 1 mol of NO(g) forms from its elements, 90.29 kJ of heat is absorbed. (a) Write a balanced thermochemical equation for this reaction. (b) How much heat is involved when 3.50 g of NO decomposes to its elements?

When 1 mol of KBr(s) decomposes to its elements, 394 kJ of heat is absorbed. (a) Write a balanced thermochemical equation for this reaction. (b) How much heat is released when 10.0 kg of KBr forms from its elements?

Liquid hydrogen peroxide, an oxidizing agent in many rocket fuel mixtures, releases oxygen gas on decomposition: How much heat is released when 652 kg of H2O2 decomposes?

Compounds of boron and hydrogen are remarkable for their unusual bonding (described in Section 14.5) and also for their 2H2O2(l) 2H2O(l) O2(g) Hrxn ? ? 196.1 kJ MgCO3(s) MgO(s) CO2(g) Hrxn 117.3 kJ 1 8S8(s) H2(g) H2S(g) Hrxn ? ? 20.2 kJ O2(g) 2O(g) Problems 263 siL48593_ch06_235-267 9:2:07 20:06pm Page 263 nishant-13 ve403:MHQY042:siL5ch06: Apago PDF Enhancer reactivity. With the more reactive halogens, for example, diborane (B2H6) forms trihalides even at low temperatures: How much heat is released per kilogram of diborane that reacts?

Deterioration of buildings, bridges, and other structures through the rusting of iron costs millions of dollars every day. Although the actual process also requires water, a simplified equation (with rust shown as Fe2O3) is (a) How much heat is evolved when 0.250 kg of iron rusts? (b) How much rust forms when 4.85 10 3 kJ of heat is released?

A mercury mirror forms inside a test tube as a result of the thermal decomposition of mercury(II) oxide: (a) How much heat is needed to decompose 555 g of the oxide? (b) If 275 kJ of heat is absorbed, how many grams of Hg form?

Ethylene (C2H4) is the starting material for the preparation of polyethylene. Although typically made during the processing of petroleum, ethylene occurs naturally as a fruit-ripening hormone and as a component of natural gas. (a) The heat of reaction for the combustion of C2H4 is 1411 kJ/mol. Write a balanced thermochemical equation for the combustion of C2H4. (b) How many grams of C2H4 must burn to give 70.0 kJ of heat?

Sucrose (C12H22O11, table sugar) is oxidized in the body by O2 via a complex set of reactions that ultimately produces CO2(g) and H2O(g) and releases 5.64 10 3 kJ/mol sucrose. (a) Write a balanced thermochemical equation for this reaction. (b) How much heat is released per gram of Apago

Express Hesss law in your own words

What is the main use of Hesss law?

It is very difficult to burn carbon in a deficiency of O2 and produce only CO; some CO2 forms as well. However, carbon burns in excess O2 to form only CO2, and CO burns in excess O2 to form only CO2. Use the heats of the latter two reactions (from Appendix B) to calculate H rxn for the following reaction: Skill-Building Exercises (grouped in similar pairs)

Calculate H rxn for given the following set of reactions:

Calculate H rxn for given the following set of reactions:

Write the balanced overall equation (equation 3) for the following process, calculate Hoverall, and match the number of each equation with the letter of the appropriate arrow in Figure P6.67:

Write the balanced overall equation (equation 3) for the following process, calculate Hoverall, and match the number of each equation with the letter of the appropriate arrow in Figure P6.68:

At a given set of conditions, 241.8 kJ is given off when 1 mol of H2O(g) forms from its elements. Under the same conditions, 285.8 kJ is given off when 1 mol of H2O(l) forms from its elements. Find the heat of vaporization of water at these conditions

When 1 mol of CS2(l) forms from its elements at 1 atm and 25 C, 89.7 kJ is absorbed, and it takes 27.7 kJ to vaporize 1 mol of the liquid. How much heat is absorbed when 1 mol of CS2(g) forms from its elements at these conditions?

