HGE 1115: Physical Science

• Rate of Chemical Reaction - the speed at which a chemical reaction proceeds
• Collision Theory - for reactions to occur, molecules, atoms, or ions must first collide
• Reactants must be in proper orientation
• Molecules must possess minimum amount of energy
• if the temperature of a reaction system is increased, the average speed of the particles is also increased.
• an increase in reactant concentration means that there will be more collisions between particles.
• The greater the surface area, the greater frequency of collisions between reacting particles; hence, the faster the reaction.
• Catalyst - This allows the reaction to occur in an alternative pathway
• The Catalyst pathway requires lower activation energy.
• stoicheion - element
• metron - measure
• Stoichiometry - deals with calculations about the masses (sometimes volumes) of reactants and products involved in a chemical reaction.
• 2H₂ is a Coefficient

  
• 2H₂+O₂ are reactants

  
• 2H₂O is a product

  
• Reactants appear on the left side of the equation
• Product appears on the right side of the equation
• The states of the reactants and products are written in parentheses to the right of each compound
• Coefficients are inserted to balance the equation
• Subscripts tell the number of atoms of each element in a molecule
• Coefficients tell the number of molecules
• Law of Conservation of Mass - states that mass cannot be created or destroyed in a chemical reaction
• Unbalanced Equation

  
• Steps to Balancing a Chemical Equation

  1. Write all reactants on the left and all products on the right side of the equation arrow.
  2. Use coefficients in front of each formula to balance the number of atoms on each side.
  3. Multiply the coefficient of each element by the subscript of the element to count the atoms. Then list the number of atoms of each element on each side.
  4. Balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.
• Chemical Reaction - It is a chemical change in which one or more substances are destroyed and one or more new substances are created
• Reactants - Substances that are destroyed by the chemical change (bonds break).
• Products - Substances created by the chemical change (new bonds form).
• The arrow (->) is read as “yields”.
• (s) = solid (l) = liquid (g) = gas
• (aq) = aqueous solution (the substance is dissolved in H2O
• “+” separates two or more reactants or products
• “->” yield sign separates reactants from products
• Evidences for Chemical Reactions

  1. Evolution of Light or Heat
  2. Temperature Change (Increase or Decrease) to the surroundings
  3. Formation of a gas (bubbling or an odor) other than boiling.
  4. Color change (due to the formation of a new substance).
  5. Formation of a precipitate (a new solid forms) from the reaction of two aqueous solutions.
• Word Equations - Statements that indicate the reactants and products in a chemical reaction.
• A skeleton equation uses chemical formulas rather than words to identify the reactants and products of a chemical reaction.
• A skeleton equation is not yet “balanced” by coefficients
• Not All Properties are ConservedDuring Chemical Reactions
• Properties Conserved

  • Mass
  • Types of Atoms
  • Number of Each Atom
• Properties Not Conserved

  • Color
  • Physical State (Solid, Liquid, Gas)
  • Volume
  • Number of Moles of Reactants/Products
• Types of Chemical Reactions

  • Single Replacement (Displacement) (Redox)
  • Double Replacement (Displacement) (Metathesis)
  • Synthesis (Combination)
  • Decomposition
  • Combustion