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The reason there is danger in exposure to high-energy radiation (e.g., ultraviolet and X rays) is that the radiation can rupture
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MOLECULAR NATURE OF MATTER 7/E LL W/AC
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- 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_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_forwardIn 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…arrow_forward
- These UV photons can break chemical bonds in your skin to cause sunburn- a form of radiation damage. If the 330 nm radiation provides exactly the energy to break an average chemical bond in the skin, estimate the average energy of these bonds in kJ/mol.arrow_forwardA scientist studies the bond energies of different compounds containing nitrogen (N). The scientist observes that the N–N bonds in one group of compounds have a bond energy of 209 kJ/mol, while the N–N bonds in another group of compounds have a bond energy of 418 kJ/mol. In one or two sentences, postulate a reason for this difference.arrow_forwardThe enthalpy change for the reaction between two molecules of carbon oxysulfide (COS) to form one molecule of CO2 and one molecule of CS2, as shown below, is –3.2 × 10–24 kJ per molecule of COS. The bond energy for the C=S bond in CS2 has been determined to be 552 kJ/mol. What is the apparent bond energy of a carbon–sulfur bond in COS? Use the bond energies below. Bonds Bond Energy(kJ/mole) C=S 552 C=O 799 Note: A C=O bond adjacent to another double bond is not the same as a C=O bond that is not adjacent to another double bond.arrow_forward
- Activating C-H bonds is a popular research target for chemists, particularly for pharmaceuticals. Older methods used light to initiate the bond breaking. Breaking 1 mole of C-H bonds requires about 413 kJ. What would be minimum frequency of a photon needed to break a single (1) C-H bond? O 103 × 1015 Hz 5.25 × 1015 Hz O 4.98 × 1014 Hz O 8.72 × 1014 Hz хarrow_forwardMany free radicals combine to form molecules that do not contain any unpaired electrons. The driving force for the radical- radical combination reaction is the formation of a new electron-pair bond. Consider the formation of hydrogen peroxide. 2 OH(g) → H₂O₂(g) Write Lewis formulas for the reactant and product species in the chemical equation. Include nonbonding electrons. OH(g) Select Draw Rings More / ||| ||| Erase Q2 Q H₂O₂(g) Select Draw Rings More 3 S H Erase Q2 Q Question Source: McQuarrie, Rock, And Gallogly 4e - General Chemistry Publisher: University Science Barrow_forwardUse the molar bond enthalpy data in the table to estimate the value of AHin for the equation CC14(g) + 2 F₂ (g) → CF₁ (g) + 2 Cl₂ (g) 2 The bonding in the molecules is shown. ΔΗ +=++· rxn = -CI F-F F-F -C-F CI-CI CI-CI Average molar bond enthalpies (Hbond) Bond Bond O-H C=N 0-0 N-H C-O N-N 0=0 N=N C=O N=N C-C F-F C=C Cl-Cl C=C Br-Br C-H H-H C-F H-F C-Cl H-Cl C-Br H-Br C-N H-S C=N S-S kJ.mol-¹ 464 142 351 502 730 347 615 811 414 439 331 276 293 615 kJ.mol-1 890 390 159 418 945 155 243 192 435 565 431 368 364 225 kJ.mol-¹arrow_forward
- Hydrazine, N2H4, burns in oxygen as follows: N2H4 + O2 → N2 + 2H2O [The bond energies in kJ/mol are: N-H = 388; N-N 163; N≡N 944; O-H 463; O=O 496] Draw the chemical structures of the reactants and products and give the formula to calculate enthalpy change in a reaction, ΔH.arrow_forwardUse average bond energies together with the standard enthalpy of formation of C( g) (718.4 kJ/mol) to estimate the standard enthalpy of formation of gaseous benzene, C6H6( g). (Remember that average bond energies apply to the gas phase only.) Compare the value you obtain using average bond energies to the actual standard enthalpy of formation of gaseous benzene,82.9 kJ/mol. What does the difference between these two values tell you about the stability of benzene?arrow_forwardUse the Born-Haber cycle to calculate the lattice energy of KF. [The heat of sublimation of K is 91.6 kJ·mol−1 and ΔfH(KF) = −567.3 kJ·mol−1. Bond enthalpy for F2 is 158.8 kJ·mol−1. Other data may be found in the Ionization Energies Table and the Electron Affinities Table.]arrow_forward
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