Chemical Reactions Slide 3 / 142 Table of Contents: Chemical - PDF document

Slide 1 / 142 Slide 2 / 142 Chemical Reactions Slide 3 / 142 Table of Contents: Chemical Reactions Chemical Equations Click on the topic to go to that section · · Balancing Equations · Types of Chemical Reactions · Precipitation Reactions · Net Ionic Equations · Oxidation-Reduction Reactions · Types of Oxidation-Reduction Reactions · Acid-Base Reactions · Identifying Reaction Types: Summary

Slide 4 / 142 Chemical Equations Return to Table of Contents Slide 5 / 142 Chemical Equations Chemical equations are concise representations of chemical reactions. + --> + ⇒ CH 4 (g) + 2O 2 (g) --> CO 2 (g) + 2H 2 O(g) Slide 6 / 142 Chemical Equations The formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right). To write a word equation, write the names of the reactants to the left of the arrow separated by plus signs. Write the names of the products to the right of the arrow, also separated by plus signs. Reactant + Reactant Product + Product

Slide 7 / 142 Symbols used in chemical equations Slide 8 / 142 Skeleton equations A skeleton equation is a chemical equation that does not indicate the relative amounts of the reactants and products. Write the formulas of the reactants to the left of the yields sign (arrow) and the formulas of the products to the right. Here is the equation for rusting: Metallic Iron reacts with oxygen in the air to produce iron (III) oxide (rust). Iron ( metal) + Oxygen ( gas) ⇒ iron (III) oxide ( solid) (word equation) Fe + O 2 # Fe 2 O 3 ( skeleton /chemical equation) Slide 9 / 142 Word Equations When ignited, methane gas reacts with oxygen gas to produce carbon dioxide and steam. + ⇒ + CH 4 gas CO 2 gas O 2 gas H 2 O gas This "skeleton" equation is not balanced: CH 4 ( g ) + O 2 ( g ) H 2 O ( g ) + CO 2 ( g )

Slide 10 / 142 1 In the reaction CH 4 ( g ) + O 2 ( g ) # H 2 O ( g ) + CO 2 ( g ) the products are: A oxygen and water B carbon dioxide and water C oxygen and methane D methane and carbon dioxide E I don't know the answer to this. answer Slide 11 / 142 2 In the reaction CH 4 ( g ) + O 2 ( g ) # H 2 O ( g ) + CO 2 ( g ) the products are: A solids B liquids C gases D dissolved in water (aqueous) E cannot be determined answer F I don't know how to answer this. Slide 12 / 142 Word equations to Chemical equations Solid potasium chlorate decomposes in air to produce solid potassium chloride and oxygen gas. The word equation is: potasium chlorate (s) --> potassium chloride (s) + oxygen (g) The unbalanced "skeleton" equation is: KClO 3(s) KCl (s) + O 2(g)

Slide 13 / 142 Word equations to Chemical equations Write the word equation, then the skeleton equation Aluminum sulfate reacts with calcium chloride to produce calcium sulfate and aluminum chloride Aluminum sulfate + calcium chloride --> calcium sulfate + aluminum chloride Slide for Word equation Slide for Skeleton equation Al 2 (SO 4 ) 3 + CaCl 2 --> Ca(SO 4 ) + AlCl 3 Slide 14 / 142 Law of Conservation of Mass “We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal amount of matter exists both before and after the experiment. Upon this principle, the whole art of performing chemical experiments depends.” --Antoine Lavoisier, 1789 Slide 15 / 142 Balancing Equations Return to Table of Contents

Slide 16 / 142 Balancing chemical equations To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass. This is a balanced equation for making a bicycle. The numbers are called coefficients—small whole numbers that are placed in front of the formulas in an equation in order to balance it. Slide 17 / 142 Balancing chemical equations CH 4 ( g ) + 2 O 2 ( g ) # CO 2 ( g ) + 2 H 2 O ( g ) 2 O 1C 1C 4 O 4H 4H 2 O Products appear on the Reactants appear on the right side of the equation. left side of the equation. The states of the reactants and products are written in parentheses to the right of each compound. Slide 18 / 142 Balancing chemical equations CH 4 ( g ) + 2 O 2 ( g ) # CO 2 ( g ) + 2 H 2 O ( g ) 2 O 1C 1C 4 O 4H 4H 2 O Coefficients are inserted to balance the equation.

