The data obtained in an experiment to determine the enthalpy of vaporization for

Question

The data obtained in an experiment to determine the enthalpy of vaporization for water are shown in the table on the next page. Complete the table, leaving the shaded cells blank. On the attached piece of graph paper, make a graph of ln(Pvap) as a function of 1/T, where T is the Kelvin temperature. Determine the slope of your line. Answer: _____ Determine the enthalpy of vaporization for water according to the data given. Answer: ______ Explain why a pressure cooker is able to cook food faster than boiling in an open pot. In this experiment, it is assumed that the total pressure inside the graduated cylinder (partial pressure of air plus vapor pressure of water) is the same as atmospheric pressure. However this assumption is not exactly true. Explain the source of the error. (Hint- Review step #12 of the Alloy Analysis procedure.) CALCULATION OF n air USING LOWEST TEMPERATURE: CALCULATIONS FOR FIRST TEMPERATURE / VOLUME MEASUREMENT:

Explanation / Answer

nair = 753 * 0.0013157* (4.59*10^-3)/(0.082*277)

= 0.0002

for row 1 :

T(K) = 273 + T(C)

= 273 + 75 = 348

1/T (K -1) = 1/348 = 0.00287356

Vair(mL) = V(mL) - 0.2

= 9.6 - 0.2 = 9.4

Note : 0.2 is subtracted for meniscus corrections since readings are taken observing lower meniscus

P air = nair * R*T/Vair

Note : value of R has been taken as 62.36 to get pressure in units of torr and 1000 has been multiplied to convert V from mL to L

= =0.0002*62.36*1000*348/9.4

= 461.729362

P vap = P atm - P air

= 753 - 461.729362

= 291.270638

ln (P vap) = ln (291.270638) = 5.67425286

Temp(.C) V(mL) Temp,T(K) 1/T(K-1) Vair(mL) Pair(torr) Pvap(torr) ln(Pvap) 75 9.6 348 0.00287356 9.4 461.729362 291.270638 5.67425286 70 8.52 343 0.00291545 8.32 514.170192 238.829808 5.4757512 65 7.68 338 0.00295858 7.48 563.574332 189.425668 5.2439967 60 7.11 333 0.003003 6.91 601.038495 151.961505 5.02362723 55 6.67 328 0.00304878 6.47 632.274498 120.725502 4.79351939 50 6.32 323 0.00309598 6.12 658.244444 94.7555556 4.55130048 4 4.79 277 4.59

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