Chapter 6: Chemical Reactions

1
Chapter 6 Chemical Reactions
Chemistry 1020 Interpretive chemistry Andy
Aspaas, Instructor
2
Chemical reactions

• Chemical reaction a chemical change in which a
  new substance is formed
• Clues that a chemical reaction has occurred
• Color change, solid forms, bubbles form,
  heat/flame produced, heat absorbed
• But, clues are not absolute - physical changes
  can sometimes produce those observations
• Chemical reactions involve rearrangement of atoms
  to form new substances

3
Chemical equations

• Reactants chemicals present before a reaction
• Products chemicals present after a reaction
• Chemical equation representaton of a chemical
  reaction
• Reactants ? Products
• CH4 O2 ? CO2 H2O
• Only carbon, hydrogen, and oxygen exist on both
  sides of equation

4
Writing and interpreting chemical equations

• The ? in a chemical equation means produces or
  yields or reacts to form
• Physical states can also be indicated in a
  chemical reaction
• (s) solid, (l) liquid, (g) gas,
• (aq) aqueous (dissolved in water)
• K(s) H2O(l) ? H2(g) KOH(aq)
• But, this equation is unbalanced (different
  quantities of atoms on each side of equation)

5
Balancing chemical equations

• CH4 O2 ? CO2 H2O is unbalanced
• Reactants 1C, 4H, 2O
• Products 1C, 2H, 3O
• Law of conservation of mass atoms must be
  neither created nor destroyed in a chemical
  reaction
• Coefficients are added to balance the equation
• Whole numbers before a compound that indicates
  quantity
• Ex. 2H2O means there are 2 water molecules present

6
Balancing chemical reactions

• Start with an unbalanced equation
• Start with the most complicated molecule and add
  coefficients so that the number of atoms it
  contains equals the number of those same atoms on
  the other side of the equation
• Proceed balancing other elements
• Check your work by totaling all the atoms on each
  side - the totals for the two sides should be
  identical

7
Practice balancing

• CH4(g) O2(g) ? CO2(g) H2O(g)
• K(s) H2O(l) ? H2(g) KOH(aq)
• C2H5OH(l) O2(g) ? CO2(g) H2O(g)
• (start with C)
• NH3(g) O2(g) ? NO(g) H2O(g)