Two aircraft rivets, one iron and the other copper, are placed in a calorimeter that has

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 used to accomplish each 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 208C. In summer, an air conditioner uses the same amount of electrical energy to cool the room to 208C. Is the change in internal energy of the heater larger, smaller, or the same as that of the air conditioner? Explain.

You lift your textbook and drop it onto a desk. Describe 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 from and delivers 425 J of work to its surroundings. What is the change in internal energy of the system (in J)?

A system releases 255 cal of heat to the surroundings and delivers 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 to gaseous carbon dioxide releases 6.631010 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 absorbs 9.03106 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 4.13103 Calories. Express this quantity of energy in joules and kilojoules.

If an athlete expends 1950 kJ/h, how long does it take her 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 often more convenient to measure DH than DE?

Hot packs used by skiers use the crystallization of sodium acetate from a concentrated solution. What is the sign of DH 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 DH is less than (more negative), equal to, or greater than DE of the system. Explain. (a) An ideal gas is cooled at constant pressure. (b) A gas mixture reacts exothermically at fixed volume. (c) A solid reacts exothermically to yield a mixture of gases in a container of variable volume.

At constant temperature, a sample of helium gas expands from 922 mL to 1.14 L against a pressure of 2.33 atm. Find w (in J) done by the gas (1 J 5 9.8731023 atmL).

The external pressure on a gas sample is 2660 mmHg, and the volume changes from 0.88 L to 0.63 L at constant temperature. Find w (in kJ) done on the gas (1 atmL 5 101.3 J).

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

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

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

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

Write a balanced equation and draw an approximate enthalpy diagram for (a) combustion of 1 mol of liquid methanol (CH3OH); (b) formation of 1 mol of NO2 from its elements (heat is absorbed).

Write a balanced equation and draw an approximate enthalpy diagram for (a) sublimation of dry ice [conversion of CO2(s) directly to CO2(g)]; (b) reaction of 1 mol of SO2 with O2.

The circles represent a phase change at constant temperature: Is the value of each of the following positive (1), negative (2), or zero: (a) qsys; (b) DEsys; (c) DEuniv?

The scenes below represent a physical change taking place in a piston-cylinder assembly: 1.05 atm 1.05 atm (a) Is wsys 1, 2, or 0? (b) Is DHsys 1, 2, or 0? (c) Can you determine whether DEsurr is 1, 2, or 0? Explain.

Which is larger, the specific heat capacity or the molar heat capacity of a substance? Explain.

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, molar heat capacity, and heat capacity.

Both a coffee-cup calorimeter and a bomb calorimeter can be used to measure the heat transferred in a reaction. Which measures DE and which measures DH? Explain.

Find q when 22.0 g of water is heated from 25.08C to 100.8C. 6.38 Calculate q when 0.10 g of ice is cooled from 10.8C to 2758C (cice 5 2.087 J/g?K).

Calculate q when 0.10 g of ice is cooled from 10.8C to 2758C (cice 5 2.087 J/g?K).

A 295-g aluminum engine part at an initial temperature of 13.008C absorbs 75.0 kJ of heat. What is the final temperature of the part (c of Al 5 0.900 J/g?K)?

A 27.7-g sample of the radiator coolant ethylene glycol releases 688 J of heat. What was the initial temperature of the sample if the final temperature is 32.58C (c of ethylene glycol 5 2.42 J/g?K)?

Two iron bolts of equal massone at 100.8C, the other at 558Care placed in an insulated container. Assuming the heatcapacity of the container is negligible, what is the final temperature inside the container (c of iron 5 0.450 J/g?K)?

One piece of copper jewelry at 1058C has twice the mass of another piece at 458C. Both are placed in a calorimeter of negligible heat capacity. What is the final temperature inside the calorimeter (c of copper 5 0.387 J/g?K)?

When 155 mL of water at 268C is mixed with 75 mL of water at 858C, what is the final temperature? (Assume that no heat is released to the surroundings; d of water 5 1.00 g/mL.)

An unknown volume of water at 18.28C is added to 24.4 mL of water at 35.08C. If the final temperature is 23.58C, what was the unknown volume? (Assume that no heat is released to the surroundings; d of water 5 1.00 g/mL.)

A 455-g piece of copper tubing is heated to 89.58C and placed in an insulated vessel containing 159 g of water at 22.88C. Assuming no loss of water and a heat capacity of 10.0 J/K for the vessel, what is the final temperature (c of copper 5 0.387 J/g?K)?

