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chemistry for engineering students

Questions and Answers of Chemistry For Engineering Students

Calculate (a) q when a system does 54 J of work and its energy decreases by 72 J and (b) ΔE for a gas that releases 38 J of heat and has 102 J of work done on it.
If the algebraic sign of ΔE is negative, in which direction has energy flowed?
State the first law of thermodynamics briefly in your own words.
PV-work occurs when volume changes and pressure remains constant. If volume is held constant, can PV-work be done? What happens to Equation 9.2 when volume is held constant?Equation 9.2 ΔΕ = q + w
Which type of energy, heat or work, is valued more by society? What evidence supports your judgment?
Which system does more work: (a) ΔE = – 2436 J, q = 400 J; or (b) ΔE = 317 J, q = 347 J?
In which case is heat added to the system: (a) ΔE = –43 J, w = 40 J; or (b) ΔE = 31 J, w = 34 J?
Modern appliances are significantly more energy efficient than those of a generation ago, and this trend is expected to continue. Will these efficiency gains necessarily lead to reduced household
Gas furnaces have achieved impressive efficiency levels largely through the addition of a second heat exchanger that condenses water vapor that would otherwise escape out the exhaust system attached
When energy conservation programs are promoted, they sometimes include strategies such as turning out lights. Use the web to determine the average percentage of U.S. household energy usage that is
When an electrical appliance whose power usage is X watts is run for Y seconds, it uses X × Y joules of energy. The energy unit used by electrical utilities in their monthly bills is the
Define the term calorimetry.
For the example of shallow water and sandy beaches, which material has a larger heat capacity or specific heat? How does a hot day at the beach provide evidence for your answer?
A metal radiator is made from 26.0 kg of iron. The specific heat of iron is 0.449 J g-1 8C-1. How much heat must be supplied to the radiator t3.50 × 105 Jo raise its temperature from 25.0 to 55.08C?
The material typically used to heat metal radiators is water. If a boiler generates water at 79.58C, what mass of water was needed to provide the heat required in the previous problem? Water has a
Copper wires used to transport electrical current heat up because of the resistance of the wire. If a 140-g wire gains 280 J of heat, what is the change in temperature in the wire? Copper has a
A copper nail and an iron nail of the same mass and initially at the same room temperature are both put into a vessel containing boiling water. Which one would you expect to reach 100°C first? Why?
Define the term calibration.
A calorimeter contained 75.0 g of water at 16.95°C. A 93.3-g sample of iron at 65.58°C was placed in it, giving a final temperature of 19.68°C for the system. Calculate the heat capacity of the
The energy densities of various types of coal are listed below: Anthracite 35 kJ/g Subbituminous 31 kJ/g Bituminous 28 kJ/g Lignite 26 kJ/g An unknown sample of one of these coals is burned in an
How much thermal energy is required to heat all of the water in a swimming pool by 1ºC if the dimensions are 4 ft deep by 20 ft wide by 75 ft long? Report your result in megajoules.
How does the specific heat of water explain why cities on the coast of large bodies of water tend to be cooler in the summer than cities several miles inland?
Under what conditions does the enthalpy change equal the heat of a process?
Why is enthalpy generally more useful than internal energy in the thermodynamics of real world systems?
Define the terms exothermic and endothermic.
List at least two phase changes that are exothermic processes.
What happens to the temperature of a material as it undergoes an endothermic phase change? If heat is added, how can the temperature behave in this manner?
The heat of fusion of pure silicon is 43.4 kJ/mol. How much energy would be needed to melt a 5.24-g sample of silicon at its melting point of 1693 K?
If 14.8 kJ of heat is given off when 1.6 g of HCl condenses from vapor to liquid, what is ΔHcond for this substance?
When a 13.0-g sample of NaOH(s) dissolves in 400.0 mL of water in a coffee cup calorimeter, the temperature of the water changes from 22.68C to 30.78C. Assuming that the specific heat capacity of the
Calculate the energy required to convert 1.70 g of ice originally at –12.0°C into steam at 105°C.
