Ch. 10 & 14  thermodynamics              test                 [90 points]                               honors Chem

 

For problems involving calculations, show your work in an organized manner, include any relevant equation (or formula and conversion factor(s)), put the proper units in your calculations / answer, and have the proper number of significant figures in your answer.  Clearly identify the problems done and do them in sequence and your answer must begin and end on the same page of paper; otherwise, you will lose points.  attach this sheet to the front of your exam.

 

Academic Honesty:   The answers on this test are my own and I am using only the allowed set of notes as described in the syllabus.  I have not discussed the test questions with anyone before or during the test nor have I seen the test questions prior to the exam.  If you violate any of the preceding items or do not sign, your semester grade is a F.

 

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1.  2.50 grams solid NaOH was dissolved in 50.0 mL water; the water’s initial temperature is 21.0 °C.  [20 points]

a.  write the chemical equation describing this process; include notation of its phase (i.e. g, l, s, aq)

b.  determine the change in enthalpy of the above reaction

c.  how much heat would be consumed / generated  by 2.50 g of sodium hydroxide dissolving in water ?

d.  what is the change in temperature ?

e.  what is the final temperature (before it returns to its original temperature) of the water after the addition of the sodium hydroxide ?

 

 

2.  50.0 gram piece of  metal (it’s specific heat is 0.50 J / (g-°C)) was allowed to equilibrate for awhile in a 100.0 °C boiling water bath then transferred to a calorimeter containing 75.0 mL water at 21.0 °C.  What is the final temperature of the water (i.e. its highest temperature before it returns to its original temperature) in the calorimeter ?  [10 points]

 

 

3.  Ethanol, C2H5OH, melts at – 114 °C and boils at 78 °C.  The enthalpy of fusion is 5.02 kJ / mol and its enthalpy of vaporization is 38.56 kJ / mol.  The specific heats of solid, liquid, and gas is 0.97 J / g-°C, 2.3 J /g-°C, and 1.88 J / g-°C, respectively.  How much heat to convert 50.0 g of ethanol at -150 °C to vapor phase at 78 °C ?  [25 points]

 

 

4.  Given the following data  [20 points]

 

            Fe2O3  +  3 CO  à  2 Fe  +  3 CO2                   Δ H = - 23 kJ

            3 Fe2O3  +  CO  à  2 Fe3O4  +  CO2                 Δ H = - 39 kJ

            Fe3O4  +   CO  à  3 FeO  +  CO2                     Δ H = 18 kJ

 

calculate Δ H for the reaction

            FeO  +  CO  à  Fe  +  CO2.

 

 

5.  Predict and rationalize the sign of ΔS: negative, zero, or positive – in the reaction?  [15 points]

a.  the combustion of gaseous ethane, C2H6

b.  mixing aqueous solutions of silver nitrate and sodium carbonate

c.  dissolving solid calcium chloride in water