Diamond and graphite are two crystalline forms of carbon. At 1 atm and 25 C, diamond changes to graphite so slowly that the enthalpy change of the process must be obtained indirectly. Determine H rxn for with equations from the following list:

What is the difference between the standard heat of formation and the standard heat of reaction?

How are H f values used to calculate H rxn?

Make any changes needed in each of the following equations to make H rxn equal to H f for the compound present:

Use Table 6.3 or Appendix B to write a balanced formation equation at standard conditions for each of the following compounds: (a) CaCl2; (b) NaHCO3; (c) CCl4; (d) HNO3

Use Table 6.3 or Appendix B to write a balanced formation equation at standard conditions for each of the following compounds: (a) HI; (b) SiF4; (c) O3; (d) Ca3(PO4)2.

Calculate H rxn for each of the following:

8 Calculate H rxn for each of the following:

Copper(I) oxide can be oxidized to copper(II) oxide:

Acetylene burns in air according to the following equation:

The common lead-acid car battery produces a large burst of current, even at low temperatures, and is rechargeable. The reaction that occurs while recharging a dead battery is

Stearic acid (C18H36O2) is a typical fatty acid, a molecule with a long hydrocarbon chain and an organic acid group (COOH) at the end. It is used to make cosmetics, ointments, soaps, and candles and is found in animal tissue as part of many saturated fats. In fact, when you eat meat, chances are that you are ingesting some fats that contain stearic acid. (a) Write a balanced equation for the complete combustion of stearic acid to gaseous products. (b) Calculate H rxn for this combustion ( H f of C18H36O2 948 kJ/mol). (c) Calculate the heat (q) in kJ and kcal when 1.00 g of stearic acid is burned completely. (d) Nutritional information for a candy bar states that one serving contains 11.0 g of fat and 100. Cal from fat (1 Cal 1 kcal). Is this information consistent with your answer for (c)?

Care must be taken when diluting sulfuric acid with water, because the dilution process is highly exothermic: (a) Use Appendix B to find H for diluting 1.00 mol of H2SO4(l) (d 1.83 g/mL) to 1 L of 1.00 M H2SO4(aq) (d 1.060 g/mL). (b) Suppose you carry out the dilution in a calorimeter. The initial T is 25.0 C, and the specific heat capacity of the final solution is 3.50 J/g K. What is the final T? (c) Use the ideas of density and heat capacity to explain why you should add acid to water rather than water to acid.

A balloonist is preparing to make a trip in a helium-filled balloon. The trip begins in early morning when the temperature is 15 C. By midafternoon, the temperature has increased to 30. C.Assuming the pressure remains constant at 1.00 atm, for each mole of helium, calculate: (a) The initial and final volumes. (b) The change in internal energy, E [Hint: Helium behaves like an ideal gas, so . Be sure the units of R are consistent with those of E]. (c) The work (w) done by the helium (in J). (d) The heat (q) transferred (in J). (e) H for the process (in J). (f) Explain the relationship between the answers to (d) and (e).

In winemaking, the sugars in grapes undergo fermentation by yeast to yield CH3CH2OH and CO2. During cellular respiration, sugar and ethanol are burned to water vapor and CO2. (a) Using C6H12O6 for sugar, calculate H rxn of fermentation and of respiration (combustion). (b) Write a combustion reaction for ethanol. Which has a higher H rxn for combustion per mole of C, sugar or ethanol?

Three of the reactions that occur when the paraffin of a candle (typical formula C21H44) burns are as follows: (1) Complete combustion forms CO2 and water vapor. (2) Incomplete combustion forms CO and water vapor. (3) Some wax is oxidized to elemental C (soot) and water vapor. (a) Find H rxn of each reaction ( H f of C21H44 ? ? 476 kJ/mol; use graphite for elemental carbon). (b) Find q (in kJ) when a 254-g candle burns completely. (c) Find q (in kJ) when 8.00% by mass of the candle burns incompletely and another 5.00% undergoes soot formation.

