Interactive Site Practice:

http://www.sciencebugz.com/chemistry/chprbbaleq.html
 
http://chemistry.csudh.edu/lechelpcs/rxnbalancingcsn7.html
 
http://www.files.chem.vt.edu/RVGS/ACT/notes/scripts/bal_eq1.html
 
http://education.jlab.org/elementbalancing/index.html

 

 

Balancing Chemical Equations

 

A. Equations show:

  1. The reactants are the substances which enter into a reaction.
  2. The products are the substances which are formed by the reaction.
  3. The amounts of each substance used and each substance produced.

B. Two important principles to remember:

  1. Every chemical compound has a formula which cannot be altered.
  2. A chemical reaction must account for every atom that is used. This is an application of the Law of Conservation of Matter (mass) which states that in a chemical reaction atoms are neither created nor destroyed.

There are essentially three steps to the process:

1.              Write the unbalanced equation.

·   Chemical formulas of reactants are listed on the lefthand side of the equation.

·   Products are listed on the righthand side of the equation.

·   Reactants and products are separated by putting an arrow between them to show the direction of the reaction. Reactions at equilibrium will have arrows facing both directions.

2.              Balance the equation.

·   Apply the Law of Conservation of Mass (matter) to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only one reactant and product.

·   Once one element is balanced, proceed to balance another, and another, until all elements are balanced.

·   Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.

·   The coefficient in a chemical formula is the number immediately preceding the compound. It appears full size, never as a subscript or superscript. The coefficient is multiplied throughout the formula to which it is attached (in front of).

 

 

 

3.  Indicate the states of matter of the reactants and products.

·   Use (g) for gaseous substances.

·   Use (s) for solids.

·   Use (l) for liquids.

·   Use (aq) for species in solution in water.

·   Write the state of matter immediately following the formula of the substance it describes.

Types of Chemical Equations:

1.  Synthesis Reaction:  two or more simple substances combine to form a more complex substance. Two or more reactants yielding one product is another way to identify a synthesis reaction.
The chemical equation for this synthesis reaction looks like:
synthesisimage
reactant + reactant -------> product

2. Decomposition Reactions: a more complex substance breaks down into its more simple parts. One reactant yields 2 or more products. Basically, synthesis and decomposition reactions are opposites.
The chemical equation for this decomposition reaction looks like:
decomposeimage
reactant -------> product + product

3.  SINGLE REPLACEMENT REACTION: a single uncombined element replaces another in a compound. Two reactants yield two products.

The chemical equation for this single replacement reaction looks like:
singlereplaceimage
reactant + reactant ---------> product + product

4.  DOUBLE REPLACEMENT REACTION: parts of two compounds switch places to form two new compounds. Two reactants yield two products.

The chemical equation for this double replacement reaction looks like:
doublereplaceimage
reactant + reactant ---------> product + product

Reminder---

1.     Endothermic reactions absorb heat energy.

2.     Exothermic reactions release heat energy.

3.     Equation for Photosynthesis: 

                    6CO2 + 6H2O + Energy →   C6H12O6 + 6O2

4.      Equation for Cellular Respiration: 

                    C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy