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Chemical Principles
- The enthalpy change when 1 mol methane (CH4) is burned is 890 kJ. It takes 44.0 kJ to vaporize 1 mol water. What mass of methane must be burned to provide the heat needed to vaporize 1.00 g water?arrow_forwardThe standard molar enthalpy of formation of diborane, B2H6(g), cannot be determined directly because the compound cannot be prepared by the reaction of boron and hydrogen. It can be calculated from other enthalpy changes, however. The following enthalpy changes can be measured. 4 B(s) + 3 O2(g) 2 B2O3(s) rH = 2543.8 kJ/mol-rxn H2(g) + O2(g) H2O(g) rH = 241.8 kl/mol-rxn B2H6(g) + 3 O2(g) B2O3(s) + 3 H2O(g) rH = 2032.9 kJ/mol-rxn (a) Show how these equations can be added together to give the equation for the formation of B2H6(g) from B(s) and H2(g) in their standard states. Assign enthalpy changes to each reaction. (b) Calculate fH for B2H6(g). (c) Draw an energy level diagram that shows how the various enthalpies in this problem are related. (d) Is the formation of B2H6(g) from its elements exo- or endothermic?arrow_forwardA compound is 82.7% carbon and 17.3% hydrogen, and has a molar mass of approximately 60 g/mol. When 1.000 g of this compound burns in excess oxygen, the enthalpy change is 49.53 kJ. (a) What is the empirical formula of this compound? (b) What is the molecular formula of this compound? (c) What is the standard enthalpy of formation of this compound? (d) Two compounds that have this molecular formula appear in Appendix G. Which one was used in this exercise?arrow_forward
- A 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_forwardIsooctane (2,2,4-trimethylpentane), one of the many hydro carbons that make up gasoline, burns in air to give water and carbon dioxide. 2C8H18(l)+25O2(g)16CO2(g)+18H2O(l)rH=10,922kJ/mol Calculate the enthalpy change if you burn 1.00 L isooctane (density = 0.69 g/mL).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_forward
- 9.65 When 0.0157 g of a compound with a heat of combustion of —37.6 kJ/mol is burned in a calorimeter, 18.5 j of heat is released. What is the molar mass of the compound?arrow_forwardHow much heat is produced by combustion of 125 g of methanol under standard state conditions?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_forward
- One step in the manufacturing of sulfuric acid is the conversion of SO2(g) to SO3(g). The thermochemical equation for this process is SO2(g)+12O2(g)SO3(g)H=98.9kJ The second step combines the SO3 with H2O to make H2SO4. (a) Calculate the enthalpy change that accompanies the reaction to make 1.00 kg SO3(g). (b) Is heat absorbed or released in this process?arrow_forwardUsing the data in Appendix G, calculate the standard enthalpy change for each of the following reactions: (a) Si(s)+2F2(g)SiF4(g) (b) 2C(s)+2H2(g)+O2(g)CH3CO2H(l) (c) CH4(g)+N2(g)HCN(g)+NH3(g) ; (d) CS2(g)+3Cl2(g)CCl4(g)+S2Cl2(g)arrow_forwardGiven: 2Cu2O(s) + O2(g) 4CuO(s)H = 288 kJ Cu2O(s) CuO(s) + CuO(s)H = 11kJ Calculate the standard enthalpy of formation (Ht) for CuO(s).arrow_forward
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