The barometric pressure on a winter day in Minnesota was found to be 747 mm Hg.

Question

The barometric pressure on a winter day in Minnesota was found to be 747 mm Hg. What would the pressure be in cm H_2O? How many meters of water would it take to exert that pressure? In this experiment a student found that when she increased the temperature of a 550 mL sample of air from 22.3 degree C to 29.7 degree C, the pressure of the air went from 1009 cm H_2O up to 1033 cm H_2O. Since the air expands linearly with temperature, the equation relating P to t is of the form: P = mt + b where m is the slope of the line and b is a constant. What is the slope of the line? Find the change in P divided by the change in t.) m = _____ Find the value of b. (Substitute known values of P and t into Equation 9 and solve for h.) b =_____ Express Equation 9 in terms of the values of m and b. P = _____ At what temperature t will P become zero? The temperature in part d is the absolute zero of temperature. Lord Kelvin suggested that we set up a scale on which that temperature is 0 K. On the scale, T = t + A. Show that, on Kelvin scale, your equation reduces to P = mT.

Explanation / Answer

Q1.

note tat

1 mm Hg = 1.35951 cm H2O

so

747 mm HG --> 747 *1.35951 = 1015.55397 cm H2O

b)

this pressure will require 1015.55397/1000 = 1.015 meters

Q2.

slope of line:

P --> y

t --> x

change in P = (1033-1009)/(29.7-22.3) = 3.2432

b)

b -->

choose any point

1033 = 3.2432 * 29.7 + b

b = 1033 - 3.2432 * 29.7

b = 936.67

c)

P = 3.2432 * T + 936.67

d)

P = 0 when T = ?

0 = 3.2432 * T + 936.67

T = 936.67/-3.2432 = -288.81 °C ,i.e. not possible

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