Ch. 10 & 14.2-14.3  thermodynamics test                   95 points                                                          honors chem

Show your work in an organized manner, including equation / formula, proper conversion factor(s), equation or formula, and units in your work / answer and the proper number of significant figures in your answer.

1. Given:

dH 1 

dH 2 

 dH 3

find  [10 points; weekly quiz question]

                        1_net chem eqn                   ΔH  =  ?

2. What is ΔS in the below situations (i.e. ΔS > 0; ΔS < 0; ΔS ≌ 0; ambiguous); justify / rationalize your response.  [15 points; last year’s test question]

a. Mix aqueous solutions of silver nitrate and sodium chloride

b.  Dissolve magnesium chloride in water

c.  Melting of ice

3. What is the “final” temperature of water after dissolving 2.0 grams of solid sodium hydroxide in 75 mL of water at an initial temperature of 21 ºC ?  [20 points;  weekly quiz problem]

4. Calculate the number of grams of water, where the addition of 50.0 g of copper at 100. °C would change the temperature of water by 5.0 °C; assume that the initial temperature of the water is 20.0 °C; specific heat of copper is 0.38 J / (g K).   [15 points; prelab problem]

5. Based on thermodynamics, what is the boiling point of water ?  hints:  ΔS = 123 J / K  and H2O(l)  à  H2O(g) is a chemical equation that describes it.   [10 points]

6. 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;  2 year ago test question]