INTRODUCTION TO GEOCHEMISTRY (GCH 3303) HOMEWORK #5 Due: March 6, 2018 The mater

Question

INTRODUCTION TO GEOCHEMISTRY (GCH 3303) HOMEWORK #5 Due: March 6, 2018 The material covered in this homework assignment relates directly to thermodynamics. Show all your work 1. Write a balanced reaction for the dissolution of magnesite (Mgco,ws) releasing COp(p when dissolved in hydrochloric acid (HCI). Assume the magnesite dissolves completely producing water, CO.w and ions in solution. 2. Calculate the change in volume for the reaction of magnesite dissolving in HCL 3. Calculate how much work is done if the above reaction proceeds at standard conditions 4. Is this reaction exothermic or endothermic? 5. Caleulate the change in internal energy for the above reaction 6. Calculate the volume of CO; released at stamdard conditions when 32g of magnesite (MgCOs co) is dissolved in HCL 7. Continuing from question 6: With temperature held constant, if the COru acts as an ideal gas and its allowed to expand reversibly against a pressure of 0.4 bar what is work done by the system? Standardcodirians-298.1 5 K (25 ) and l bar Ideal Gas Law PV nRT Conversion Factors and Constants l cal 1 bar 0.10J cm l atm 1.01325 bar 1 cm .10J bar 0°C 273.15 K 4.184J 8.3145 J mol K- Thermodynamic Data Species/ Phases MgCOs Mg2 CI CO2(w HCI H2O AHU molb') -1095.8 466.85 -167.159 393.509 167.159 -285.83 V° (em' mot) 28.018 50.0 17.3 24.7892 L mot 173 18.068

Explanation / Answer

1. The reaction between magnesite and hydrochloric acid can be written as:

MgCO3 + 2HCl -> Mg2+ + Cl2- + CO2 + H2O

2. Change in volume = Vproducts - Vreactants

= (50 + 34.6 + 24789.2 + 18.068) cm3 - (28.018 +34.6) cm3

= 24891.86 cm3

3. Work done on the system (W) = PV = (0.1)(24891.86) = 2489.1 Joules

4. Since the change in enthalpy of the reaction is negative, i.e. Hproducts - Hreactants = -50.389kJ, the reaction is exthermic.

5. Change in internal energy (U) = H - W

= (Hproducts - Hreactants) - PV

= (-50.389/1000) - (2489.186) = -2489.236 Joules

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