Chemistry: Structure and Properties (2nd Edition)
2nd Edition
ISBN: 9780134293936
Author: Nivaldo J. Tro
Publisher: PEARSON
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Textbook Question
Chapter 9, Problem 141E
Which statement is true of an endothermic reaction?
- Strong bonds break and weak bonds form.
- Weak bonds break and strong bonds form.
- The bonds that break and those that form are of approximately the same strength.
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8) In an exothermic reaction, the enthalpy of the reaction can be calculated by
a. Subtracting the sum of all the bond energies of the
products from the sum of all the bond energies of the
reactants.
b. Subtracting the sum of all the bond energies of the reactants
from the sum of all the bond energies of the products
c. Finding the sum of the enthalpies of formation of all the
products and reactants together d. All of the above
During chemical reactions the bonds between atoms break and new bonds form. Energy must be absorbed to break a bond, so breaking bonds is endothermic. Making new bonds is exothermic because energy is released. If the reaction equation is:
2H (g) -> H2 (g)
Is this reaction exothermic or endothermic? Use ideas about bonds to explain why.
In chemical reactions, heat is converted into chemical energy (the potential energy stored
in chemical bonds) or vice versa. Bond energy is the energy required to break one mole of
the bond in the gas phase. Since it takes energy to break a bond, bond energies are
always positive. Conversely, energy is released when bonds are formed. Thus, the
enthalpy change for a reaction can be approximated from
Part A
Calculate the bond energy per mole for breaking all the bonds in methane, CH4.
ΔΗ
Σ(ΔΗ breaking) + Σ(ΔΗ forming)
Express your answer to four significant figures and include the appropriate units.
where H represents bond energies for the breaking (positive bond energy) or forming
(negative bond energy) of a bond and Hrxn represents the overall enthalpy for the
• View Available Hint(s)
reaction.
Use the table to answer questions about bond energies.
HẢ
Bond energy
Bond
(kJ/mol )
Value
Units
AHCH, =
C-C
347
C=C
611
Submit
Сн
414
C-O
360
Part B
C=OinCO2
799
O-0
142
Calculate the bond…
Chapter 9 Solutions
Chemistry: Structure and Properties (2nd Edition)
Ch. 9 - What is thermochemistry? Why is it important?Ch. 9 - What is energy? What is work? List some examples...Ch. 9 - Prob. 3ECh. 9 - What is the law of conservation of energy? How...Ch. 9 - A friend claims to have constructed a machine that...Ch. 9 - What is a state function? List some examples of...Ch. 9 - What is internal energy? Is internal energy a...Ch. 9 - If energy flows out of a chemical system and into...Ch. 9 - If the internal energy of the products of a...Ch. 9 - What is heat? Explain the difference between heat...
Ch. 9 - How is the change in internal energy of a system...Ch. 9 - Explain how the sum of heat and work can be a...Ch. 9 - What is heat capacity? Explain the difference...Ch. 9 - Explain how the high specific heat capacity of...Ch. 9 - If two objects, A and B, of different temperature...Ch. 9 - What is pressure-volume work? How is it...Ch. 9 - What is calorimetry? Explain the difference...Ch. 9 - What is the change in enthalpy ( H) for a...Ch. 9 - Explain the difference between an exothermic and...Ch. 9 - From a molecular viewpoint where does the energy...Ch. 9 - From a molecular viewpoint, where does the energy...Ch. 9 - Is the change in enthalpy for a reaction an...Ch. 9 - Explain how the value of H for a reaction changes...Ch. 9 - What is Hess's law? Why is it useful?Ch. 9 - What is a standard state? What is the standard...Ch. 9 - How can bond energies be used to estimate H for a...Ch. 9 - Explain the difference between exothermic and...Ch. 9 - What is the standard enthalpy of formation for a...Ch. 9 - How do you calculate Hrxn from tabulated standard...Ch. 9 - What is lattice energy? 