Tuesday January 5

Characteristics of Chemical Equations

• Word and Formula Equations
• To balance an equation, begin by counting atoms of elements that are combined with atoms of other elements and that appear only once on each side of the equation

CH4 (g) + O2 (g) yields CO2 (g) + H2O (g) not balanced

• Begin by counting carbon atoms
• carbon is already balanced in the equation
• 2 additional hydrogen atoms are needed on the right side of the equation

CH4 (g) + O2 (g) yields CO2 (g) + 2H2O (g)

• now consider the number of oxygen atoms
• increase the number of oxygen atoms on the left side to 4 by placing the coefficient 2 in front of the molecular formula for oxygen
• The correct formula is

CH4 (g) +2O2 (g) yields CO2 (g) + 2H2O (g)

• arrow means "yields"
• two arrows means the equation is reversible
• (s) means the reactant or product is in a solid form
• a downward arrow is an alternative to (s, indicates a precipitate
• (l) is reactant or product in liquid form
• (aq) means it is dissolved in water
• (g) means it is a gas
• Arrow with a triangle or the word heat above it means that heat was added to the reactants
• arrow with the word pressure above it means pressure was applied during the reaction
• arrow with a temperature above it tells the temperature that reaction occured (no temperature is understood to be room temp)
• arrow with a chemical or element above it means that a catalyst was used to increase the rate of the reaction
• arrow with e- under it means electrolysis was used

sifnificance of a chemical equation

• some of the quantitative information revealed by a chemical reaction includes:

1. the coefficients of a chemical reaction indicate relative, not absolute, amounts of reactants and products
2. the relative masses of the reactants and products of a chemical reaction can be determined from the reaction's coefficients
3. the reverse for a chemical equation has the same relative amounts of substances as the forward reaction

• an equation does not indicate a reaction will occur
• an equation gives no info. about the speed of the reaction
• an equation does not give info. about changes in atom and ion bonds

Balancing chemical equations

• the following procedure demonstrates how to master balancing equations by inspection using step-by-step approach

1. Dr. B said it wasn't that important (and i never got it written down)
2. Write a formula equation by substituting correct formulas for the names of the reactants and the products
3. balance the formula equation according to the law of conservation of mass

• balance different types of atoms one at a time
• first balance the atoms of elements that are combined and that appear only once on each side of the equation
• balance polyatomic ions that appear on both sides of the equation as single units
• Balance H and O atoms after atoms of all other elements have been balanced

4. count atoms to make sure equation is balanced

• if the coefficients are not the smallest whole-number ratio, divide by the GCF in order to get the smallest whole-number ratio