When do we use PV=nRT for Chem Equilibrium?

[Jon Phan 1B]

When do we use PV=nRT for Chemical Equilibrium questions. What is an example of a question where we would need to use the ideal gas law?

[Ayaan_Ekram_2J]

Hello!

I believe in this course the most common example of when we may need to use PV=nRT is if we are asked to find an equilibrium constant, but instead of being given just concentrations to find K_C or just partial pressures to find K_P, we are given a combination of partial pressures and concentrations. As a result, one would have to use PV=nRT to convert all values to either concentrations or partial pressures. I hope this helps!

[Wesley Zhou 1F]

PV=nRT shows us the relationship between a gas' pressure and its concentration/temperature within a system.

I think a good example of a question in which we need to use the ideal gas law is when dealing with answers that require you to convert concentration into pressure. Like, when you do an ICE box and convert the solved equilibrium values into pressure before plugging it into the K expression.

[MaiVyDang2I]

I don't think we have to use the PV=nRT equation for calculating K unless they ask specifically for Kp or to calculate Kp when given concentration.

[Matthew Nguyen 2F]

I think PV=nRT is used in order to find the pressure of gases in order to find the Kp of a certain reaction. Rearrange the equation and you get P=(n/V)RT.

[Quynhanh Nguyen 1C]

Hi! We use PV = nRT when we're not given substances with uniform units. We could either rearrange the equation to n/V = P/RT in order to get molarity or P = (nRT)/V in order to get partial pressure. Hope that helps!

[Aryan Gajjar 3D]

When you have three of the four parameters of a gas: pressure, volume, number of moles, and temperature, use this equation.

[Irene Kim 3E]

We use this equation most often when multiple variables are involved (i.e., pressure, volume, molar concentration, and/or temperature). For example, when we derive an answer in terms of pressure but we want to convert it to molar concentration, we can rewrite the equation as P = (n/V)RT where P is pressure and concentration is n/V (number of moles per unit of volume).

[Shreya Arcot 3K]

We can use this equation to find the concentration of gases:

PV = nRT
*divide both sides by V (volume)
P = (nRT)/V
*the n/V on the right side of the equation is mol/L (concentration). when we isolate the n/V, we get:
(n/V) = (mol/L) = P/(RT)

[Xzandalyn Kallstrom 2C]

You don’t really need to use PV=nRT for equilibrium problems, you use PV=nRT to find any missing values in the equation. You can only use the ideal gas law equation if you are only missing one value, for example if you are given the volume, mols, and temperature, you can find the pressure by rearranging the equation to be P=nRT/V and solving for P. You only need to use PV=nRT when being asked to find the equilibrium constant in some problems.

[Angela Harrington 2L]

In chemical equilibrium questions, you will most often use PV=nRT to convert between Kp (for partial pressure) and Kc (molar concentration) equilibrium constants.