9.10 The kinetic energy of molecules is often used to induce
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Chapter 9 Solutions
Chemistry for Engineering Students
- Bond 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_forwardThe bond energy for a CH bond is about 413 kJ/mol in CH4 but 380 kJ/mol in CHBr3. Although these values are relatively close in magnitude, they are different. Explain why they are different. Does the fact that the bond energy is lower in CHBr3, make any sense? Why?arrow_forwardThe molecular structure shown is of one form of glucose, C6H12O6 Glucose can be oxidized to carbon dioxide and water according to the equation C6H12O6(S) + 6 O2(g)6 CO2(g) + 6 H2O(g) (a) Using the method described in Section 6-6a for estimating enthalpy changes from bond energies, estimate rH for the oxidation of this form of glucose. Make a list of all bonds broken and all bonds formed in this process. (b) Compare your result with the experimental value of 2816 kJ/mol for combustion of glucose. Why might there be a difference between this value and the one you calculated in part (a)?arrow_forward
- Using the bond dissociation enthalpies in Table 8.8, estimate the enthalpy of combustion of gaseous methane, CH4, to give water vapor and carbon dioxide gas.arrow_forwardWrite Lewis structures for CO32, HCO3, and H2CO3. When acid is added to an aqueous solution containing carbonate or bicarbonate ions, carbon dioxide gas is formed. We generally say that carbonic acid (H2C03) is unstable. Use bond energies to estimate E for the reaction (in the gas phase) H2CO3CO2+H2O Specify a possible cause for the instability of carbonic acid.arrow_forwardDinitrogen monoxide, N2O, can decompose to nitrogen and oxygen gas: 2 N2O(g) 2 N2(g) + O2(g) Use bond dissociation enthalpies to estimate the enthalpy change for this reaction.arrow_forward
- Acetic acid has the structure CH3CO(OH), in which the OH group is bonded to a C atom. The two carbonoxygen bonds have different lengths. When an acetic acid molecule loses the H from the OH group to form the acetate ion, the two carbonoxygen bonds become equal in length. Explain.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_forwardhat is the enthalpy change for a process? Is enthalpy a state function? In what experimental apparatus are enthalpy changes measured?arrow_forward
- The reaction of quicklime, CaO, with water produces slaked lime, Ca(OH)2, which is widely used in the construction industry to make mortar and plaster. The reaction of quicklime and water is highly exothermic: CaO(s)+H2O(l)Ca(OH)2(s)H=350kJmol1 (a) What is the enthalpy of reaction per gram of quicklime that reacts?. (b) How much heat, in kilojoules, is associated with the production of 1 ton of slaked lime?arrow_forwardBest Lewis Formula and Molecular Geometry A student writes the Lewis electron-dot formula for the carbonate anion, CO32, as a Does this Lewis formula obey the octet rule? Explain. What are the formal charges on the atoms? Try describing the bonding for this formula in valence bond terms. Do you have any difficulty doing this? b Does this Lewis formula give a reasonable description of the electron structure, or is there a better one? If there is a better Lewis formula, write it down and explain why it is better. c The same student writes the following resonance description for CO2: Is there something wrong with this description? (What would you predict as the geometries of these formulas?) d Is one or the other formula a better description? Could a value for the dipole moment help you decide? e Can you write a Lewis formula that gives an even better description of CO2? Explain your answer.arrow_forwardWrite Lewis structures for CO32, HCO3, and H2CO3. When acid is added to an aqueous solution containing carbonate or bicarbonate ions, carbon dioxide gas is formed. We generally say that carbonic acid (H2CO3) is unstable. Use bond energies to estimate H for the reaction (in the gas phase) H2CO3 CO2 + H2O Specify a possible cause for the instability of carbonic acid.arrow_forward
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