### probability vs probability density

Posted:

**Mon Oct 14, 2019 7:56 pm**Could someone explain the difference between probability vs probability density? Thanks!

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=117&t=47552

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Posted: **Mon Oct 14, 2019 7:56 pm**

Could someone explain the difference between probability vs probability density? Thanks!

Posted: **Mon Oct 14, 2019 9:04 pm**

Probability density is a "density" function. While probability is a specific value. The probability density function for a given value of X represents the density of probability.

Posted: **Mon Oct 14, 2019 9:06 pm**

The probability density, symbolized by psi squared, is the probability that something will be found in a space divided by region volume. For example, if psi squared is 0, then there is a probability of 0 that the electron will be found in that space in that region's volume. Probability has no unit but probability density has units of volume^-1.

Posted: **Sun Nov 03, 2019 3:47 pm**

Karina Kong 1L wrote:Could someone explain the difference between probability vs probability density? Thanks!

Hi,

How I see it is probability density telling whether or not it is likely to be in a specific region of a volume, and probability as how much likely. For example, at a point, the probability density could be 0.3pm^-3 (not as likely, as it is measured from a scale from 0 (not there) to 1 (certainly there). To find probability, you would multiply by the volume of the area (0.3 pm^-3) x (2pm^3) = 0.6 , 3 out of 5 chances of being there.

- similar example found in the textbook