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The methane molecule, CH4, has the geometry shown in Figure 2.17. Imagine a hypothetical process in which the methane molecule is "expanded, " by simultaneously extending allfour bonds C-H bonds to infinity. We then have the process:
(a) Compare this process with the reverse of the reaction thatrepresents the standard enthalpy of formation of CH4(g).
(b) Calculate the enthalpy change in each case. Which is themore endothermic process? What accounts for the difference inΔHo values? (c) Suppose that 3.45 g CH4(g) reacts with1.22 g F2(g), forming CH4(g) and HF(g) as sole products. What is the limiting reagent in this reaction? If reaction occurs at constant pressure, What amount of heat is evolved?
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Chapter 5 Solutions
Chemistry: The Central Science (13th Edition)
- What mass of acetylene, C2H2(g), must be burned to produce 3420 kJ of heat, given that its enthalpy of combustion is 1301 kJ/mol? Compare this with the answer to Exercise 5.91 and determine which substance produces more heat per gram.arrow_forwardWhen 2.50 g of methane burns in oxygen, 125 kJ of heat is produced. What is the enthalpy of combustion per mole of methane under these conditions?arrow_forward9.41 Under what conditions does the enthalpy change equal the heat of a process?arrow_forward
- Is the following reaction the appropriate one to use in determining the enthalpy of formation of methane, CH4(g)? Why or why not? C(g)+4H(g)CH4(g)arrow_forwardThe enthalpy change for the following reaction is 393.5 kJ. C(s,graphite)+O2(g)CO2(g) (a) Is energy released from or absorbed by the system in this reaction? (b) What quantities of reactants and products are assumed? (c) Predict the enthalpy change observed when 3.00 g carbon burns in an excess of oxygen.arrow_forwardWhich of the enthalpies of combustion in Table 5.2 the table are also standard enthalpies of formation?arrow_forward
- 9.73 Without looking up any numerical data or doing calculations, predict whether the enthalpy change for each of the following reactions should he positive, negative, or zero. (a) H2O(l)H2O(s) (b) N2(g)2N(g) (c) CH4(g)+2O2(g)CO2(g)+2H2O(l) (d) CO2(s)CO2(g)arrow_forwardThe first step in the preparation of lead from its ore (galena, PbS) consists of roasting the ore. PbS(s)+32O2(g)SO2(g)+PbO(s) Calculate the standard enthalpy change for this reaction, using enthalpies of formation (see Appendix C).arrow_forwardA 0.470-g sample of magnesium reacts with 200 g dilute HCl in a coffee-cup calorimeter to form MgCl2(aq) and H2(g). The temperature increases by 10.9 C as the magnesium reacts. Assume that the mixture has the same specific heat as water and a mass of 200 g. (a) Calculate the enthalpy change for the reaction. Is the process exothermic or endothermic? (b) Write the chemical equation and evaluate H.arrow_forward
- Chlorine dioxide, ClO2, is a reddish yellow gas used in bleaching paper pulp. The average speed of a ClO2 molecule at 25C is 306 m/s. What is the kinetic energy (in joules) of a ClO2 molecule moving at this speed?arrow_forwardGive the definition of the standard enthalpy of formation for a substance. Write separate reactions for the formation of NaCl, H2O , C6H12O6, and PbSO4 that have H values equal to Hf for each compound.arrow_forwardNiagara Falls has a height of 167 ft (American Falls). What is the potential energy in joules of 1.00 lb of water at the top of the falls if we take water at the bottom to have a potential energy of zero? What would be the speed of this water at the bottom of the falls if we neglect friction during the descent of the water?arrow_forward
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