i need the formula how to calculet wather boil if you are 7000 feet abave sea level ?

Answer 1

Water starts to boil, when its vapor pressure reaches the atmospheric pressure.

The latter one is given by the barometric formula:
p = p₀·exp{-g·M / (R·T₀) · h}
where
g earth gravitation constant → g₀= 9.80665 m/s²
R universal gas constant → R=8.31432 J / (mol·K)
M molar mass of air → M = 28.9644·10⁻³ kg/mol
h height above sea level
T₀ temperature at sea level T₀ = 288.15K
p₀ atmospheric pressure at sea level p₀ = 1,01325bar
(the last two values i take from International Standard Atmosphere data)

The vapor pressure can be described by the Antoine equation, which has the same form as the Clausius-Clapeyron equation :
ln pw = A − (B / (T + C))
<=>
pw = exp{A − (B / (T + C))}
where A,B and C are parameters of the substance
From NIST chemistry webbook i obtained the following values for water (pw in bars, T from 344 - 373 K). :
A = 11.70528
B = 3829.487
C = -45.622
(i multiplied the values for A and B by ln10 to shift from common logarithm to natural logarithm)


Join both equations together and solve for T:
p₀·exp{-g·M / (R·T₀) · h} = exp{A − B / (T + C)}
<=>
ln{p₀} - g·M / (R·T₀) · h = A − B / (T + C)
<=>
T = B / (A - ln{p₀} - g·M / (R·T₀) · h) - C

For h = 7000ft = 2133.6m i get a boiling temperature of
T = 366.2 K = 93.1°C

Answer 2

check the ref provided below
The Clapeyron's Equation which shows that the boiling temperature (in degrees Fahrenheit) is related to pressure as follows:

Temperature = b / log(Pressure/a) - 459.7

where a and b are parameters whose values are to be determined by the analysis. (http://www.nlreg.com/boil.htm)