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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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 Spring '13
 heath,rees
 Organic chemistry, pH

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