Chapter 3 Notes – States of Matter
Section 3.1 – Solids, Liquids, and Gases
Materials can be classified as solids, liquids, or gases based on whether their shapes and volumes are definite or variable.
Solid – a state of matter in which materials have a definite shape and a definite volume
-The term definite means that the shape or volume of a pencil will not change as you move it from a desk to your backpack. However, the term definite doesn’t mean that the shape or volume of that pencil can never change. After all, you can change the shape of a pencil by sharpening it.
-The arrangement of molecules in a solid is pictured below.
Liquid – a state of matter in which a material has a definite volume but not a definite shape.
-A liquid always has the same shape as it container and can be poured from one container to another.
-The arrangement of molecules in a liquid is pictured below.
Gas – a state of matter in which a material has neither a finite shape nor a definite volume.
-A gas takes the shape and volume of its container.
-If you picture a balloon, the shape of the helium gas is the same as the shape of the balloon itself. The volume of the helium in a balloon is equal to the volume of the balloon.
-The arrangement of molecules in a gas is pictured below.
Plasma – a state that exists extremely high temperatures
-99% of all matter that can be observed in the universe exists in a state that is not common on Earth.
Kinetic Energy – the energy an object has due to its motion
-The faster an object goes, the greater its kinetic energy.
-According to the kinetic theory of matter, particles inside a moving baseball are moving along with the particles of air that the baseball is traveling through.
-Kinetic theory of matter says that all particle of matter are in constant motion.
Explaining the Behavior of Gases
Particles of gas are never at rest. At room temperature, the average speed of particles is about 1600 km per hour. The use of the word average means that some particles are moving faster than others.
Particles of gas can collide into one another. When that happens, it is possible for one of the particles to become faster while the other slows down.
The constant motion of particles in a gas allows a gas to fill a container of any shape or size.
There are three main points to the kinetic theory. They are…
- Particles in a gas are in constant, random motion.
- The motion of one particle is unaffected by the motion of other particles unless the particles collide.
- Forces of attraction among the particles in a gas can be ignored under ordinary conditions.
Explaining the Behavior of Liquids
The particles of a liquid are more closely packed than the particles in a gas. Therefore, attractions between the particles in a liquid do affect the movement of the particles.
* A liquid takes the shape of its container because particles in a liquid can flow to new locations. The volume of a liquid is constant because forces of attraction keep the particles close together.
Explaining the Behavior of Solids
Solids have a definite volume and shape because particles in a solid vibrate around fixed locations.
For example, you might compare the particles in a solid to a polite audience in a movie theater. While the move is running, people stay in their seats. Although people are moving around in their seats, each person remains in essentially the same location during the movie.
Section 3.2 – The Gas Laws
Pressure – the result of a force distributed over an area
-Collisions between particles of a gas and the walls of the container cause the pressure in a closed container. The more frequent the collisions, the greater the pressure of the gas is. The speed of the particles and their mass also affect the pressure.
Factors That Affect the Gas Pressure
Factors that affect the pressure of an enclosed gas are its temperature, its volume, and the number of its particles.
Raising the temperature of a gas will increase its pressure if the volume of a gas and the number of particles are constant.
-When you check the pressure of your tires before a long road trip, the pressure will be normal. If you check the pressure of the tires after driving on the highway for 4 hours the pressure of the tires will have increased because the constant motion of the tires causes the air in the tire to warm up. Therefore, the kinetic energy of the particles move faster causes more collisions with the inner walls of the tire and hits the walls with a greater force. This increases the pressure.
Reducing the volume of a gas increases its pressure if the temperature of the gas and the number of particles are constant.
* Read page 77 together!!
Increasing the number of particles will increase the pressure of a gas if the temperature and the volume are constant.
Charles’s Law – the volume of a gas is directly proportional to its temperature in kelvins if the pressure and the number of particles of gas are constant.
Boyle’s Law – the volume of a gas is inversely proportional to its pressure if the temperature and the number of particles are constant.
Section 3.3 – Phase Changes
Phase Change – the reversible physical change that occurs when a substance changes from one state of matter to another.
-Melting, freezing, vaporization, condensation, sublimation, and deposition are six common phase changes.
-One way to recognize a phase change is by measuring the temperature of a substance as it is heated or cooled. The temperature of a substance does not change during a phase change.
Energy is either absorbed or released during a phase change.
During an endothermic change, the system absorbs energy from its surroundings. For example, when sunlight shines directly onto an ice sculpture the ice begins to melt.
During an exothermic change, the system releases energy to its surroundings.
Melting and Freezing
When molecules melt they become less orderly and when they freeze they become more orderly.
-When an ice cube sits out on the table, heat flows from the air to the ice which causes the molecules to speed up. When all the molecules have enough energy to move, the ice has melted and the temperature rises.
-When the liquid is placed into the freezer, energy flows from the water to the air in the freezer and the molecules begin to lose energy. When the molecules lose enough energy to simply vibrate, freezing has occurred and the temperature has dropped.
Vaporization–the phase change in which a substance changes from a liquid into a gas. Vaporization is an endothermic process. A substance must absorb energy in order to change from a liquid to a gas.
Evaporation – the process that changes a substance from a liquid to a gas at temperatures below the substance’s boiling point
When water boils, the temperature increases and water molecules move faster and faster. This also means that the pressure increases because of the collisions that the particles are occurring. .
-The boiling point of a substance depends on the atmospheric pressure.
Condensation – phase change in which a substance changes from a gas or vapor to a liquid
For example, when you come out of the shower to find your bathroom mirror clouded over. The fog on the mirror is caused by water vapor that cooled as it came in contact with the mirror.
Sublimation – the phase change in which a substance changes from a solid to a gas or vapor without changing to a liquid first
An example of sublimation is dry ice. Dry ice can change directly from a solid to a gas.
Deposition – when a gas or vapor changes directly into a solid without first changing to a liquid
-Deposition is what causes frost on your windows and is an exothermic phase change. When water vapor in the air comes in contact with cold window glass, the water vapor loses enough kinetic energy to change directly from a gas to a solid.