A 30.5-g sample of an alloy at 93.08C is placed into 50.0 g of water at 22.08C in an insulated coffee cup with a heat capacity of 9.2 J/K. If the final temperature of the system is 31.18C, what is the specific heat capacity of the alloy?

High-purity benzoic acid (C6H5COOH; DH for combustion 5 23227 kJ/mol) is used to calibrate bomb calorimeters. A 1.221-g sample burns in a calorimeter (heat capacity of 1365 J/8C) that contains 1.200 kg of water. What is the temperature change?

Two aircraft rivets, one iron and the other copper, are placed in a calorimeter that has an initial temperature of 20.8C. The data for the rivets are as follows: Iron Copper Mass (g) 30.0 20.0 Initial T (8C) 0.0 100.0 c (J/g?K) 0.450 0.387 (a) Will heat flow from Fe to Cu or from Cu to Fe? (b) What other information is needed to correct any measurements 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 placed 1.520 g of a hydrocarbon in the bomb of a calorimeter (see Figure 6.10, p. 265). The bomb was immersed in 2.550 L of water and the sample was burned. The water temperature rose from 20.008C to 23.558C. If the calorimeter (excluding the water) had a heat capacity of 403 J/K, what was the heat released (qV) per gram of hydrocarbon?

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 23.508C, the temperature rises to 30.178C. Calculate DH of this reaction. (Assume that the total volume is the sum of the volumes and that the density and specific heat capacity of the solution are the same as for water.)

Does a negative DH mean that the heat should be treated as a reactant or as a product?

Would you expect O2(g) - 2O(g) to have a positive or a negative DH? Explain.

Is DH positive or negative when 1 mol of water vapor condenses to liquid water? Why? How does this value compare with DH 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: 1 8S8(s) 1 H2(g) - H2S(g) DH 5 220.2 kJ (a) Is this an exothermic or endothermic reaction? (b) What is DH for the reverse reaction? (c) What is DH when 2.6 mol of S8 reacts? (d) What is DH when 25.0 g of S8 reacts?

Consider the following balanced thermochemical equation for the decomposition of the mineral magnesite: MgCO3(s) - MgO(s) 1 CO2(g) DH 5 117.3 kJ (a) Is heat absorbed or released in the reaction? (b) What is DH for the reverse reaction? (c) What is DH when 5.35 mol of CO2 reacts with excess MgO? (d) What is DH 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. (b) What is DH when 3.50 g of NO decomposes to its elements? 6.57 When 1 mol of KBr(s) decomposes to its elements, 394 kJ of heat is absorbed. (a) Write a balanced thermochemical equation. (b) What is DH when 10.0 kg of KBr forms from its elements?

When 1 mol of KBr(s) decomposes to its elements, 394 kJ of heat is absorbed. (a) Write a balanced thermochemical equation. (b) What is DH 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: 2H2O2(l) - 2H2O(l) 1 O2(g) DH 5 2196.1 kJ 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 reactivity. With the more reactive halogens, for example, diborane (B2H6) forms trihalides even at low temperatures: B2H6(g) 1 6Cl2(g) - 2BCl3(g) 1 6HCl(g) DH 5 2755.4 kJ What is DH per kilogram of diborane that reacts?

Deterioration of buildings, bridges, and other structures through the rusting of iron costs millions of dollars a day. The actual process requires water, but a simplified equation is 4Fe(s) 1 3O2(g) - 2Fe2O3(s) DH 5 21.653103 kJ (a) How much heat is released when 0.250 kg of iron rusts? (b) How much rust forms when 4.853103 kJ of heat is released?

A mercury mirror forms inside a test tube as a result of the thermal decomposition of mercury(II) oxide: 2HgO(s) - 2Hg(l) 1 O2(g) DH 5 181.6 kJ (a) How much heat is absorbed to decompose 555 g of the oxide? (b) If 275 kJ of heat is absorbed, how many grams of Hg form?

Most ethylene (C2H4), the starting material for producing polyethylene, comes from petroleum processing. It also occurs naturally as a fruit-ripening hormone and as a component of natural gas. (a) The heat transferred during combustion of C2H4 is 21411 kJ/mol. Write a balanced thermochemical equation. (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 produces CO2(g) and H2O(g) and releases 5.643103 kJ/mol of sucrose. (a) Write a balanced thermochemical equation for the overall process. (b) How much heat is released per gram of sucrose oxidized?

Express Hesss law in your own words.

What is the main application of Hesss law?