Ethylene oxide (EO) is prepared by the vapor-phase oxidation of ethylene. Its main uses are in the preparation of the antifreeze ethylene glycol and in the production of poly(ethylene terephthalate), which is used to make beverage bottles and fibers. Pure EO vapor can decompose explosively: Liquid EO has H f ? ? 77.4 kJ/mol and H vap 569.4 J/g. (a) Calculate Hrxn for the gas-phase reaction. (b) Due to external heating, the vapor decomposes at 10 bar and 93 C in a distillation column. What is the final temperature if the average specific heat capacity of the products is 2.5 J/g C?

The following scenes represent a gaseous reaction between compounds of nitrogen (blue) and oxygen (red) at 298 K: (a) Write a balanced equation and use Appendix B to calculate Hrxn. (b) If each molecule of product represents 1.50 10 2 mol, what quantity of heat (in J) is released or absorbed?

Isooctane (C8H18; d 0.692 g/mL) is used as the fuel in a test of a new automobile drive train. (a) How much energy (in kJ) is released by complete combustion of the isooctane in a 20.4-gal fuel tank to gases ( H rxn 5.44 10 3 kJ/mol)? (b) The energy delivered to the wheels at 65 mph is 5.5 104 kJ/h. Assuming all the energy is transferred to the wheels, what is the cruising range (in km) of the car on a full tank? (c) If the actual range is 455 miles, explain your answer to (b)

Four 50.-g samples of different liquids are placed in beakers at Tinitial of 25.00 C. Each liquid is heated until 450. J is absorbed; Tfinal is shown on each beaker below. Rank the liquids in order of increasing specific heat capacity

Oxidation of gaseous ClF by F2 yields liquid ClF3, an important fluorinating agent. Use the following thermochemical equations to calculate H rxn for the production of ClF3:

Silver bromide is used to coat ordinary black-and-white photographic film, while high-speed film uses silver iodide. (a) When 50.0 mL of 5.0 g/L AgNO3 is added to a coffee-cup calorimeter containing 50.0 mL of 5.0 g/L NaI, with both solutions at 25 C, what mass of AgI forms? (b) Use Appendix B to find H rxn. (c) What is T soln (assume the volumes are additive and the solution has the density and specific heat capacity of water)?

The calorie (4.184 J) was originally defined as the quantity of energy required to raise the temperature of 1.00 g of liquid water 1.00 C. The British thermal unit (Btu) is defined as the quantity of energy required to raise the temperature of 1.00 lb of liquid water 1.00 F. (a) How many joules are in 1.00 Btu (1 lb 453.6 g; a change of 1.0 C 1.8 F)? (b) The therm is a unit of energy consumption and is defined as 100,000 Btu. How many joules are in 1.00 therm? (c) How many moles of methane must be burned to give 1.00 therm of energy? (Assume water forms as a gas.) (d) If natural gas costs $0.66 per therm, what is the cost per mole of methane? (Assume natural gas is pure methane.) (e) How much would it cost to warm 318 gal of water in a hot tub from 15.0 C to 42.0 C (1 gal 3.78 L)?

Whenever organic matter is decomposed under oxygen-free (anaerobic) conditions, methane is one of the products. Thus, enormous deposits of natural gas, which is almost entirely methane, serve as a major source of fuel for home and industry. (a) Known sources of natural gas can produce 5600 EJ of energy (1 EJ 1018 J). Current total global energy usage is 4.0 10 2 EJ per year. Find the mass (in kg) of known sources of natural gas ( H rxn for the combustion of CH4 ? ? 802 kJ/mol). (b) For how many years could these sources supply the worlds total energy needs? (c) What volume (in ft3 ) of natural gas, measured at STP, is required to heat 1.00 qt of water from 25.0 C to 100.0 C (d of H2O 1.00 g/mL; d of CH4 at STP 0.72 g/L)? (d) The fission of 1 mol of uranium (about 4 10 4 ft3 ) in a nuclear reactor produces 2 10 13 J. What volume (in ft3 ) of natural gas would produce the same amount of energy?

