Reactions in Chemistry Writing Balanced Chemical Equations
Writing reaction equations Before you can write a balanced chemical equation for a reaction, you need to write an unbalanced equation. To do this you need to identify several things: What chemicals are reacting? What is the proper formula for each chemical? What type of reaction is it? What are the products that will be produced? What are their proper formulas?
Types of chemical reactions Remember, the five basic categories of reactions are: Synthesis (a.k.a. Direct Combination) Decomposition
Types of chemical reactions Single Replacement Double Replacement
Types of chemical reactions Combustion An element or compound reacts with oxygen, often producing energy in the form of heat and light. If a hydrocarbon undergoes combustion, the products are normally CO2 and water.
Things to remember When writing the chemical formulas: Hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine are diatomic molecules. When deciding on formulas for binary ionic compounds, use the crisscross method and remember to reduce the ratio of atoms if possible. Be sure that all chemical formulas are correct and that all reactants and products have been included before trying to balance the equation.
Example 1 A strip of magnesium is placed in a hydrochloric acid solution, and hydrogen gas is released. Write a balanced equation for the reaction that takes place. What are the reactants? What are their formulas? Magnesium metal and hydrochloric acid. Mg and HCl
Example 1 (cont) What type of reaction would this be? What are the products? (Were all of them mentioned?) What are their formulas? Single replacement Magnesium chloride and hydrogen gas. MgCl2 and H2
Example 1 (cont) What would the unbalanced equation be? Now balance it: Reactants Products Mg – Mg – H – H – Cl – Cl –
Example 2 Potassium chlorate decomposes, to evolve oxygen. What are the reactants? What are their formulas? Only potassium chlorate KClO3
Example 2 (cont) What type of reaction would this be? What are the products? (Were all of them mentioned?) What are their formulas? Decomposition Oxygen and potassium chloride O2 and KCl
Example 2 (cont) What would the unbalanced equation be? Now balance it: Reactants Products K – K – Cl – Cl – O – O –
Example 3 Copper(II) sulfate reacts with a sodium hydroxide solution. What are the reactants? What are their formulas? Copper(II) sulfate and sodium hydroxide. CuSO4 and NaOH
Example 3 (cont) What type of reaction would this be? What would the products be? What are their formulas? Double replacement Copper(II) hydroxide and sodium sulfate Cu(OH)2 and Na2SO4
Example 3 (cont) What would the unbalanced equation be? Now balance it: Reactants Products Cu – Cu – SO4 – SO4 – Na – Na – OH – OH –
Example 4 The reaction that takes place in a butane lighter. (butane is C4H10) What type of a reaction is this? What would the reactants be? Burning would indicate combustion Butane and oxygen
Example 4 (cont) What are the formulas for the reactants? What would the products be? What are their formulas? C4H10 and O2 Combustion results in carbon dioxide and water CO2 and H2O
Example 4 (cont) What would the unbalanced equation be? Now balance it: Reactants Products C – C – H – H – O – O –
Example 5 Soda pop gets its acidic taste because as carbon dioxide is forced to dissolve in the pop, it combines with water forming an acid. What type of a reaction is this? What would the reactants be? Synthesis (or direct combination) Carbon dioxide and water
Example 5 (cont) What are the formulas for the reactants? What would the products be? What are their formulas? CO2 and H2O Synthesis results in only one product. In this case it would be carbonic acid. Only H2CO3
Example 5 (cont) What would the unbalanced equation be? Now balance it: Reactants Products C – C – O – O – H – H –
Resources: http://wps.prenhall.com/wps/media/objects/16 5/169519/GIFS/AAAUAUH0.JPG http://reich- chemistry.wikispaces.com/file/view/hcl3.gif/32 672567/hcl3.gif http://www.eatlikenoone.com/wp- content/uploads/2010/01/CocoFizz.JPG