Chapter 3 States of Matter

3.1 Solids, Liquids, & Gases States of Matter (we will study 3) Materials can be classified as solids, liquids, or gases based on whether their shapes & volumes are definite or variable. There are forces of attraction among the particles in all matter. Definite – means that the shape and volume of the object won’t change as you move it. It doesn’t mean that the shape or volume can never change.

Solids Have a definite shape and definite volume. Particles rotate or vibrate around fixed locations. Particles cannot exchange places with another atom.

Liquids Have a definite volume but not a definite shape. Variable shape – takes on the shape of the container. Particles move or slide past each other. Forces of attraction keep the particles close together.

Gases Neither a definite shape nor definite volume; both are variable Takes on the shape and volume of the container. Particles move all around in constant motion Can be compressed (pushed together).

On Earth, almost all matter exists as a solid, liquid, or gas. 99% of the matter in the universe exists as the state of matter called “plasma.” Extremely high temperatures make matter exist like this on the sun or the other stars. A 5th state exists, known as Bose-Einstein condensate (BEC). At extremely cold temperatures(-273 ̊C), groups of atoms would behave as though they were a single particle. Einstein predicted this in the 1920s.

Why is copper a solid, mercury a liquid and helium a gas? This is all explained kinetic energy. All matter has particles that are moving inside the object. The faster an object moves the greater its kinetic energy. The kinetic theory of matter says that all particles of matter are in constant motion.

Explaining the Behavior of Gases: Motion in Gases The particles in a gas are never at rest. The average speed of the particles in a sample of gas is about 1600 Km/hr. Remember this does not mean all the particles of gas are moving at the same speed (it is an average). When 2 atoms collide one atom might slow down and lose KE but the other atom will gain KE and speed up. Therefore, the total KE remains the same.

The problem with gases is that the gas particles are very far apart from each. There are forces of attraction among all particles in nature. However, sometimes the particles, like in a gas, are so far apart and moving so fast that the attractions are too weak to have any effect. Therefore, under ordinary conditions scientists ignore the forces of attraction in a gas.

Kinetic Theory of Gases The kinetic theory explains the general properties of a gas. There are 3 main points 1. Particles in a gas are in constant, random motion. 2. The motion of one particle is unaffected by the motion of other particles unless the particles collide. 3. Forces of attraction among particles in a gas can be ignored under ordinary conditions.

Explaining the Behavior of Liquids The particles in a liquid also have KE. However, the particles in a liquid have a definite volume. Also, the particles in a liquid are more closely packed together. Therefore, the movement of the particles are affected by the interactions between the particles.

There is a tug of war between the constant motion of particles and the attractions among particles in a liquid. These forces of attraction limit the motion of particles in a liquid, and do not let them spread out and fill the container.

Explaining the Behavior of Solids Solids particles are in an orderly arrangement. The particles can vibrate and rotate in a repetitive motion. They have a definite volume and shape because of the particles staying in their fixed position.

Section 3.2 The Gas Laws Pressure- is the result of a force distributed over an area. The SI unit for pressure is the Pascal (Pa) it means newtons per square meter (N/m2). This comes from the SI units of force and area. Scientists often use kilopascals (kPa) to measure pressure because one pascal is a small amount of pressure (1 kPa = 1000 Pa)

Collisions between particles of a gas and the walls of the container cause the pressure in a closed container. The more frequent collisions the gas particles have the greater the pressure of the gas. Speed of the gas particles and their mass also affects the pressure.

Factors That Affect Gas Pressure There are 3 factors that affect the pressure of an enclosed gas. 1. Temperature: Raising the temperature of a gas will increase its pressure if the volume of the gas and the number of particles are constant. Volume: Reducing the volume of a gas increases its pressure if the temperature of the gas and the number of particles are constant.

3. Number of Particles: Increasing the number of particles will increase the pressure of a gas if the temperature and the volume are constant. Basically what you just learned is that there are 4 factors that are used to understand how gases behave- pressure, volume, temperature and the number of particles. These 4 variables are used in the gas laws to understand how gases work.