Define the term formation reaction.
Write the formation reaction for each of the following substances.(a) CH4(g), (b) C3H8(ℓ), (c) HCl(g), (d) C6H12O6(s), (e) NaF(s)
Using these reactions, find the standard enthalpy change for the formation of 1 mol of PbO(s) from lead metal and oxygen gas.PbO(s) + C(graphite) → Pb(s) + CO(g) ΔH° = 106.8 kJ2 C(graphite) +
The phase change between graphite and diamond is difficult to observe directly. Both substances can be burned, however. From these equations, calculate ΔH° for the conversion of diamond into
The heat of combustion of butane is 22877 kJ/mol. Use this value to find the heat of formation of butane. (You may also need to use additional thermochemical data found in Appendix E.)Data from
Hydrogen gas will react with either acetylene or ethylene gas. The thermochemical equations for these reactions are provided below. Write the thermochemical equation for the conversion of acetylene
Using heats of formation tabulated in Appendix E, calculate the heats of reaction for the following.(a) C2H2(g)+ 5/2 O2(g) → 2 CO2(g) + H2O(ℓ)(b) PCl3(g) + Cl2(g) → PCl5(g)(c) C2H4(g) + H2O(g)
For the reaction C2H2(g) + 2 H2(g) → C2H6, ΔH° = –136 kJ. What are the ratios that can be defined between moles of substances and energy?
For the reaction N2(g) + O2(g) → 2 NO(g), ΔH° = 180.5 kJ.How much energy is needed to generate 35 moles of NO(g)?
Nitroglycerine, C3H5(NO3)3(ℓ), is an explosive most often used in mine or quarry blasting. It is a powerful explosive because four gases (N2, O2, CO2, and steam) are formed when nitroglycerine is
Silane, SiH4, burns according to the reaction, SiH4 + 2 O2 → SiO2 + 2 H2O, with ΔH° = –1429 kJ. How much energy is released if 15.7 g of silane is burned?
Sulfur trioxide can be removed from the exhaust gases of power plants by reaction with lime. The relevant reaction is CaO(s) + SO3(g) → CaSO4(s), with ΔH° = –886 kJ. If 240 kg of SO3 is to be
Reactions of hydrocarbons are often studied in the petroleum industry. One example is 2 C3H8(g) → C6H6(ℓ) + 5 H2(g), with ΔH° = 698 kJ. If 35 L of propane at 258C and 0.97 atm is to be reacted,
In principle, ozone could be consumed in a reaction with lead and carbon with the thermochemical equation Pb(s) + C(s) + O3(g) → PbCO3(s) ΔH° = –841.0 kJ. How much energy would be released if
When 0.0157 g of a compound with a heat of combustion of 237.6 kJ/mol is burned in a calorimeter, 18.5 J of heat is released. What is the molar mass of the compound?
Define the term energy density.
Why is energy density so important in the transportation of fuels?
What are some features of petroleum that make it such an attractive fuel?
How are the roles of transmission substations and distribution substations in the electrical grid similar? How are they different?
Residential electric service in the United States generally operates at 120 V, but transmission substations feed power onto the grid at 110 kV or higher. What advantage is realized by transmitting
In recent years, the notion of a “smart grid” has emerged. Do a web search and research the smart grid concept. How would the smart grid differ from the traditional grid?
Although it can be a nuisance when a laptop computer freezes up and needs to be rebooted, we accept that as somewhat inevitable. But clearly the need to occasionally reboot the control system for the
Without looking up any numerical data or doing calculations, predict whether the following enthalpy changes should be positive, negative, or zero.(a) ΔHf° for H2(g)(b) ΔHf° for O(g)(c) ΔHfusion
Without looking up any numerical data or doing calculations, predict whether the enthalpy change for each of the following reactions should be positive, negative, or zero.(a) H2O(ℓ) → H2O(s)(b)
Explain why each of the following chemical equations is not a correct formation reaction.(a) 4 Al(s) + 3 O2(g) → 2 Al2O3(s)(b) N2(g) +3/2 H2(g) → NH3(g)(c) 2 Na(s) + O(g) → Na2O(s)
When a reaction is exothermic, is the sum of bond energies of products or of reactants greater?
