SCIENCE (PERIODICZAL)

• Chemical reaction


  1. The properties of the original substance change into new substances with different physical & chemical properties

  2. Chemicals interact to form new chemicals

  3. Reactants are transformed into products
• Reactants


  Substances used to form new substances
• Products


  Resulting substances
• Physical change


  When physical change occurs there is no breaking and forming of bonds
• Evidences of chemical reaction


  • Change of color
  • Formation of gas
  • Temperature change
  • Change in smell
  • Formation of precipitate
• Precipitate


  Cloudy substance that comes out when mixing substances
• George Ernst Stahl


  Formed the phlogiston theory
• Phlogiston theory


  States that when a material burns, it releases a phlogiston
• Antoine Lavoister


  Formed the theory of oxidation
• Theory of oxidation


  1. Debunked the phlogiston theory

  2. Lavoister discovered that instead of releasing a phlogiston, a material burns as if reacts with oxygen

  3. This theory is accepted up to this day
• Factors required for burning


  • Fuel
  • Oxygen
  • Heat
• Chemical equation


  • A chemist shorthand for chemical reaction
  • Distinguishes between the reactant & products
  • Shows the symbols of the reactants or formulas & products, the phases (solid,liquid,gas) of these substances, and the the ratio of the substances they react
• Symbols used in chemical equations


  • + - combination
  • -> - to produce
  • (s) (l) (g) (aq) - solid, liquid, gas, aqueous (substances dissolved in water)
  • -> <- - reversible
  • Pt - a formula written above or below the yield sign indicating its use as a catalyst or solvent
• Combination (synthesis) reaction


  2 or more reactants combined to form a single product
• Decomposition reaction


  A single reactant breaks into simpler ones product
• Single displacement (replacement) reaction


  One element replaces another element from a compound
• Double displacement reaction (metathesis)


  The positive ions (cations) & negative ions (anions) of different compounds switch places forming 2 entirely different compounds
• Combustion (burning) reaction


  Oxygen combines with hydrocarbon a (contains hydrogen & oxygen) to form water, carbon dioxide
• Acid-base reaction


  • Double displacement reaction
  • Acid and base react with each other
  • H+ of the acid reacts with the OH- of the base forming water
  • The other product is salt (NaCl)
• Subscripts


  Shows how many atoms an element have in a molecule
• Coefficient


  Shows how many molecules are there in a particular chemicals
• Law of conservation of mass: states that mass is conserved in a chemical reaction, the total mass of the reaction is equal to the total mass of the products, no new atoms are created nor destroyed, there is only groupings or re-groupings of atoms
• Steps in balancing equations


  1. Take note of the elements present in the reactants & products side

  2. Count the number of atoms in each element present in the reactant and product side

  3. Apply the law of conservation of mass to get the same number of atoms on every element on each side of the equation

  4. Balance chemical equations by placing the appropriate coefficients before the symbol or formula

  5. Do not change the subscripts of the formula in an attempt to balance the equation as it will change the identity of the components