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Use average bond...Ch. 9 - Hydrogen, a potential future fuel, can be produced...Ch. 9 - Hydroxyl radicals react with and eliminate many...Ch. 9 - Write an equation for the formation of each...Ch. 9 - Prob. 82ECh. 9 - S3. Hydrazine (N2H4) is a fuel used by some...Ch. 9 - Prob. 84ECh. 9 - Prob. 85ECh. 9 - Prob. 86ECh. 9 - Prob. 87ECh. 9 - Prob. 88ECh. 9 - Top fuel dragsters and funny cars burn...Ch. 9 - Prob. 90ECh. 9 - Prob. 91ECh. 9 - Rubidium iodide has a lattice energy of-617...Ch. 9 - Prob. 93ECh. 9 - Prob. 94ECh. 9 - Use the Born-Haber cycle and data from Appendix...Ch. 9 - Prob. 96ECh. 9 - The kinetic energy of a rolling billiard ball is...Ch. 9 - A100-W light bulb is placed in a cylinder equipped...Ch. 9 - Evaporating sweat cools the body because...Ch. 9 - LP gas burns according to the exothermic reaction:...Ch. 9 - Use standard enthalpies of formation to calculate...Ch. 9 - Dry ice is solid carbon dioxide. Instead of...Ch. 9 - A 25.5-g aluminum block is warmed to 65.4 °C and...Ch. 9 - We mix 50.0 mL of ethanol (density = 0.789 g/mL)...Ch. 9 - Prob. 105ECh. 9 - Prob. 106ECh. 9 - One tablespoon of peanut butter has a mass of 16...Ch. 9 - Prob. 108ECh. 9 - Prob. 109ECh. 9 - When we burn 10.00 g of phosphorus in O2 (g) to...Ch. 9 - The H for the oxidation of S in the gas phase to...Ch. 9 - The Hfo of TiI3(s) is -328 kJ/mol; and the Ho for...Ch. 9 - A copper cube measuring 1.55 cm on edge and an...Ch. 9 - A pure gold ring and pure silver ring have a total...Ch. 9 - The reaction of Fe2O3(s) with Al(s) to form...Ch. 9 - Prob. 116ECh. 9 - Prob. 117ECh. 9 - Prob. 118ECh. 9 - Prob. 119ECh. 9 - Calculate the heat of atomization (see previous...Ch. 9 - Prob. 121ECh. 9 - Prob. 122ECh. 9 - Prob. 123ECh. 9 - Prob. 124ECh. 9 - Prob. 125ECh. 9 - Find H, E, q, and w for the freezing of water at...Ch. 9 - The heat of vaporization of water at 373 K is 40.7...Ch. 9 - Prob. 128ECh. 9 - Prob. 129ECh. 9 - Prob. 130ECh. 9 - Prob. 131ECh. 9 - Prob. 132ECh. 9 - Prob. 133ECh. 9 - Which expression describes the heat emitted in a...Ch. 9 - Prob. 135ECh. 9 - Prob. 136ECh. 9 - Prob. 137ECh. 9 - Prob. 138ECh. 9 - Prob. 139ECh. 9 - Which statement is true of a reaction in which V...Ch. 9 - Which statement is true of an endothermic...Ch. 9 - When a firecracker explodes, energy is obviously...Ch. 9 - Prob. 143ECh. 9 - Classify each process as endothermic or...Ch. 9 - A propane tank on a home barbeque contains 10.4 x...Ch. 9 - Prob. 146ECh. 9 - Consider the decomposition of liquid hydrogen...Ch. 9 - Prob. 148ECh. 9 - A chemical system produces 155 kJ of heat and does...Ch. 9 - Which sample is most likely to undergo the...Ch. 9 - Prob. 3SAQCh. 9 - A 12.5-g sample of granite initially at 82.0 C is...Ch. 9 - A cylinder with a moving piston expands from an...Ch. 9 - When a 3.80-g sample of liquid octane (C8H18)...Ch. 9 - Hydrogen gas reacts with oxygen to form water....Ch. 9 - Manganese reacts with hydrochloric acid to produce...Ch. 9 - Consider the reactions: A2BH1A3CH2 What is H for...Ch. 9 - Use standard enthalpies of formation to determine...Ch. 9 - Prob. 11SAQCh. 9 - Prob. 12SAQCh. 9 - Prob. 13SAQCh. 9 - Which set of compounds is arranged in order of...Ch. 9 - Prob. 15SAQ
