MELC 21

• Gas - derived from the Greek term "chaos", which means formless mass.
• • Gas is a state of matter that has indefinite shape, size, and no fixed volume. It’s fit the shape and size of their container.
  • Gases have a lower density than other states of matter, such as solids and liquids.
• • There is a great deal of empty space between particles, which have a lot of kinetic energy and aren’t particularly attracted to one another.
  • Gas particles move very fast and collide with one another, causing them to diffuse, or spread out until they are evenly distributed throughout the volume of the container.
• expansibility - the property of gases to expand (increase the spaces between its molecules) when heated and contract when cooled.
• compressibility - its ability to compress when pressure is exerted, and they also exert pressure.
• diffusibility - its ability to diffuse or intermingle with the molecules of other substances. The intermolecular force of attraction between their particles is negligible, thus, they diffuse easily.
• fluidity - because the attractive forces between gas particles are slight, gas particles glide past one another. They flow just like liquids.
• density - The density of a substance in the gaseous state is about 1/1000 the density of the same substance in the liquid or solid state. That is because their particles are so spread out and far apart from each other.
• kinetic molecular theory of gases - explains why gases behave as they do. It deals with ideal gas particles.
• An ideal gas is defined as one in which all collisions between atoms or molecules are perfectly elastic (no energy is lost) and in which there are no intermolecular attractive forces.
• Gases consist of large numbers of tiny particles that are far apart relative to their size.

  • Most of the volume occupied by a gas is empty space.
  • Accounts for lower density compared to solid and liquids.
• Collisions between gas particles and between particles and container walls are elastic collisions with NO loss of energy.
• Gas particles are in constant, rapid, random motion—They possess kinetic energy.
• There are no forces of attraction or repulsion between gas particles.
• The average kinetic energy of gas particles depends on the temperature of the gas. 

  • All gases at the same temperature have the same average kinetic energy.
• The volume of a gas is equal to the volume of its container.
• The temperature of a gas is the average kinetic energy of the particles of gas. It is usually determined using a thermometer. It is usually expressed in degree Celsius (°C), degree Fahrenheit (°F) and Kelvin (K).
• • The standard temperature is the melting of an ice which is 0°C or 273K. 
  • The standard pressure is the average pressure of the atmosphere at sea level which is equal to 1 atm. 
  • One mole of gas occupies a volume of 22.4 L.
• Robert Boyle - was the first to investigate the relationship between the pressure of a gas and its volume. 
• • Boyle concluded that pressure is inversely related to volume such that when the pressure is doubled, the volume of the gas is decreased to half its original value.
• Boyle’s Law states that

  • the pressure of a gas is inversely related to its volume when T and n are constant.
• • if volume decreases, the pressure increases.
• boyle's law formula - P1V1 = P2V2