Thermochemistry

 

The following problems are taken from T. L. Brown, H. E. Lemay, B. E. Bursten, & J. R. Burdge, Chemistry: The Central Science, Ninth Edition, Chapter 5. To see the solution to a problem or to return from the solution, click on the number of the problem.

 

34)  Consider the following reaction:        

       CH3OH(g) CO(g) + 2H2(g)          ∆H = +90.7 kJ

       (a) Is heat absorbed or evolved in the course of this reaction?

       (b) Calculate the amount of heat transferred when 1.60 kg of CH3OH(g) are decomposed by this reaction at constant pressure.

       (c) For a given sample of CH3OH, the enthalpy change of reaction is 64.7 kJ. How many grams of hydrogen gas are produced?

       (d) What is the value of ∆H for the reverse of the previous reaction? How many kilojoules of heat are released when 32.0 g of CO(g) reacts completely with H2(g) to form CH3OH(g) at constant pressure?

       

50) When a 3.88 g-sample of solid ammonium nitrate dissolves in 60.0 g of water in a coffee-cup calorimeter, the temperature drops from 23.0°C to 18.4°C. Calculate ∆H (in kJ/mol NH4NO3) for the solution process

        NH4NO3(s)   NH4+(aq) + NO3-(aq)          

      Assume the specific heat of the solution is the same as that of pure water.

            

60) From the heats of reaction

      2H2(g) + O2(g) 2H2O(g)           ∆H = -483.6 kJ          

                    3O2(g) 2O3(g)              ∆H = +284.6 kJ

      calculate the heat of reaction for

      3H2(g) + O3(g) 3H2O(g)

 


72) Calculate the value of ∆H° for each of the following reactions:      

      (a) N2O4(g) + 4H2(g) N2(g) + 4H2O(g)       

      (b) 2KOH(s) + CO2(g) K2CO3(s) + H2O(g)

      (c) SO2(g) + 2H2S(g) (3/8)S8(s) + 2H2O(g)

      (d) Fe2O3(s) + 6HCl(g) 2FeCl3(s) + 3H2O(g)

 

84) The heat of combustion of ethanol, C2H5OH(l), is -1367 kJ/mol. A batch of sauvignon blanc wine contains 10.6% ethanol by mass. Assuming the density of the wine to be 1.0 g/mL, what caloric content does the alcohol (ethanol) in a 6-oz glass of wine (177 mL) have?

             

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