Stimulants are substances that enhance neural activity and elevate dopamine levels in the brain, leading to their highly addictive nature. These drugs include cocaine, amphetamines, MDMA, caffeine, and nicotine, each with distinct mechanisms of action and varied health implications.
Cocaine can be administered via snorting, injection, or smoking. It primarily functions by blocking the reuptake of dopamine, resulting in a euphoric high characterized by an intense sensation of happiness and...

The physical form of a substance changes by changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize (convert into vapor). The process is called vaporization—a surface phenomenon. For vaporization to occur, kinetic energy must be greater than the intermolecular forces that keep molecules bonded. The amount of energy needed to vaporize a quantity of liquid at a given pressure and a constant temperature is called the heat of vaporization. When...

Overview

The respiratory system is comprised of the organs that enable breathing. Air enters the nostrils and mouth, followed by the pharynx (throat) and larynx (voice box), which lead to the trachea (windpipe). In the thoracic cavity, the trachea splits into two bronchi that allow air to enter the lungs. The bronchi split into progressively smaller bronchioles and terminate in small groups of tiny sacs in the lungs called alveoli, where gas exchange occurs.

When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules move randomly about, they will occasionally collide with the surface of the condensed phase, and in some cases, these collisions will result in the molecules re-entering the condensed phase. The change from the gas phase to the liquid is called condensation. When the rate of condensation becomes equal to the rate of vaporization, neither the amount of the liquid nor the amount of the vapor...

The equilibrium vapor pressure of a liquid is the pressure exerted by its gaseous phase when vaporization and condensation are occurring at equal rates: