PLEASE ANSWER ALL THE QUESTION BELOW! This graphs are from Heat of Mixing lab. E
ID: 899565 • Letter: P
Question
PLEASE ANSWER ALL THE QUESTION BELOW!
This graphs are from Heat of Mixing lab. Ethanol and water was mixed. The x-axis of the graphs is the mole fraction of ethanol.
The questions are discussion graphs.
1. Please tell the propose reason for shape of the following graph, which is excess enthalpy plot, including literature data for comparison.
3. compare shape/trend of HE to Cp; discuss why the relationship is what it is.
4. Please make discussion of significance of data.
Excess enthalpy plot, including literature data for comparison (error bars on experimental data) 200 0 200 -400 -600 -800 1000 -1200 0.2 0.4 0.8 ·Lit Exp X EtOHExplanation / Answer
ANSWER:
(1) H vs XEtOH
(Excess enthalpy) HE = XEtOH (Hr - Hi)
Hr = Molr enthlpy in real solution
Hi = molar nthalpy in ideal solution.
All the H values are negative ((negative sign implies heat is released). It implies that the forece of attraction between the molecules of ethanol and water is greater than water-water and ethanol-ethanol attractive forces. Further H varies with the mole fraction of ethanol XEtOH, this variation gives it acharacteritic shape. Attractive force increase (H becomes more negative) as mole fraction of ethanol increases upto a certain value of XEtOH. after that the attractive force begins to decrease as XEtOH increases. Hlit values ar greater than Hexp which is indicative of less attractive force between water and ethanol in the experiment than theoritical attractive force.
(2) The plot of Cp vs XEtOH deviates from the linearity because of the interactions between water and ethanol molecules. Cp vs XEtOH has three phases. Cp increases initialy then decreases and then again increases. Explaination: initially attractive force between water and ethanol molecules increase as explained above (from graph1). Hence more energy is needed to break these forces and increase the temprature(Cp = energy needed to raise temp. of a given mass at constant pressure). After a certain values of XEtOH attractive forces begin to decrease, hence less energy is needed to to increase the temprature (= less Cp). That is why Cp decreases in second phase.
Both Q3 and Q4 are discussed in Q1 and Q2
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