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- When a reaction is exothermic, is the sum of bond energies of products or of reactants greater?arrow_forwardBond Enthalpy When atoms of the hypothetical element X are placed together, they rapidly undergo reaction to form the X2 molecule: X(g)+X(g)X2(g) a Would you predict that this reaction is exothermic or endothermic? Explain. b Is the bond enthalpy of X2 a positive or a negative quantity? Why? c Suppose H for the reaction is 500 kJ/mol. Estimate the bond enthalpy of the X2 molecule. d Another hypothetical molecular compound, Y2(g), has a bond enthalpy of 750 kJ/mol, and the molecular compound XY(g) has a bond enthalpy of 1500 kJ/mol. Using bond enthalpy information, calculate H for the following reaction. X2(g)+Y2(g)2XY(g) e Given the following information, as well as the information previously presented, predict whether or not the hypothetical ionic compound AX is likely to form. In this compound, A forms the A+ cation, and X forms the X anion. Be sure to justify your answer. Reaction: A(g)+12X2(g)AX(s)The first ionization energy of A(g) is 400 kJ/mol. The electron affinity of X(g) is 525 kJ/mol. The lattice energy of AX(s) is 100 kJ/mol. f If you predicted that no ionic compound would form from the reaction in Part e, what minimum amount of AX(s) lattice energy might lead to compound formation?arrow_forwardhat is the enthalpy change for a process? Is enthalpy a state function? In what experimental apparatus are enthalpy changes measured?arrow_forward
- Which statement(s) is/are true about bond enthalpy? (a) The bond energy for a triple bond between A and B is three times that of a single bond between A and B. (b) H for the breaking of a bond is always a negative number. (c) Energy is required to make a bond. (d) Bond enthalpy is defined only for bonds broken or formed in the gaseous state. (e) The presence of bonds does not influence the geometry of a molecule. However, the presence of bonds affects the value of the bond enthalpy between two atoms.arrow_forwardA commercial process for preparing ethanol (ethyl alcohol), C2H5OH, consists of passing ethylene gas. C2H4, and steam over an acid catalyst (to speed up the reaction). The gas-phase reaction is Use bond enthalpies (Table 9.5) to estimate the enthalpy change for this reaction when 37.0 g of ethyl alcohol is produced.arrow_forwardCompare your answers from parts a and b of Exercise 69 of Chapter 3 with H values calculated for each reaction using standard enthalpies of formation in Appendix 4. Do enthalpy changes calculated from bond energies give a reasonable estimate of the actual values?arrow_forward
- Write all resonance structures of chlorobenzene, C6H5Cl, a molecule with the same cyclic structure as benzene. In all structures, keep the CCl bond as a single bond. Which resonance structures are the most important?arrow_forwardhat does temperature measure? Are the molecules in a beaker of warm water moving at the same speed as the molecules in a beaker of cold water? Explain? What is heat? Is heat the same as temperature?arrow_forwardExplain the decomposition of nitroglycerin in terms of relative bond enthalpies.arrow_forward
- When a molecule can form two different structures, the structure with the stronger bonds is usually the more stable form. Use bond energies to predict the correct structure of the hydroxylamine molecule:arrow_forwardMethylcyanoacrylate is the active ingredient in super glues. Its Lewis structure is In this molecule, which is the (a) weakest carbon-containing bond? (b) strongest carbon-containing bond? (c) most polar bond?arrow_forwardCalculate the enthalpy of reaction for HCN(g)H(g)+C(g)+N(g) from enthalpies of formation (see Appendix C). Given that the CH bond enthalpy is 411 kJ/mol, obtain a value for the CN bond enthalpy. Compare your result with the value given in Table 9.5.arrow_forward
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