Topic 2

• Gases are composed of molecules
• Gas molecules are always in constant random motion and they frequently collide with one another and with the walls of the container.
• There is neither attractive nor repulsive force between or among gas molecules
• 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.
• 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 and it is accepted up to this day.
• Chemical equation - Describes a chemical change
• Parts of an equation are  Reactant & Product
• 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

  • EX: H2O

  • 2 atoms of hydrogen (H)‏

  • 1 atom of oxygen (O)‏
• Coefficient - shows how many molecules there are of a particular chemical

  • EX: 3 H2O

  Means there are 3 water molecules of water
• 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.
• Rules of the Game

  1. Matter cannot be created or destroyed.

  2. Subscripts CANNOT be added, removed, or changed.

  3. You can ONLY CHANGE coefficients.

  4. Coefficients can only go in front of chemical