A reaction is carried out in a steel vessel within a chamber filled with argon gas. Shown below are molecular views of the argon adjacent to the surface of the reaction vessel before and after the rea

For each of the following events, the system is in italics. State whether heat, work, or both is (are) transferred, and specify the direction of each transfer. (a) You pump air into an automobile tire. (b) A tree rots in a forest. (c) You strike a match. (d) You cool juice in a refrigerator. (e) You cook food on a kitchen range

To make use of ionic hydrates for storing solar energy (see Chemical Connections, p. 259), you place 500.0 kg of sodium sulfate decahydrate on your house roof. Assuming complete reaction and 100% efficiency of heat transfer, how much heat (in kJ) is released to your house at night?

An aqueous waste stream that has a maximum concentration of 0.50 M H2SO4 (d 1.030 g/mL at 25 C) will be neutralized by controlled addition of 40% caustic soda (NaOH; d 1.430 g/L) before it goes to the process sewer and then to the chemical plant waste treatment facility. However, a safety review finds that the waste stream could meet a small stream of an immiscible organic compound, which could form a flammable vapor in air at 40. C. The maximum temperature of the caustic soda and the waste stream is 31 C. Could the temperature increase due to the heat of neutralization cause the vapor to explode? Assume the specific heat capacity of each solution is 4.184 J/g K

Kerosene, a common space-heater fuel, is a mixture of hydrocarbons whose average formula is C12H26. (a) Write a balanced equation, using the simplest whole-number coefficients, for the complete combustion of kerosene to gases. (b) If H rxn ? ? 1.50 10 4 kJ for the combustion equation as written in part (a), determine H f of kerosene. (c) Calculate the heat produced by combustion of 0.50 gal of kerosene (d of kerosene 0.749 g/mL). (d) How many gallons of kerosene must be burned for a kerosene furnace to produce 1250. Btu (1 Btu 1.055 kJ)?

Coal gasification is a multistep process to convert coal into cleaner-burning fuels (see Chemical Connections, p. 256). In one step, a coal sample reacts with superheated steam: (a) Combine this reaction with the following two to write an overall reaction for the production of methane: (b) Calculate H rxn for this overall change. CO(g) 3H2(g) CH4(g) H2O(g) Hrxn ? ? 206 kJ CO(g) H2O(g) CO2(g) H2(g) Hrxn ? ? 41 kJ C(coal) H2O(g) CO(g) H2(g) Hrxn 129.7 kJ Before reaction Container Wall Container Wall After reaction 266 Chapter 6 Thermochemistry: Energy Flow and Chemical Change siL48593_ch06_235-267 9:2:07 20:06pm Page 266 nishant-13 ve403:MHQY042:siL5ch06: Apago PDF Enhancer (c) Using the value in (b) and calculating H rxn for the combustion of methane, find the total heat for gasifying 1.00 kg of coal and burning the methane formed (assume water forms as a gas and of coal 12.00 g/mol)

Phosphorus pentachloride is used in the industrial preparation of organic phosphorus compounds. Equation 1 shows its preparation from PCl3 and Cl2: (1) Use equations 2 and 3 to calculate H rxn of equation 1:

Consider the following hydrocarbon fuels: (a) Rank them in terms of heat released (a) per mole and (b) per gram. [Assume H2O(g) forms and combustion is complete.]

A typical candy bar weighs about 2 oz (1.00 oz 28.4 g). (a) Assuming that a candy bar is 100% sugar and that 1.0 g of sugar is equivalent to about 4.0 Calories of energy, calculate the energy (in kJ) contained in a typical candy bar. (b) Assuming that your mass is 58 kg and you convert chemical potential energy to work with 100% efficiency, how high would you have to climb to work off the energy in a candy bar? (Potential energy mass g height, where g 9.8 m/s2 .) (c) Why is your actual conversion of potential energy to work less than 100% efficient?