Slide 19 / 142 Subscripts and Coefficients Subscripts tell the number of atoms of each element in a molecule. Coefficients tell the number of representative particles (atoms, molecules, or formula units). Slide 20 / 142 3 How many oxygen atoms are in one formula unit of calcium nitrate? (First, write the formula for calcium nitrate.) A 2 B 3 answer C 5 D 6 E I don't know how to answer this. Slide 21 / 142 4 How many nitrogen atoms are in one formula unit of ammonium sulfate? answer

Slide 22 / 142 Slide 23 / 142 Balancing chemical equations Write a balanced chemical equation for this reaction. First write a skeleton equation chlorine + sodium bromide # bromine + sodium chloride Cl 2 + NaBr # # Br 2 + NaCl Slide 24 / 142 Balancing chemical equations Then, count up the number of each type of element on each side of the reaction Cl 2 + NaBr # # Br 2 + NaCl Reactants Products Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2

Slide 25 / 142 Balancing chemical equations Next, identify one element that is not balanced. It is best to start with an easy element. The fewer places an element appears on both sides of a reaction, the easier it will be to balance. Cl 2 + NaBr # # Br 2 + NaCl Reactants Products Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2 Slide 26 / 142 Balancing chemical equations Identify the side that needs more of that particular element. Cl 2 + NaBr # # Br 2 + NaCl Reactants Products Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2 Slide 27 / 142 Balancing chemical equations Determine which molecule or element will be getting the coefficient. In this case, because we need more chlorine on the products side, we will have to add a coefficent to the NaCl, since that is the only product containing chlorine. Cl 2 + NaBr # # Br 2 + NaCl Reactants Products Cl: 2 Cl: 2 Cl: 1 Na: 1 Na: 1 Na: 1 Br: 1 Br: 1 Br: 2

Slide 28 / 142 Balancing chemical equations To figure out what the coefficient should be, simply take the amount of that specific element you need from the molecule, and divide by the amount of the element you have in the molecule. Cl 2 + NaBr # # Br 2 + __NaCl 2 Reactants Products Cl: 2 Need Have = 2 1 = Cl: 2 Cl: 1 Na: 1 Na: 1 Na: 1 Br: 1 2 Br: 1 Br: 2 If this is not a whole number, simply multiply ALL the substances in the reaction by some whole number to make the coefficients whole numbers. Slide 29 / 142 Balancing chemical equations Now, just reevaluate the amount of each element on the table Cl 2 + NaBr # # Br 2 + 2NaCl Reactants Products Cl: 2 Cl: 2 Cl: 1 2 Na: 1 Na: 1 Na: 1 2 Br: 1 Br: 1 Br: 2 Slide 30 / 142 Balancing chemical equations Continue with these steps until all the elements are balanced. When all the elements exist in equal amounts on both sides of the equation, you have a balanced chemical equation. Cl 2 + 2NaBr # # Br 2 + 2NaCl Reactants Products Cl: 2 Cl: 2 Cl: 1 2 Na: 1 Na: 1 2 Na: 1 2 Br: 1 Br: 1 2 Br: 2

Slide 31 / 142 Balancing chemical equations SPECIAL NOTE: Make sure that when you are calculating your coefficents you are only looking at the amounts needed/had by individual elements or molecules CH 3 OH + O 2 # # CO 2 + 2H 2 O Reactants Products Cl: 2 C: 1 C: 1 Na: 1 H: 4 H: 2 4 Br: 1 O: 1+2=3 O: 2+1=3 2+2=4 Slide 32 / 142 Balancing chemical equations SPECIAL NOTE: Here is the incorrect way to evaluate the coefficent in this case CH 3 OH + O 2 # # CO 2 + 2H 2 O Reactants Products Cl: 2 C: 1 C: 1 Na: 1 H: 4 H: 2 4 Br: 1 O: 1+2=3 O: 2+1=3 2+2=4 Have = 4 Need 3 = WRONG!!! Slide 33 / 142 Balancing chemical equations SPECIAL NOTE: Here is the correct way to evaluate the coefficent in this case CH 3 OH + O 2 # # CO 2 + 2H 2 O Reactants Products Cl: 2 C: 1 C: 1 Na: 1 H: 4 H: 2 4 Br: 1 O: 1+2=3 O: 2+1=3 2+2=4 Because we already have 1 Oxygen from CH 3 OH, we only need 3 Oxygen Have = 4 - 1 Need from O 2 3 = 2 2 Because O 2 only has 2 Oxygen, the denominator must be 2.

Slide 34 / 142 Balancing chemical equations SPECIAL NOTE: Remember to make sure you get rid of ALL fractions. 3 2CH 3 OH + 2x O 2 # # 2 CO 2 + 2x2H 2 O 2 Reactants Products Cl: 2 C: 1 2 C: 1 2 Na: 1 H: 4 8 H: 2 4 8 Br: 1 O: 1+2=3 2+6=8 O: 2+1=3 2+2=4 4+4=8 Slide 35 / 142 Balancing chemical equations If you follow these steps, you'll be able to balance any type of reaction. 2CH 3 OH + 3O 2 # # 2 CO 2 + 4H 2 O Reactants Products Cl: 2 C: 1 2 C: 1 2 Na: 1 H: 4 8 H: 2 4 8 Br: 1 O: 1+2=3 2+6=8 O: 2+1=3 2+2=4 4+4=8 Slide 36 / 142 5 When the following equation is balanced, the coefficients are: Na + O 2 # Na 2 O A 1, 1, 1 B 1, 2, 4 C 4, 1, 2 D 2, 2, 1 answer E 4, 1, 4