When a chemical bond breaks, is energy absorbed or released?
If you are designing a component that needs to be able to change temperature fairly quickly, should you use a material with a high or low specific heat? Explain your answer.
Use the concept that enthalpy is a state function to explain why, when a thermochemical equation is reversed, the magnitude of ΔH° stays the same but the sign changes.
The specific heat of gold is 0.13 J g-1 K-1 and that of copper is 0.39 J g-1 K-1. Suppose that we heat both a 25-g sample of gold and a 25-g sample of copper to 808C and then drop them into identical
A student performing a calorimetry experiment combined 100.0 mL of 0.50 M HCl and 100.0 mL of 0.50 M NaOH in a coffee cup calorimeter. Both solutions were initially at 20.08C, but when the two were
The figure below shows a “self-cooling” beverage can.The can is equipped with an outer jacket containing sodium carbonate (Na2CO3), which dissolves in water rapidly and endothermically:Na2CO3(s)
Some claim it would be more logical to use heats of atomization, the energy required to convert any molecule to its separated atoms, rather than heats of formation for doing calculations with
You make some iced tea by dropping 134 g of ice into 500.0 mL of warm tea in an insulated pitcher. If the tea is initially at 20.0°C and the ice cubes are initially at 0.0°C, how many grams of ice
Chemical engineers often must include ways to dissipate energy in the form of heat in their designs. What does this fact say about the enthalpy change of chemical reactions that are being used?
Many engineering designs must incorporate ways to dissipate energy in the form of heat. Water evaporators are common for this task. (a) What property of water makes it a good material for
The curing of concrete liberates energy as heat. (a) What does this observation suggest happens in terms of chemical bonds as concrete cures? (b) What type of strategies might a civil engineer
Price spikes in gasoline in 2008 led to renewed interest in coal gasification projects, in which coal is converted to gasoline. Looking at the relative energy density of gasoline and coal in Table
An engineer is designing a product in which a copper wire will carry large amounts of electricity. The resistive heating of a 65-g copper wire is expected to add 580 J of heat energy during a
Most first aid “cold packs” are based on the endothermic dissolution of ammonium nitrate in water:A particular cold pack contains 50.0 g of NH4NO3 and 125.0 g of water. When the pack is squeezed,
How much heat is required to convert 250 g of water from liquid at 23°C into steam at 107°C? (The necessary heat capacities and enthalpy changes can be found in the chapter or online.)
Hydrogen combines with oxygen in fuel cells according to the thermochemical equationSuppose that you are working with a firm that is using hydrogen fuel cells to power satellites. The satellite
Suppose that the working fluid inside an industrial refrigerator absorbs 680 J of energy for every gram of material that vaporizes in the evaporator. The refrigerator unit uses this energy flow as
The chemical reaction BBr3(g) + BCl3(g) → BBr2Cl(g) + BCl2Br(g), has an enthalpy change very close to zero. Using Lewis structures of the molecules, all of which have a central boron atom, provide
Two baking sheets are made of different metals. You purchase both and bake a dozen cookies on each sheet at the same time in your oven. You observe that after 9 minutes, the cookies on one sheet are
Silicon nitride, Si3N4, has physical, chemical, and mechanical properties that make it a useful industrial material. For a particular engineering project, it is crucial that you know the heat of
One reason why the energy density of a fuel is important is that to move a vehicle one must also move its unburned fuel. Octane is a major component of gasoline. It burns according to the
A runner generates 418 kJ of energy per kilometer from the cellular oxidation of food. The runner’s body must dissipate this heat or the body will overheat. Suppose that sweat evaporation is the
An engineer is using sodium metal as a cooling agent in a design because it has useful thermal properties. Looking up the heat capacity, the engineer finds a value of 28.2 J mol–1 °C–1.
