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ap chem study guides

🌀  Unit 3 - Intermolecular Forces and Properties

👟  Unit 5 - Kinetics

🔥  Unit 6 - Thermodynamics

⚖️  Unit 7 - Equilibrium

  Unit 9 - Applications of Thermodynamics

🤺  AP Chemistry Essentials

3.3 Solids, Liquids, and Gases

#solids

#liquids

#gases

⏱️  5 min read

written by

kanya shah

Dalia Savy

dalia savy

Dylan Black

dylan black

(editor)

October 7, 2020


Key Terms to Know

  • Fluidity - the ability for molecules to flow past one another

  • Compressibility - a measure of volume change of a substance when pressure is applied

Matter

Let’s look over some of the characteristic properties of the states of matter:

🧊Solids

As we learned in the last key topic, solids can either be crystalline or amorphous. Crystalline solids have a structure and 3D order, while amorphous solids have considerable disorder within their structures.

Regardless of the type of solid, all solids retain their own shape and volume. They don’t expand to fill their container. This is because the particles in a solid are packed very closely together and cannot move.

The intermolecular forces are strong enough to keep the particles in place.

They are virtually incompressible, don’t flow, and the diffusion process within a solid occurs extremely slowly.

💧Liquids

Liquids assume the shape of a portion of the container it occupies. Liquids do NOT expand to fill their container, they just fill the space that is provided by the container.

Since liquid particles aren't tightly packed together, they have the ability to flow past one another (fluidity).

The intermolecular forces are strong enough to hold the molecules closely together, but not strong enough to hold them in place.

Liquids are virtually incompressible, flow readily, and diffusion within a liquid occurs slowly.

Surface Tension

Surface Tension is when molecules on a surface of a liquid experience a net inward force.

The stronger the IMFs, the higher the surface tension.

You see this all the time!

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-R3JKAp4Qs0YH.JPG?alt=media&token=98fdb55d-fcbf-4bc6-90a4-4105eedaf30a

Image Courtesy of Gizmodo

Whenever you turn the sink on at a low pressure, the particles always form a spherical shape. This occurs because of the high surface tension of water as a result of its strong hydrogen bonding (IMFS). Here is a particle representation of surface tension:

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-Hii9f2zPPXZY.png?alt=media&token=780f2255-c100-4e12-bc3d-f6a7585016c3

Image Courtesy of Pinterest

Capillary Action

Capillary action is the spontaneous rising of a liquid. It often happens with polar liquids that have strong IMFs. You could see this when you put a paper towel🧻 in contact with a puddle. The water will slowly rise up the towel due to capillary action.

There are two different types of forces involved:

  • Cohesive Forces: forces between H2O molecules

  • Adhesive Forces: forces between molecules and the container

Remember the typical meniscus (bottom right image) you see when you do experiments? That occurs when the adhesive forces are stronger than the cohesive forces, so the water is more strongly attracted to the graduated cylinder🧪.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-Lr3HnBpMSNZG.png?alt=media&token=9a650160-4b3c-4187-a48d-cb247d08ab46

Image Courtesy of Bartleby

I bet you've never seen Mercury in glass! Well that creates an upside down meniscus, which is called a convex meniscus. This occurs because the forces between the mercury molecules are stronger than the forces between the molecules and the glass (cohesive>adhesive).

Viscosity

Viscosity is a measure of a liquid's resistance to flow. The stronger the IMFs, the higher the viscosity and the thicker the liquid. You see this with syrup🥞.

♨️Gases

Gases assume the volume and shape of their container.

Gas particles move rapidly in straight lines; more about the behavior of gases is covered in the rest of this unit!

The molecules have enough energy to overcome any intermolecular forces that exist, therefore allowing them to move freely.

They are compressible, flow readily, and expand to fill the container. Diffusion within a gas occurs rapidly. 

https://www.schoolsofkingedwardvi.co.uk/wp-content/uploads/2017/07/solid_liquid_gas-768x432.jpg

Image Courtesy of the Schools of King Edward VI in Birmingham

Density

Density measures how compact a substance is! The formula for Density is D = m/V, or density = mass divided by volume.

It is good to remember that solids are usually the most dense out of the three phases and gases are usually the least dense since they flow freely in open space.

Practice Question

The following question is from a Fiveable live stream!

  1. A student measured the mass of a sealed 644 mL flash that contained air. The student then flushed the flask with an unknown gas, resealed it, then measured the mass again. The air and the unknown gas were at STP. Calculate the mass of the unknown gas. The density of air at STP is 1.29 g/L.

Volume of sealed flash644 mL
Mass of Sealed flask and air121.03 g
Mass of Sealed Flask and Unknown Gas122.60 g

Before answering the question, let's note that the air is in a sealed flask. This means that it cannot escape into the atmosphere so the most it could do is fill the shape of the container.

Also, don't worry about STP yet, we'll go over that in the next key topic.

First Step - Find the mass of the air: Since we are given both the density of the air and the volume of the sealed flask, we can find the mass. However, they give us a density in g/L and a volume in mL, so first we have to convert 644 mL into .644 L by simply moving the decimal 3 to the left. D = M/V --> 1.29 = M/.644 --> M = 0.831 g

Second Step - Find the mass of the flask: Since we now know the mass of the air and the mass of both the air and the flask, we can just subtract. 121.03 g - 0.831 g = 120.20 g

Final Step - Find the mass of the unknown gas: They have given us the mass of both the sealed flask and the unknown gas. Since we know the mass of the sealed flask alone, we can just subtract and get our final answer! 122.60 g - 120.20 g = 2.40 g

Overview

To remember the differences between a solid, liquid, and gas, think about your own experiences in life. For example, liquids, like water, will flow freely whereas a solid, like ice, maintains its shape no matter what container it is in. Here's a chart from our states of matter live stream to help out:

https://gyazo.com/2fec37339ea6173f441984278c306b83.png

🎥Watch: AP Chemistry - Solids, Liquids, and Gases

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