# How to calculate change in pressure from LN2 phase change

• AndyPivot
In summary, the increase in pressure caused by liquid nitrogen changing from liquid to vapor within a closed, constant volume at atmospheric pressure can be calculated by finding the vapor pressure at a given temperature and the volume of gas in equilibrium with the liquid. The temperature and pressure will increase as the liquid evaporates, until reaching the critical temperature.
AndyPivot
I am trying to calculate the increase in pressure caused by liquid nitrogen when it changes from liquid to vapor within a closed, constant volume at atmospheric pressure. How can this be done? Do I need to include the heat of vaporization?

So, the vapor pressure is an accurate representation of the pressure exerted by the LN2 gas on the walls of any closed container?

Last edited:
AndyPivot said:
increase in pressure...at atmospheric pressure. How can this be done?
Zero is identically "zρ." Now, what is your question? Did you want vapor pressure as a function of temperature?

Let's say you start with a mol of LN2 at one atmosphere at its boiling temperature, and you fix a cap on it (constant volume). You can look up the volume it displaces and the temperature on your own...

Add heat until it's all evaporated. As it evaporates, pressure rises, and boiling temperature rises. You know you have a molar volume of vapor (starting with one mol N2), so look up the temperature/pressure of N2 gas with that molar volume in equilibrium with liquid. If you run out of table before you get to that volume, then you can probably stop at the critical temperature, and find the (supercritical) pressure that provides the correct molar volume.

## 1. What is the formula for calculating change in pressure from LN2 phase change?

The formula for calculating change in pressure from LN2 phase change is P = P0 * (T/T0)n, where P is the new pressure, P0 is the initial pressure, T is the new temperature, T0 is the initial temperature, and n is the coefficient of thermal expansion for LN2.

## 2. How do I determine the coefficient of thermal expansion for LN2?

The coefficient of thermal expansion for LN2 can be found in reference tables or by using the equation n = (1/V) * (δV/δT), where V is the volume of LN2 and δV/δT is the change in volume with respect to change in temperature.

## 3. Can I use the ideal gas law to calculate pressure change during LN2 phase change?

No, the ideal gas law is not applicable during phase change as it assumes a constant temperature and volume. The formula for change in pressure from LN2 phase change takes into account the change in temperature and volume of LN2.

## 4. What temperature and pressure values should I use in the formula for calculating change in pressure?

You should use the temperature and pressure values at the start and end of the phase change. These values can be measured using a thermometer and pressure gauge.

## 5. Is the change in pressure during LN2 phase change always the same?

No, the change in pressure during LN2 phase change can vary depending on the initial temperature and pressure, as well as the amount of LN2 being used. It is important to measure the temperature and pressure accurately in order to calculate the change in pressure correctly.

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