Question Writing Session - Thermochemistry

Group 1 (Stephanie, Paul, Frances)

The reaction of aluminum powder and iron (III) oxide produces 847.6 kJ/mol of energy.  

(a) Write the complete and balanced equation including the heat term.

(b)  5.0 g of aluminum is reacted with excess iron (III) oxide. How much heat is produced?

(c) If the DHf for iron (III) oxide is -822.2, calculate the DHf for aluminum oxide.

(d) Given the following  data, calculate the DSrxn.

(e)  Is the reaction spontaneous? Give proof.

Group 2  (Beth, Debbie, Marla, Melanie)

When 50.0 mL of 2.0 M NaOH reacts with 50.0 mL of 2.0 M HCl in a calorimeter under constant pressure, the following data were collected:

NaOH initial temperature: 27.6 C

HCl initial temperature: 28.1 C

Final temperature when NaOH was combined with HCl: 61.0 C

(a)  Write the balanced equation for the reaction.

(b)  Calculate the heat of the reaction.

(c)  Calculate the standard heat of formation for water.

(d)  How would the heat of reaction change if a flimsy paper cup with no cover were used instead of an insulated, covered calorimeter?  Explain.

(e)  Which direct measurements would change if the experimenter failed to dry the calorimeter before the reaction? How would that affect the heat of reaction?

Group 3 (Adrian)

(a) The standard enthalpy of formation of water = -285.5 kJmol-1. Write an equation to illustrate the standard enthalpy of formation of H2O(l) from its elements.

(b) Using your answer to (a), calculate the enthalpy change, in kJmol-1, for the combustion of hydrogen gas.

(c) The following data is given;

C + O2 ⇒ CO2                         DH = -393.5 kJmol-1

C2H4 + 3O2 ⇒ 2CO2 + 2H2O        DH = -1411.1 kJmol-1

Use them to calculate the standard enthalpy of formation of C2H4(g).

(d) Is your answer to part (c), exothermic or endothermic? Explain your answer.

(e) Ethene C2H4, and ethane C2H6, both have carbon atoms bonded to one another. Which compound is expected to have the stronger carbon to carbon bonds? Explain your answer.

Group 4 – Paul, Rosemarie, Michele. L

Analyze the following dataAT 298k

                                delta Hof kJ/mol                delta Gof kJ/mol        So J/molK

H2O(l)                                        -285.8                                -237.2                69.9

H2O(g)                                        -241.8                                 -228.6                ?

For  the change H2O(l) -->  H2O(g)        

(a)Find delta Ho at 298K

(b)Fnd delta Go at 298K

(c)Find delta So at 298K

(d)Find So, the standard molar entropy of H2O(g), at 298K

(e)Assuming that delta H and delta S are relatively constant, find the normal boiling point of water .

Group 5 – Vaughn, Gary, Erica

For the gaseous equilibrium :   N2 + 3H2 <--> 2NH3, answer the following question

(a)  Is delta S positive or negative for the forward process.  Justify.

(b)  What change, if any would occur to delta G if temperature was decreased?  Explain your reasoning in terms of thermodynamic principles.

(c)  If you add Ne at constant volume and pressure, what happens to the reaction and the partial pressure of H2?  Explain.

(d)  Predict the sign of delta G at low temperatures.  Justify.

(e)  If the reaction is analyzed in the reverse (decomposition of ammonia) predict the sign of delta G, delta S and delta H.  

Group 6 – Ruth, Constance, Sean

Consider the reaction represented below.

O3(g) + NO(g) --> O2(g) + NO2(g)

(a)  Referring to the data in the table below, calculate the standard enthalpy change, ΔHo, for the reaction at 25 oC.  Be sure to show your work.

(b)  Make a qualitative prediction about the magnitude of the standard entropy change, ΔSo, for the reaction at 25 oC. Justify your answer.

(c)  On the basis of your answers to parts a) and b), predict the sign of the standard free-energy change, ΔGo, for the reaction at 25 oC.  Explain your reasoning.

Group 7 – Brian, Kelli, Laurie,

                                        ΔHf°          Absolute entropy  S°                                             

               Compound             (kJ/mole)               (J/mole K)                   

                  H2O(l)                 -285.8                 69.9                         

                  CO2(g)                 -393.5                        213.6

                   O2(g)                                                         205.0

            C3H8                ?                               269.8

When 2.000 gram of propane gas, C3H8, is burned at 25°C and 1.00 atmosphere, H2O(l) and CO2(g) are formed with the release of 99.88 kilojoules.

(a)   Write a balanced equation for the combustion reaction.

(b)   Calculate the molar enthalpy of combustion,  ΔH°comb, of propane in kJ/mol.

(c)   Calculate the standard molar enthalpy of formation, ΔHf° , of propane gas.

(d)   Calculate the entropy change, ΔS°comb (J/K).

(e)   Calculate the ΔG° for the reaction described above .

(f)   Calculate the Keq for this reaction

Group 8 – Steve, Michele R., Donna

(a)

(b)

(c)

(d)

(e)