Gases

• What are GASES?


  A substance (such as oxygen or hydrogen) that is like air and it has no fixed shape.
• Mass is the amount of matter an object contains, while volume is how much space it takes.
• The particles in a gas move quickly in all directions, but they don't get far before they bump into each other or the walls of their container. When gas particles hit the walls of their container they cause pressure.
• Gases have mass, volume, temperature and pressure because gas is a matter its just that the particles of gases are far from each other compared to those particles in solids and liquids
• Gases do not have a fixed volume or shape.
• Gases are compressible unlike Liquid and Solid.
• It’s volume changes in response to changing pressure.
• Pressure in a closed container changes if

  1. temperature changes
  2. number of molecules increases or decreases
  3. volume changes
• the pressure is increased, the volume decreases.
• the volume of a fixed amount of gas is inversely proportional to its pressure at constant temperature
• Boyle’s Law States that:

  For a fixed amount of gas at constant temperature, the volume of the gas is inversely proportional to its pressure
• Charles’ Law: states that at a constant pressure, the volume of a fixed amount of gas is directly proportional to the Kelvin (K) temperature
• Gay – Lussac’s Law states that:

  At constant volume, the pressure of a fixed mass of gas is directly proportional to the absolute temperature.
• Combined Gas Laws states that:

  The pressure and volume of a gas are inversely proportional to each other, but are both directly proportional to the temperature of that gas.
• Mole -  the base unit of amount of pure substance in the International System of Units that contains the same number of elementary entities as there are atoms in exactly 12 grams of the isotope carbon 12
• The volume of a gas is directly proportional to the number of moles of gas present at a given temperature and pressure.
• Ideal Gas Law - Relation between the pressure , Volume , and temperature of a gas in the limit of low pressure and high temperatures, such that molecules of the gas move almost independently of each other.
• Ideal Gas Law - Volume is directly proportional to number of moles and temperature but inversely proportional to pressure.
• Kinetic Molecular Theory  (KMT) states that:

  A. Gases are composed of molecules

  B. Gas molecules are always in constant random motion and they frequently collide with one another and with the walls of the container.

  C. There is neither attractive nor repulsive force between or among gas molecules.

  D. Movement of gas molecules is affected by temperature> The average kinetic of the molecules is directly related to the temperature of gas.
• Gases have mass, volume, temperature and it exerts pressure. The pressure exerted by gas molecules is due to collision among gas molecules and with the walls of the container. The frequency of collision is affected by temperature because gas molecules move faster at high temperature, on the other hand, they move slowly at low temperature. The faster the movement of the molecules, the more frequent the collision, causing an increase in pressure.
• Substances undergo chemical bonding so that atoms can become more stable. Chemical bonding results to breaking of bonds and formation of new bonds, thus new substances are formed. Formation of new substances means chemical reaction has taken place.

   
• When Physical Change occurs, there is no breaking and forming of bonds.
• Evidences of chemical Reactions:

  1. Production of light

  2. Evolution of gas

  3. Temperature change

  4. Change in intrinsic properties (color, odor)

  5. Formation of precipitate
• Phlogiston Theory  by George Ernst Stahl stated that when a material  burns, it releases a substance known as Phlogiston.
• Antoine Lavoisier debunked the Phlogiston theory as he discovered that instead of releasing a substance (Phlogiston) a material accurately burns as it reacts with oxygen. This is known as Theory of Oxidation
• Chemical equation - Describes a chemical change
• Reactant - The chemical(s)/element(s) you start with before the reaction occurs
• • Product The new chemical(s)/elements formed by the reaction
• Subscript - shows how many atoms of an element are in a molecule
• Coefficient - shows how many molecules there are of a particular chemical
• Law of Conservation of Mass

  In a chemical reaction, matter is neither created nor destroyed. In other words, the number and type of atoms going INTO a reaction MUST be the same as the number and type of atoms coming OUT. If an equation obeys the Law of Conservation, it is balanced.