Part 1: Chemical Equations

 How are chemical changes related to macroscopic properties?  How do chemical equations describe chemical reactions?  How are chemical reactions balanced by changing coefficients

 Reactant  Product  Chemical equation  Skeleton equation  Catalyst  Coefficients  Balanced equation

 Chemical reactions occur when one or more substances undergo chemical changes to form new substances  They can be describe with words like: grow, ripen, decay, rust, and burn  They happen all the time, all around you and inside of you  What are some examples?

 They rearrange atoms  Bonds are broken  Bonds are formed

 How are chemical changes different from physical changes?  How are they alike?

 Reactants: the beginning substances  Products : the ending substances  Conservation of Mass & Energy: mass and energy in all chemical reactions is ________ conserved  For example:  2H 2 + O 2 = 2H 2 O

 Production of gas  Color changes  Formation of a ____________-a solid forming out of two liquids combined  Temperature change

 Is indicated by the formation of bubbles  It can happen when two liquids are combined  It can happen when a liquid and a solid are combined

 Can happen when two liquids are mixed  Can happen when a solid and a liquid are mixed

 This can occur when solutions containing ionic compounds are mixed and an insoluble product is formed  The identity of the precipitate can be determined by looking at solubility  It also occurs when one metal ion in solution is replaced by another metal ion.

 An increase or decrease in temperature can indicate a chemical reaction is occurring  It can be detected with a thermometer or by feeling the reaction vessel

 Two main methods of expression:  A word equation  Ex. hydrogen peroxide yields hydrogen gas and oxygen  A chemical equation  Ex. H 2 O 2 H 2 + O 2

 To write a word equation:  Write the names of the reactants on the left of the arrow separated by plus signs  Write the names of the products to the right of the arrow separated by plus signs

1.H 2 O 2 H O 2 2.CH 4 + O 2 CO 2 + H 2 O

1. Fe 2 O 3 + H 2 Fe + H 2 O 2. P + O 2 P 4 O 10

 Is a representation of a chemical reaction using chemical formulas for the reactants and products connected by an arrow and whole numbers to indicate the relative amounts  For example: Fe + O 2 Fe 2 O 3  Equations that show just the formulas of the reactants and the products but do not indicate the relative amounts are called skeleton equations

 Many reactions require the addition of a catalyst to make it proceed in a timely manner  A catalyst is a substance that speeds up a reaction but is not used up in the reaction itself  A catalyst’s symbol or formula is written above the yield arrow

 To write a skeleton equation:  Write the formulas of the reactants to the left of the yields sign and the formulas of the products to the right  To add more information, you can indicate the physical states of the substances  (s) = solid, (l) = liquid, (g) = gas & (aq) = aqueous solution

1.Sodium metal with water yields sodium hydroxide solution and hydrogen gas 2.Hydrogen gas with solid sulfur yields dihydrogen sulfide.

1. Ammonia vapor added to oxygen gas with a catalyst of platinum metal yields nitrogen monoxide gas and water vapor. 2. Aqueous sulfuric acid added to an aqueous solution of barium chloride yields solid barium sulfate and aqueous hydrochloric acid

 Below is an unbalanced chemical equation  Unbalanced chemical equations do not indicate the quantity of the reactants needed to make the product  H 2 O H 2 + O 2

 When we account for the conservation of mass, we create a balanced chemical equation, in which each side of the equation has the same number of atoms of each element  The numbers in front of the chemical formulas are called coefficients, which are small whole numbers that balance an equation  For example:  2H 2 O 2H 2 + O 2

1.Write a skeleton equation 2.Count the atoms 3.Insert coefficients by balancing one element at a time (save hydrogen & oxygen for last) 4.Check and re-check your answers

 Methane combined with oxygen yields carbon dioxide and water  CH 4 + O 2 CO 2 + H 2 O  Reactant side: 1 carbon, 4 hydrogen, 2 oxygen  Product side: 1 carbon, 2 hydrogen, 3 oxygen  What atoms need to be balanced?

 CH 4 + 2O 2 CO 2 + 2H 2 O  Start with hydrogen by adding a two in front of water  Now check and recheck oxygen  Now we have 2 oxygen on one side and four on the other  So, we have to add 2 in front of oxygen on the reactant side  Now check

1.Solid carbon added to oxygen gas yields carbon dioxide gas 2.Zinc (II) nitrate plus dihydrogen sulfide yields zinc (II) sulfide and nitric acid

3.Zinc (II) hydroxide plus phosphoric acid yields zinc (II) phosphate and water 4.Iron (III) chloride + calcium hydroxide yields iron (III) hydroxide and calcium chloride