When carbon burns in a deficiency of O2, a mixture of CO and CO2 forms. Carbon burns in excess O2 to form only CO2, and CO burns in excess O2 to form only CO2. Use DH values of the latter two reactions (from Appendix B) to calculate DH for C(graphite) 1 1 2O2(g) - CO(g)

Calculate DH for Ca(s) 1 1 2O2(g) 1 CO2(g) - CaCO3(s) given the following reactions: Ca(s) 1 1 2O2(g) - CaO(s) DH 5 2635.1 kJ CaCO3(s) - CaO(s) 1 CO2(g) DH 5 178.3 kJ

Calculate DH for 2NOCl(g) - N2(g) 1 O2(g) 1 Cl2(g) given the following reactions: 1 2N2(g) 1 1 2O2(g) - NO(g) DH 5 90.3 kJ NO(g) 1 1 2Cl2(g) - NOCl(g) DH 5 238.6 kJ

Write the balanced overall equation (equation 3) for the following process, calculate DHoverall, and match the number of each equation with the letter of the appropriate arrow in Figure P6.69: (1) N2(g) 1 O2(g) - 2NO(g) DH 5 2180.6 kJ (2) 2NO(g) 1 O2(g) - 2NO2(g) DH 5 2114.2 kJ (3) DHoverall 5 ?

Write the balanced overall equation (equation 3) for the following process, calculate DHoverall, and match the number of each equation with the letter of the appropriate arrow in Figure P6.70: (1) P4(s) 1 6Cl2(g) - 4PCl3(g) DH 5 21148 kJ (2) 4PCl3(g) 1 4Cl2(g) - 4PCl5(g) DH 5 12460 kJ (3) DHoverall 5 ? Figure P6.70

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

When 1 mol of CS2(l) forms from its elements at 1 atm and 258C, 89.7 kJ of heat 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 258C, diamond changes to graphite so slowly that the enthalpy change of the process must be obtained indirectly. Using equations from the numbered list below, determine DH for C(diamond) - C(graphite) (1) C(diamond) 1 O2(g) - CO2(g) DH 5 2395.4 kJ (2) 2CO2(g) - 2CO(g) 1 O2(g) DH 5 566.0 kJ (3) C(graphite) 1 O2(g) - CO2(g) DH 5 2393.5 kJ (4) 2CO(g) - C(graphite) 1 CO2(g) DH 5 2172.5 kJ

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

How are DH8 f values used to calculate DH8 rxn?

Make any changes needed in each of the following equations to make the enthalpy change equal to DH8 f for the compound: (a) Cl(g) 1 Na(s) - NaCl(s) (b) H2O(g) - 2H(g) 1 1 2O2(g) (c) 1 2N2(g) 1 3 2H2(g) - NH3(g)

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 DH8 rxn for each of the following: (a) 2H2S(g) 1 3O2(g) - 2SO2(g) 1 2H2O(g) (b) CH4(g) 1 Cl2(g) - CCl4(l) 1 HCl(g) 3unbalanced4

Calculate DH8 rxn for each of the following: (a) SiO2(s) 1 4HF(g) - SiF4(g) 1 2H2O(l) (b) C2H6(g) 1 O2(g) - CO2(g) 1 H2O(g) 3unbalanced4

Copper(I) oxide can be oxidized to copper(II) oxide: Cu2O(s) 1 1 2O2(g) - 2CuO(s) DH8rxn 5 2146.0 kJ Given DH8 f of Cu2O(s) 5 2168.6 kJ/mol, find DH8 f of CuO(s).

Acetylene burns in air by the following equation: C2H2(g) 1 5 2O2(g) - 2CO2(g) 1 H2O(g) DH8rxn 5 21255.8 kJ Given DH8 f of CO2(g) 5 2393.5 kJ/mol and DH8 f of H2O(g) 5 2241.8 kJ/mol, find DH8 f of C2H2(g).

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 2PbSO4(s) 1 2H2O(l) - Pb(s) 1 PbO2(s) 1 2H2SO4(l) (a) Use DH8 f values from Appendix B to calculate DH8 rxn. (b) Use the following equations to check your answer to part (a): (1) Pb(s) 1 PbO2(s) 1 2SO3(g) - 2PbSO4(s) DHrxn 8 5 2768 kJ (2) SO3(g) 1 H2O(l) - H2SO4(l) DHrxn 8 5 2132 kJ

Stearic acid (C18H36O2) is a 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, you are ingesting some fats containing stearic acid. (a) Write a balanced equation for the combustion of stearic acid to gaseous products. (b) Calculate DH8rxn for this combustion (DH8 f of C18H36O2 5 2948 kJ/mol). (c) Calculate the heat (q) released in kJ and kcal when 1.00 g of stearic acid is burned completely. (d) A candy bar contains 11.0 g of fat and provides 100. Cal from fat; is this consistent with your answer for part (c)?

