1. Explain with data why the temperature decreases with time for all three solve
ID: 227909 • Letter: 1
Question
1. Explain with data why the temperature decreases with time for all three solvents? What was your expectation and does it agree?
2. Is this process exothermic or endothermic and why? Is DH of this process positive or negative and why? Use data from lab in your arguments.
Results Heat of Vaporizati SolventInitial FinalTemp. Rate Rate H-bond xothermic Temp | Temp | Change (/s) | Ranking | strength or ranking Endothermic Endothermic Water23.7 °C 20.4 °C3.3 °C02753 C/s Ethanol 24.5 °C 14.1 °C 10.4 °C495 2Endothermic 3Endothermic C/s Acetone 23.6 °C 20.1 °C3.5 °C.36Explanation / Answer
1) Any solvent having boiling point below 100 oC undergoes evaporation when kept for sometime undisturbed. This is because it uses the energy from the surrounding to break free from the intermolecular attraction in the liquid phase. Since, it uses the surrounding heat, so it has a cooling effect. So, temperature decreases with time for all the three solvents.
More the interation between the liquid molecule, lesser is the evaporation and hence the cooling effect. Since, the hydrogen bond strength in the solvent follows the order water>ethanol>acetone, thus it is expected that the rate of temperature change should follow the reverse order.
2) dH of the process is endothermic and so it is positive. The process is endothermic as it utilizes energy from the surrounding to break from the intermolecular attractions.
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