Chemistry Unit 7

• Physical Changes

  Substances often undergo changes that make them have a dramatically different appearance, even though the chemical composition of the substance remains unchanged.
• Physical changes


  A change, which alters a substance's appearance without changing its chemical composition, is known as a physical change

  • Temporary and reversible
  • There is no change in identity of the substance (original identity not lost)
  • Ex: melting, chopping, hammering, appearance change
• Chemical change

  A change where a substance loses its identity and produces one or more substances by change in its chemical composition.

  • Permanent change
  • Happens due to forming/breaking of chemical bonds
  • New substances are formed that have different identity and properties than the original substances
  • Ex: Burning, cooking, rusting, oxidation, tarnishing
• Reactants

  Substances that enter into a chemical reaction an are always written on the left side of the chemical equation.
• Product

  Substances produced in a chemical reaction and are always written on the right side of the chemical equation.
• The arrow (-->) is yield
• (s)= solid

  (l)= liquid

  (g)= gas

  (aq)= aqueous

  Triangle = heated

   ⇌ = reversible reaction
• Aqueous

  A solution where the water is solvent (dissolvable in water)
• Aqueous solution is a mixture.
• Balance in chemical equations

  Chemical equations need to be balanced so that it follows the law of conservation of mass.

  • Mass of reactant=mass of product
  • A balanced chemical equation occurs when the number of the different atoms of elements in the reactants side is equal to that of the products side
  • When balancing a chemical equation, the chemcial formulas for the substances are never changed. Instead, coefficients are used in the smallest ratio possible.
• Coefficient

  Whole numbers added in front of reactant or product in a chemical equation

  • The "1" is assumed
  • Subscript indicates number of atom of each element in a given formula
  • Indicates the number of mole/molecules/atoms in a given formula
• Synthesis Reaction


  2 or more simple substances combine to form a complex substance. 2 or more reactants combine to yield 1 product.

  • A + B --> AB
  • Ex: K + S → K2S SO2 + O2 → SO3
• Decomposition Reaction


  A more complex substance breaks into simpler substances. 1 reactant yields 2 or more products.

  • AB --> A + B
  • Ex: KClO3 → KCl + O2
• Combustion Reaction


  Oxygen combined with hydrocarbon to form water and carbon dioxide.

  • Hydrocarbon= compound it hydrogen and carbon
  • Always exothermic
  • CAHB → H2O + CO2 + heat
  • Ex: CH4 → H2O + CO2 C2H6  → H2O + CO2
• Single replacement reactions


  A single uncombined element replaces another element in a compound.

  • Element + compound --> element + compound
  • Activity series: The higher the element, it will replace the elements lower than it
  • A + BC --> B + AC
  • Ex: Cu + AgNO3  → Ag +  Cu(NO3) 2 Zn  +  HCl  → H2  + ZnCl2
• Double replacement reactions


  Parts of 2 compounds switch places to form 2 new compounds.

  • Compound + compound --> compound + compound
  • AB + CD --> CB + AD
  • Ex: Li2O  +  BeF2→ BeO + LiF
• Balancing formulas

  Br I N Cl H O F

  These have 2 subscript when making the products
• aqueous + solid = reaction

  aqueous + aqueous = no reaction
• lower than (on activity series) = no reaction
• Reactions between an element (metal or halogen) and a compound (aqueous solution) to produce a different element (a metal, halogen gas, or a halogen) and a different compound.
• Law of conservation of mass


  Reactant mass = Product mass