Vapor Pressure and Heat of Vaporization Worksheet Sofia Bautista Andrew Martinez PDF

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Sofia Bautista, Andrew Martinez 2/7/18 Chem lab

Vapor Pressure and Heat of Vaporization Worksheet Name: Sofia Bautista, Andrew Martinez

Date 2/7/18

Provide a brief statement of the purpose of this activity. Be sure to include the meaning of enthalpy of vaporization and why vapor pressure is temperature dependent. Additionally show the Clausius-Clapeyron equation and describe how vapor pressure and temperature data can be manipulated to find the enthalpy of vaporization. The purpose of this lab is to measure the pressure within a sealed flask containing ethanol over a range of temperatures to determine the relationship between pressure and temperature, and calculate the heat of vaporization of the ethanol liquid. The enthalpy of vaporization is the energy required to cause a solution to undergo a physical state change from a liquid into a gas. Vapor pressure is dependent of temperature because of Gay-Lussac’s Law, which states that temperature and pressure increase/decrease in a directly proportional relationship. The Clausius-Clapeyron equation relates the following variables: ln(P2  )= - (Hvap)   x ( 1  -  1 ) P1 R T2 T1 , which can be manipulated to determine the enthalpy of vaporization by arranging the variables as follows: Hvap= R ln (P2/P1) 1/T1 - 1/T2

Data Table Include a data table that shows Temperature, Ptotal, Pair, Pvap, 1/T and lnPvap. It should include a descriptive caption. Vapor pressure v.s Heat of vaporization Data Pressure total

Temperature ( ° C)

P_air

Pvap 1/T (ethanol)

InPvap

Temperature(K ) ( ° C+273)

93.3

0.2

91.7

1.6

0.0036 0.47000 603221 36292 08

273.2

94.2

3.7

92.942 1.257179 0.0036 0.22887 82051 487 140224 07095 07

276.7

95.1

6.4

93.849 1.250256 0.0035 0.22334 74359 41 790980 86585 67

279.4

Sofia Bautista, Andrew Martinez 2/7/18 Chem lab

96.3

9.4

94.857 1.442564 0.0035 0.36642 4359 103 410764 21569 87

282.4

97.7

12.4

95.865 1.834871 0.0035 0.60697 12821 795 038542 46125 4

285.4

99.4

15

96.738 2.661538 0.0034 0.97890 46154 462 722222 43246 22

288

100.4

18.1

97.779 2.620256 0.0034 0.96327 74359 41 352456 21795 2

291.1

102.5

22

99.089 3.410256 0.0033 1.22678 74359 41 898305 7482 08

295

103.8

24.5

99.929 3.870512 0.0033 1.35338 48718 821 613445 701 38

297.5

106.3

27.1

100.80 5.497179 0.0033 1.70423 28205 487 322225 514 92

300.1

108.4

30.3

101.87 6.522307 0.0032 1.87522 76923 692 970656 8254 12

303.3

111

33.3

102.88 8.114615 0.0032 2.09366 53846 385 647730 6804 98

306.3

113.7

36

103.79 9.907692 0.0032 2.29331 23077 308 362459 1456 55

309

118.1

41.2

105.53 12.56102 0.0031 2.53059 89744 564 826861 8817 87

314.2

Sofia Bautista, Andrew Martinez 2/7/18 Chem lab

Graph Include a plot the natural log of Pvap vs. the reciprocal of absolute temperature. In the caption, include the equation of the line of best fit.

The equation that lines best fit is y= - 5736.8x + 18.456. Vapor Pressure is located on the y-axis and heat of vaporization on the x-axis(would not let me edit captions on my y and x axis).

Analysis Describe how the Pair was calculated for the differing temperatures, show a sample. Pressure of ethanol vaporization was given as 1.60kPa. The equation used was Ptotal= P air+ P vap. We rearranged it to be Pair = initial pair(temp) / initial temp. An example of calculating it at 6.4 celsius: Pair=90.1(279.4)/273.2 =  93.8kPa

Report your value for ΔHvap of ethanol. Show the calculation used to arrive at the reported value. y=- 5736.8x + 18.456.

Sofia Bautista, Andrew Martinez 2/7/18 Chem lab

5736.8molK(8.134J/molK)= 46663.13 J 46663.13J(1kJ)/1000J=46.66kJ

The accepted value of the ΔHvap of ethanol is 42.32 kJ/mol. Report the percent error in your calculated value of ΔHvap for ethanol. 42.32 kJ/mol-4 6.66kJ= -4.34/42.32=-0.1025(100%)=-10.25%

Is your value for the ΔHvap greater than or less than the accepted value? Think of some valid sources of error to account for your difference and explain how they would contribute to the direction of your error. The value for the ΔHvap is less than the accepted value. A source of error could have been using to much or to little ice, this could affect the rise of temperature. Another source of error is not properly having the flask of ethanol covered in the ice water. This could affect the pressure change since the ethanol is not reacting fully. A last source of error is having improper and poor equipments, this affects both temperature and pressure because on improper measurements. These sources of errors could be corrected by using the correct amount of ice, properly placing the ethanol flask in the ice water, and using new or advanced equipment.

Vapor Pressure and Heat of Vaporization Worksheet There is not a formal lab report for this lab. Complete the above pages and submit them to your TA in the dropbox...