In passive solar heating, the goal is to absorb heat from the sun during the day and release it during the night. Which material would be better for this application: one with a high heat capacity or
A 1.0-kg sample of stainless steel is heated to 4008C. Suppose that you drop this hot sample into an insulated bucket that contains water at some known initial temperature. Assuming that there is no
At the beginning of 2016, the United States had 32.3 billion barrels of proven oil reserves. One barrel of oil can produce about 19.5 gallons of gasoline. Assume that the gallon of gasoline is pure
For a car weighing 980 kg, how much work must be done to move the car 24 miles? Ignore factors such as frictional loss and assume an average acceleration of 2.3 m/s2.
Suppose that the car in the previous problem has a fuel efficiency of 24 mpg. How much energy is released in burning a gallon of gasoline (assuming that all of it is octane)? Based on this
Suppose that there is 2.43 mol of nitrogen gas in an insulated, sealed 31.7-L container initially at 285k. The specific heat of nitrogen gas is 1.04 kJ kg-1 K-1 (note units). If a 5.44-kg block of
Calcium phosphate is an important precursor for the formation of bioceramic coatings. Draw the Lewis structure of the phosphate ion, PO4 3–.Strategy Follow the steps of the Lewis structure
Poly(vinyl alcohol) is used in several biomaterials applications, including surgical sutures. It is also used in drops for dry eyes and some contact lens solutions. Draw the Lewis structure of vinyl
Determine the shape of the following molecules using VSEPR theory.(a) SF4, (b) BrF5Strategy As always, we start by drawing the Lewis structures. Then count the number of electron pairs around the
Although much less common than silicon devices, germanium-based semiconductors can also be fabricated. Which kind of material (n- or p-type) would result if pure germanium were doped with (a)
Which type of intermolecular forces need to be overcome to convert each of the following from a liquid to a gas? (a) CH4, (b) CH3F, (c) CH3OH Strategy Dispersion forces will exist for any
Each of the following monomers or pairs of monomers can undergo condensation polymerization reactions. Draw the structures showing the repeat units and linkages in each of the resulting polymers.(a)
If 515 J of heat is added to a gas that does 218 J of work as a result, what is the change in the energy of the system?Strategy Energy flow occurs as either heat or work, and Equation 9.2 relates
The molar heat capacity of liquid water is 75.3 J mol-1 K-1. If 37.5 g of water is cooled from 42.0 to 7.08C, what is q for the water?Strategy The heat flow is proportional to the amount of water and
Calculate the enthalpy change when 245 g of ice melts.Strategy The ΔHfus value in Table 9.3 is in J/mol, so the amount of ice must be converted into moles. Multiplying the number of moles by ΔHfus
Sulfur trioxide reacts with water to form sulfuric acid, a major contributor to acid rain. One origin of SO3 is the combustion of sulfur, which is present in small quantities in coal, according to
Use tabulated data to find the heat of combustion of 1 mole of propane, C3H8, to form gaseous carbon dioxide and liquid water.Strategy We will need values for the heats of formation of the reactants
Ethanol, C2H5OH, is used to introduce oxygen into some blends of gasoline. It has a heat of combustion of 1366.8 kJ/mol. What is the heat of formation of ethanol?Strategy We know the relationship
An engine generates 15.7 g of nitric oxide gas during a laboratory test. How much heat was absorbed in producing this NO?Strategy The thermochemical equation for this reaction was given earlier. This
Report the result for the indicated arithmetic operations using the correct number of significant figures. Assume that all values are measurements.(a) 4.30 × 0.31 (b) 4.033 + 88.1 (c) 5.6/1.732 ×

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