Excess Enthelpy for Water-Ethanol Solution

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SUMMARY

The discussion centers on the discrepancy between experimental and calculated temperature increases when mixing equal volumes of pure water and 95% ethanol. The experiment revealed a final temperature of 28.5°C after mixing 50 mL of each component, while calculations based on a mole fraction of ethanol at 0.2 and an excess enthalpy of -717 J/mol suggested only a 1.7°C increase. The key factors influencing this difference include the heat capacities of the components and the mixture, which were not specified in the calculations. Understanding these heat capacities is crucial for accurate thermal predictions in such solutions.

PREREQUISITES
  • Knowledge of thermodynamics, specifically enthalpy and heat capacity concepts.
  • Familiarity with mole fraction calculations in solutions.
  • Understanding of the properties of water and ethanol mixtures.
  • Basic laboratory techniques for measuring temperature changes in chemical solutions.
NEXT STEPS
  • Research the heat capacities of water and ethanol at various concentrations.
  • Explore the concept of excess enthalpy in binary mixtures.
  • Learn about the methods for calculating temperature changes in mixing solutions.
  • Investigate the impact of impurities on the thermal properties of ethanol solutions.
USEFUL FOR

Chemists, chemical engineers, and laboratory technicians involved in thermodynamic studies and solution chemistry will benefit from this discussion.

miz_cheme
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I am trying to determine the final temperature of a solution after I mix equal volumes of pure water and 95% by volume Ethanol (5% by volume water). Doing this experiment in the lab, I found that mixing 50 mL of water and 50 mL of 95% Ethanol gave a final temperature of 28.5 C after mixing (both the water and ethanol were at the same temperature of 22 C before mixing). Thus, mixing 50 mL of each when both were initially at 22 C gave in increase of 6.5 C.

With the mole fraction of Ethanol being about 0.2, this gives a corresponding excess enthalpy of -717 J/mol and with the total moles of Ethanol at 0.77, the added enthalpy after mixing is -553. This leads to a calculated temperature increase of only 1.7 C. What am I missing here? Why did the lab results show a temperature of 28.5 yet my math (which I am nearly 100% of correctness) only gives 1.7 C increase?
 
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What heat capacities are you using for components and for the mixture?
 

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