Diluting sulfuric acid with water is highly exothermic: H2SO4(l) - H2O H2SO4(aq) 1 heat (a) Use Appendix B to find DH8rxn for diluting 1.00 mol of H2SO4(l) (d 5 1.83 g/mL) to 1 L of 1.00 M H2SO4(aq) (d 5 1.060 g/mL). (b) Suppose you carry out the dilution in a calorimeter. The initial T is 25.08C, 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 begins a trip in a helium-filled balloon in early morning when the temperature is 158C. By mid-afternoon, the temperature is 30.8C. Assuming the pressure remains at 1.00 atm, for each mole of helium, calculate the following: (a) The initial and final volumes (b) The change in internal energy, DE (Hint: Helium behaves like an ideal gas, so E 5 3 2 nRT. 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) DH for the process (in J) (f) Explain the relationship between the answers to parts (d) and (e).

In winemaking, the sugars in grapes undergo fermentation by yeast to yield CH3CH2OH and CO2. During cellular respiration (combustion), sugar and ethanol yield water vapor and CO2. (a) Using C6H12O6 for sugar, calculate DH8 rxn of fermentation and of respiration. (b) Write a combustion reaction for ethanol. Which has a higher DH8rxn 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 DH8rxn of each reaction (DH8 f of C21H44 5 2476 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 5.00% by mass of it 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: H2C O CH2(g) CH4(g) + CO(g) Liquid EO has DH8 f 5 277.4 kJ/mol and DH8 for its vaporization 5 569.4 J/g. (a) Calculate DH8 rxn for the gas-phase reaction. (b) External heating causes the vapor to decompose at 10 bar and 938C in a distillation column. What is the final temperature if the average specific heat capacity of the products is 2.5 J/g?8C?

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 DH8 rxn. (b) If each molecule of product represents 1.5031022 mol, what quantity of heat (in J) is released or absorbed?

Isooctane (C8H18; d 5 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 combustion of 20.4 gal of isooctane to gases (DH8rxn 5 25.443103 kJ/mol)? (b) The energy delivered to the wheels at 65 mph is 5.53104 kJ/h. Assuming all the energy is transferred as work to the wheels, how far (in km) can the car travel on the 20.4 gal of fuel? (c) If the actual range is 455 mi, explain your answer to (b).

Four 50.-g samples of different colorless liquids are placed in beakers at Tinitial 5 25.008C. Each liquid is heated until 450. J of heat has been absorbed; Tfinal is shown on each beaker below. Rank the liquids in order of increasing specific heat capacity. A B C D 27.15C 35.59C 28.96C 30.29C

Reaction of gaseous ClF with F2 yields liquid ClF3, an important fluorinating agent. Use the following thermochemical equations to calculate DH8 rxn for this reaction: (1) 2ClF(g) 1 O2(g) - Cl2O(g) 1 OF2(g) DHrxn 8 5 167.5 kJ (2) 2F2(g) 1 O2(g) - 2OF2(g) DHrxn 8 5 243.5 kJ (3) 2ClF3(l) 1 2O2(g) - Cl2O(g) 1 3OF2(g) DHrxn 8 5 394.1 kJ

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 258C, what mass of AgI forms? (b) Use Appendix B to find DH8rxn. (c) What is DTsoln (assuming the volumes are additive and the solution has the density and specific heat capacity of water)?

The calorie (4.184 J) is defined as the quantity of energy needed to raise the temperature of 1.00 g of liquid water by 1.008C. The British thermal unit (Btu) is defined as the quantity of energy needed to raise the temperature of 1.00 lb of liquid water by 1.008F. (a) How many joules are in 1.00 Btu (1 lb 5 453.6 g; 1.08C 5 1.88F)? (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 that water forms as a gas.) (d) If natural gas costs $0.66 per therm, what is the cost per mole of methane? (Assume that natural gas is pure methane.) (e) How much would it cost to warm 318 gal of water in a hot tub from 15.08C to 42.08C by burning methane (1 gal 5 3.78 L)?