Silicon tetrachloride is produced annually on the multikiloton scale for making transistor-grade silicon. It can be made directly from the elements (reaction 1) or, more cheaply, by heating sand and graphite with chlorine gas (reaction 2). If water is present in reaction 2, some tetrachloride may be lost in an unwanted side reaction (reaction 3): (1) (2) (3) (a) Use reaction 3 to calculate the heats of reaction of reactions 1 and 2. (b) What is the heat of reaction for the new reaction that is the sum of reactions 2 and 3?

Use the following information to find H f of gaseous HCl: N2(g) 3H2(g) 2NH3(g) H rxn ? ?91.8 kJ N2(g) 4H2(g) Cl2(g) 2NH4Cl(s) H rxn ? ?628.8 kJ NH3(g) HCl(g) NH4Cl(s) H rxn ? ?176.2 kJ

You want to determine H for the reaction (a) To do so, you first determine the heat capacity of a calorimeter using the following reaction, whose H is known: Calculate the heat capacity of the calorimeter from these data: Amounts used: 50.0 mL of 2.00 M HCl and 50.0 mL of 2.00 M NaOH Initial T of both solutions: 16.9 C Maximum T recorded during reaction: 30.4 C Density of resulting NaCl solution: 1.04 g/mL c of 1.00 M NaCl(aq) 3.93 J/g K (b) Use the result from part (a) and the following data to determine H rxn for the reaction between zinc and HCl(aq): Amounts used: 100.0 mL of 1.00 M HCl and 1.3078 g of ZnInitial T of HCl solution and Zn: 16.8 C Maximum T recorded during reaction: 24.1 C Density of 1.0 M HCl solution 1.015 g/mL c of resulting ZnCl2(aq) 3.95 J/g K (c) Given the values below, what is the error in your experiment?

One mole of nitrogen gas confined within a cylinder by a piston is heated from 0 C to 819 C at 1.00 atm. (a) Calculate the work of expansion of the gas in joules (1 J 9.87 10 3 atm L). Assume all the energy is used to do work. (b) What would be the temperature change if the gas were heated with the same amount of energy in a container of fixed volume? (Assume the specific heat capacity of N2 is 1.00 J/g K.)

The chemistry of nitrogen oxides is very versatile. Given the following reactions and their standard enthalpy changes, (1) NO(g) NO2(g) N2O3(g) Hrxn ? ? 39.8 kJ (2) NO(g) NO2(g) O2(g) N2O5(g) Hrxn ? ? 112.5 kJ (3) 2NO2(g) N2O4(g) Hrxn ? ? 57.2 kJ (4) 2NO(g) O2(g) 2NO2(g) Hrxn ? ? 114.2 kJ (5) N2O5(s) N2O5(g) Hsubl 54.1 kJ calculate the heat of reaction for

Electric generating plants transport large amounts of hot water through metal pipes, and oxygen dissolved in the water can cause a major corrosion problem. Hydrazine (N2H4) added to the water avoids the problem by reacting with the oxygen: About 4 10 7 kg of hydrazine is produced every year by reacting ammonia with sodium hypochlorite in the Raschig process: 2NH3(aq) NaOCl(aq) N2H4(aq) NaCl(aq) H2O(l) H rxn ? ?151 kJ (a) If H f of NaOCl(aq) ? ? 346 kJ/mol, find H f of N2H4(aq). (b) What is the heat released when aqueous N2H4 is added to 5.00 10 3 L of plant water that is 2.50 10 4 M O2?

Liquid methanol (CH3OH) can be used as an alternative fuel in pickup and SUV engines. An industrial method for preparing it uses the catalytic hydrogenation of carbon monoxide: How much heat (in kJ) is released when 15.0 L of CO at 85 C and 112 kPa reacts with 18.5 L of H2 at 75 C and 744 torr?

(a) How much heat is released when 25.0 g of methane burns in excess O2 to form gaseous CO2 and H2O? (b) Calculate the temperature of the product mixture if the methane and air are both at an initial temperature of 0.0 C. Assume a stoichiometric ratio of methane to oxygen from the air, with air being 21% O2 by volume (c of CO2 57.2 J/mol K; c of H2O(g) 36.0 J/mol K; c of N2 30.5 J/mol K).