No Change in Volume of Liquid When moles increase

[Irene Oh 2A]

In Friday's (2/3) lecture, Dr. Lavelle talks about how a reaction converting 2 mol of liquid to 3 mol of liquid wouldn't increase the volume because the number of atoms stays the same. I'm still not understanding why the number of atoms would stay the same if moles of liquid increase. Could someone please explain this phenomenon in more detail to me?

[Brianna Gianetto 3E]

Hi! This is because the system you are looking at is closed. There is no matter going in and out of the system and therefore the amount of total atoms stays the same. When you convert 2 moles of liquid to 3 moles of liquid, you are simply rearranging the already present atoms into more molecules that have less atoms per molecule. Even though you technically have more molecules, they are smaller and take up less space, therefore occupying the same volume as before.

[Gavin_Yang_1J]

To add onto this, I think the reason you might be confused is because when we look at gases we say that more moles of gas equals greater volume of gas. The reason for this is because we assume the gases are ideal and very little of the volume of the gas is the actual gas molecules but rather the way in which the molecules are moving and colliding. Thus for gases more molecules would mean that more individual particles are moving around which would increase volume even though the amount of matter is still the same.

[Margreet Gawargious lecture 2 section 2H]

The conversion of 2 moles of liquid to 3 moles of liquid in a closed system results from the atoms' rearrangement. because the system is closed, the volume of the liquid is fixed, and the only parameter that can change is temperature. When the temperature changes the rearrangement of the molecules within the liquid can change resulting in larger or smaller molecules made up of the same atoms as the original liquid. We can assume that the temperature change resulted in smaller molecules therefore the moles of liquid increased.