Question

What are the characteristics of a substance in the gas phase?

made up of particles packed closely together, having both definite shape and definite volume
made up of particles packed relatively close together, having an indefinite shape but a definite volume
made up of particles that are far apart from each other, having both indefinite shape and indefinite volume
made up of positively charged particles and negatively charged electrons, having indefinite shape and indefinite volume

Answer 1

When we think of something in the solid, liquid and gas phases:
-A solid is something which we can pick up and hold, it has a set shape which never changes unless we break it up or deform it. In a solid, the particles (molecules/atoms) are held in fixed rigid positions with respect to one another and cannot move, only vibrate. The atoms/molecules usually have very strong interactions with one another, whether due to electrostatic attractions in lattice structures (positive and negative charges attracted to one another) or due to very stable covalent bonding structures.

-A liquid is something which we generally something which we don't associate with having a fixed shape. The molecules/atoms will conform to the shape of the container which we have them in, but will not spread out so much as to fill the entirety of the available space (i.e. they have a certain fixed volume). Whilst the molecules in a liquid have enough energy so that they can move with respect to one another (they flow or slide past one another), the attractive strength of their interactions (e.g. dipole-dipole interactions, hydrogen bonds) as they move by one another is such that they won't all 'disperse' as individual/free particles, so to speak.

-As a gas, the particles have sufficient energy to overcome the intermolecular interactions associated with a liquid and are now free to move anywhere within the space available (i.e. the gas will not have a fixed volume in general). In this way, if we have a sample of a gas in a container the particles will tend to 'spread out' and conform to the shape of the entire container, with any attractive or repulsive interactions between molecules now minimised. The lack of interaction means that the individual gas particles are very stable and 'happy' on their own! If we were to fill a different shaped or sized container with the same gas, they would diffuse and spread out throughout this area in the same manner.

Take a look at this @mrich .....
http://www.msm.cam.ac.uk/SeeK/graphics/popups/slg.gif

Hope that helped you out!

Answer 2

By the way @mrich .....

\(\bbox[5pt, #33fd33 ,border:5px solid #872af0]{\bf\huge\ Welcome\ to\ OpenStudy!!\ :)}\)

Answer 3

Sorry! I've a small typo in my first sentence of the paragraph about liquids in my original post. It should read:

"A liquid is something which generally we don't associate with having a fixed shape."

Did you figure out which of the four options it is @mrich for the correct answer?