Understanding States of Matter and Thermodynamic Processes

The Four Fundamental States of Matter

• Solid: Characterized by structural rigidity and resistance to changes of shape or volume.
• Liquid: A form of matter between a gas and a solid that has a definite volume but no definite shape.
• Gas: An air-like fluid substance which expands freely to fill any space available, irrespective of its quantity.
• Plasma: A state of matter made from a gas that has lost its electrons due to heat (e.g., the Sun, stars, lightning).

Particle Arrangement

• Solid: Particles are tightly packed, usually in a regular pattern. Solids vibrate (jiggle) but generally do not move from place to place.
• Liquid: Particles are close together with no regular arrangement. They vibrate, move about, and slide past each other.
• Gas: Particles are well-separated with no regular arrangement. They vibrate and move freely at high speeds.
• Plasma: A hot ionized gas consisting of approximately equal numbers of positively charged ions and negatively charged electrons.

Particle Movement

• Solid: Does not flow easily; particles cannot move or slide past one another (rigid).
• Liquid: Not easily compressible; little free space exists between particles.
• Gas: Compressible; lots of free space exists between particles.

Endothermic vs. Exothermic Reactions

An endothermic reaction depends on taking in heat to proceed; therefore, heat is absorbed. The opposite is an exothermic process, in which energy is released in the form of heat.

Endothermic Processes

One of the most common examples of an endothermic reaction is photosynthesis, the process wherein plants use sunlight to produce food and energy. In this case, the energy taken in is light energy from the sun.

Exothermic Processes

An example of an exothermic process is the formation of ice cubes.

Factors Affecting Boiling Point

Pressure:

• When external pressure is less than one atmosphere, the boiling point of the liquid is lower than its normal boiling point.
• When external pressure is equal to one atmosphere, the boiling point of a liquid is called the normal boiling point.

Summary of Heat Exchange

• Endothermic: A reaction or process which absorbs heat from its surroundings (feels cold).
• Exothermic: A reaction or process which gives off heat to its surroundings (feels hot).

Gas Behavior

How gas responds to changes in temperature, pressure, and volume:

Temperature