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Final Exam Solution

# 5 points for calculating free energy and 5 points for

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Unformatted text preview: nd entropy) to estimate ΔG(1000 K). ΔG° = ΔH° -­‐ T·∙ΔS° = -­‐484 kJ/mol – (1000K*-­‐0.089kJ/mol·∙K) = -­‐395 kJ/mol -­‐395/-­‐484 = 82% (10 points) *If you used incorrect values from previous sub-­‐questions, but had the correct setup, you were given full credit. 5 points for calculating free energy and 5 points for efficiency. Multiplied 2 to enthalpy when calculating effeciency -­‐> -­‐3 points Side 8 of 9 g) 2014 Ch 1b Final Exam SOLUTIONS We could also burn our hydrogen in an internal combustion engine. Calculate the efficiency for an engine running at 1000 K and surroundings at 298 K. Efficiency = [Th – Tl]/Th = [1000K – 298K]/1000K = 70% (5 points) *-2 points if you incorrectly converted °C to K. -­‐3 points if you tried to use free energy/enthalpy to calculate this. h) In reality the air in the engine compartment (surroundings) is probably closer to 125°C, calculate the modified efficiency under these conditions (which are still quite optimistic for internal combustion processes). Efficiency = [Th – Tl]/Th = [1000K – 398K]/1000K = 60% (10 points) *-2 points if you incorrectly converted °C to K. -5 points if you used Tl=298K,...
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