When organic matter decomposes 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 deposits of natural gas can produce 5600 EJ of energy (1 EJ 5 1018 J). Current total global energy usage is 4.03102 EJ per year. Find the mass (in kg) of known deposits of natural gas (DH8 rxn for the combustion of CH4 5 2802 kJ/mol). (b) At current rates of usage, for how many years could these deposits 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 25.08C to 100.08C (d of H2O 5 1.00 g/mL; d of CH4 at STP 5 0.72 g/L)? (d) The fission of 1 mol of uranium (about 431024 ft3) in a nuclear reactor produces 231013 J. What volume (in ft3) of natural gas would produce the same amount of energy?

A reaction takes place in a steel vessel within a chamber filled with argon gas. Shown below are atomic-scale views of the argon adjacent to the surface of the container wall of the reaction vessel before and after the reaction. Was the reaction exothermic or endothermic? Explain. Before reaction Reaction mixture Container wall After reaction

An aqueous waste stream with a maximum concentration of 0.50 M H2SO4 (d 5 1.030 g/mL at 258C) is neutralized by controlled addition of 40% NaOH (d 5 1.430 g/L) before it goes to the process sewer and then to the chemical plant waste treatment facility. 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 40.8C. The maximum temperature reached by the NaOH solution and the waste stream is 318C. Could the temperature increase due to the heat transferred by the neutralization cause the organic vapor to explode? Assume that 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 DH8rxn 5 21.503104 kJ for the combustion equation as written in part (a), determine DH8 f of kerosene. (c) Calculate the heat released by combustion of 0.50 gal of kerosene (d of kerosene 5 0.749 g/mL). (d) How many gallons of kerosene must be burned for a kerosene furnace to produce 1250. Btu (1 Btu 5 1.055 kJ)?

Silicon tetrachloride is produced annually on the multikiloton scale and used in making transistor-grade silicon. It can be produced 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) Si(s) 1 2Cl2(g) - SiCl4(g) (2) SiO2(s) 1 2C(graphite) 1 2Cl2(g) - SiCl4(g) 1 2CO(g) (3) SiCl4(g) 1 2H2O(g) - SiO2(s) 1 4HCl(g) DH8rxn 5 2139.5 kJ (a) Use reaction 3 to calculate the standard enthalpies of reaction of reactions 1 and 2. (b) What is the standard enthalpy of reaction for a fourth reaction that is the sum of reactions 2 and 3?

One mole of nitrogen gas confined within a cylinder by a piston is heated from 08C to 8198C at 1.00 atm. (a) Calculate the work done by the expanding gas in joules (1 J 5 9.8731023 atm?L). Assume that all the energy is used to do work. (b) What would be the temperature change if the gas were heated using the same amount of energy in a container of fixed volume? (Assume that 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) 1 NO2(g) - N2O3(g) DH8 rxn 5 239.8 kJ (2) NO(g) 1 NO2(g) 1 O2(g) - N2O5(g) DH8 rxn 5 2112.5 kJ (3) 2NO2(g) - N2O4(g) DH8 rxn 5 257.2 kJ (4) 2NO(g) 1 O2(g) - 2NO2(g) DH8 rxn 5 2114.2 kJ (5) N2O5(s) - N2O5(g) DH8 rxn 5 54.1 kJ calculate the standard enthalpy of reaction for N2O3(g) 1 N2O5(s) - 2N2O4(g)

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: N2H4(aq) 1 O2(g) - N2(g) 1 2H2O(l) About 43107 kg of hydrazine is produced every year by reacting ammonia with sodium hypochlorite in the Raschig process: 2NH3(aq) 1 NaOCl(aq) - N2H4(aq) 1 NaCl(aq) 1 H2O(l) DH8 rxn 5 2151 kJ (a) If DH8 f of NaOCl(aq) 5 2346 kJ/mol, find DH8 f of N2H4(aq). (b) What is the heat released when aqueous N2H4 is added to 5.003103 L of water that is 2.5031024 M O2?

Liquid methanol (CH3OH) can be used as an alternative fuel in pickup and SUV engines. An industrial method for preparing it involves the catalytic hydrogenation of carbon monoxide: CO(g) 1 2H2(g) -- catalyst CH3OH(l) How much heat (in kJ) is released when 15.0 L of CO at 858C and 112 kPa reacts with 18.5 L of H2 at 758C 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 0.08C. Assume a stoichiometric ratio of methane to oxygen from the air, with air being 21% O2 by volume (c of CO2 5 57.2 J/mol?K; c of H2O(g) 5 36.0 J/mol?K; c of N2 5 30.5 J/mol?K).