<p>You can convert mm Hg to kPa with the conversion factor $0.133322368\ \mathrm{kPa\ mmHg^{-1}}$. </p>

<p>Saturation vapor pressure as a function of temperature is </p>

<p>$$ e_s(T) = e_{s0}\exp\left[\left(\dfrac{L_v(T)}{R_v}\right)\left(\dfrac{1}{T_0} -\dfrac{1}{T} \right)\right], $$</p>

<p>where $L_v(T)$ is the specific enthalpy of vaporization, $R_v$ is the specific gas constant for water vapor, $T_0$ is reference temperature (273.15 K) and $e_{s0}$ is the saturation vapor pressure at $T_0$ (611 Pa).</p>

<p>You can find the slope of this curve by taking the derivative $\dfrac{d e_s}{dT}$.</p>

<p>Note that the units of $e_s$ and $T$ are Pa and K respectively in the equation above.</p>

CC BY-SA 3.0
2014-09-22T20:39:48.183Z
he could also do it through wolfram alpha if its only a few conversions =)
Neo
CC BY-SA 3.0
2014-09-23T05:05:16.997Z
Well, Thank you for replying. I know the relation between kPa and mmHg. But I need to express the slope in mmHg/degree celsius instead of kPa/degree celsius. I need an equation for finding that.
user903
CC BY-SA 3.0
2014-09-22T19:38:04.837Z
2014-09-23T03:17:06.390Z
2014-09-23T03:17:06.390Z
casey
<p>finally i could find out that both units are not compatible to convert. Little bit speculated about the fact.<br>
The equation for finding the slope in mmHg/&deg;C =                             4098*(4.584*exp(17.27*T/237.3+T))/(T+237.3)^2. </p>

CC BY-SA 3.0
2014-09-23T11:47:33.423Z
2016-07-05T02:41:58.337Z
2016-07-05T02:41:58.337Z
user903
<p>How is mm of Hg per degree Celsius converted to kPa per degree Celsius? I also need  the equation for computing the value of A (slope) in mm of Hg per degree Celsius.</p>

CC BY-SA 3.0
2014-09-22T17:51:45.813Z
Is this a homework question?
Neo
CC BY-SA 3.0
2014-09-23T05:01:57.323Z
This is not a homework question.
user903
<hydrology>
Slope of Saturation vapor pressure versus temperature-A parameter in Penman's equation
user903
# Slope of Saturation vapor pressure versus temperature-A parameter in Penman's equation

(Asked by: username_0 on 2014-09-22)

How is mm of Hg per degree Celsius converted to kPa per degree Celsius? I also need the equation for computing the value of A (slope) in mm of Hg per degree Celsius.

**Tags:** hydrology

> **Comments:**
> **username_1**: Is this a homework question?  
> **username_0**: This is not a homework question.  

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## 2 answers

### Answer by username_2 on 2014-09-22. Score: 9

You can convert mm Hg to kPa with the conversion factor $0.133322368\ \mathrm{kPa\ mmHg^{-1}}$.

Saturation vapor pressure as a function of temperature is

$$ e\_s(T) = e\_{s0}\exp\left[\left(\dfrac{L\_v(T)}{R\_v}\right)\left(\dfrac{1}{T\_0} -\dfrac{1}{T} \right)\right], $$

where $L\_v(T)$ is the specific enthalpy of vaporization, $R\_v$ is the specific gas constant for water vapor, $T\_0$ is reference temperature (273.15 K) and $e\_{s0}$ is the saturation vapor pressure at $T\_0$ (611 Pa).

You can find the slope of this curve by taking the derivative $\dfrac{d e\_s}{dT}$.

Note that the units of $e\_s$ and $T$ are Pa and K respectively in the equation above.

> **Comments:**
> **username_1**: he could also do it through wolfram alpha if its only a few conversions =)  
> **username_0**: Well, Thank you for replying. I know the relation between kPa and mmHg. But I need to express the slope in mmHg/degree celsius instead of kPa/degree celsius. I need an equation for finding that.  

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### Answer by username_0 on 2014-09-23. Score: 1

finally i could find out that both units are not compatible to convert. Little bit speculated about the fact.  
The equation for finding the slope in mmHg/°C = 4098\*(4.584\*exp(17.27\*T/237.3+T))/(T+237.3)^2.


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