Chemical Reactions Unit 11 (Chapter 11)

Chemical Reactions A chemical reaction is a chemical change Changes the way atoms are bonded to each other Chemical reactions are described by chemical equations Two types: Word Equations Chemical Equations

Word Equations Uses the names of the chemicals Reactants  Products “Reactants YIELD Products” Can have multiple of both, separated by a plus sign that means “and” Ex) Potassium iodide + hydrogen peroxide  Iodine + water + oxygen

Chemical Equations The most common way to show chemical reactions Shows the chemical formulas as symbols Still has the reactants on the left, and products on the right P + P  R + R A “skeleton equation” is a chemical equation that doesn’t tell you how many of each reactant or product you have

Let’s all try making a skeleton equation You are reacting pure iron and chlorine gas (Cl2) to make iron (III) chloride. Write the skeleton equation.

Try these. Write the skeleton equation for reacting nitrogen gas (N2) with oxygen gas (O2) to form nitrogen dioxide (NO2). Write the skeleton reaction that results when propane (C3H8) reacts with oxygen gas to form carbon dioxide and water.

Catalysts Catalysts are a chemical that “helps” the reaction happen, but doesn’t actually react or get changed. In a chemical equation, the catalyst is written on top of the arrow

Write another skeleton reaction Write a reaction where water is broken down to form hydrogen gas (H2) and oxygen gas (O2). Sodium hydroxide is the catalyst.

Symbols we’ll use +  (s) (l) (g) (aq) “and” between two products or reactants  Yields Reversible reaction (s) A solid (l) A liquid (g) A gas (aq) “Aqueous” solution (dissolved in water) Uses heat to do the reaction. Uses a catalyst (in this case, an iodide ion) Symbols we’ll use heat or Δ I-

Okay, one more practice skeleton equation Liquid acetone (C3H6O) reacts with oxygen gas to form liquid water and carbon dioxide gas.

Balancing Chemical Equations Skeleton equations just tell you WHAT chemicals are in a chemical reaction Ex) H2O2  H2O + O2 But it is also important to know HOW MANY there are A “balanced” chemical equation tells you what chemicals and how many there are in a chemical reaction. The number of each chemical is called the “coefficient” and is put IN FRONT of the symbols Ex) 2 H2O2  2 H2O + O2

Let’s take a set back… If I tell you to make a bookshelf, what do you need? What if you want to make a bookshelf and an end table?

Let’s take a set back… 5 shelves + 2 sides + 1back  1 bookshelf. 7 shelves + 2 sides + 1 drawer + 4 legs  1 bookshelf and 1 end table

How to balance equations Remember the Law of Conservation of Matter? Matter is not created or destroyed So, there MUST be the EXACT SAME number of each element in the reactants as the products! Use coefficients to make the number of elements equal on both sides. Basically a balancing “game”.

Let’s try one or two Balance these reactions: Fe + O2  Fe2O3 CaS + H2O  Ca(OH)2 + H2S

Some “rules” and tips to help you balance Start with 1 element in the reactants, and balance it with the number in the products. Choose elements that are in only 1 of the products first, just to make it easier. Then balance the one that is bonded to the first element in the reactant. Then balance the one that is attached to that one (if there is one). Polyatomic ions usually stay together, so can be treated like a single element, rather than more than 1. Check to see if it stays together first.

Try this… React aluminum metal with oxygen to form aluminum oxide. Barium chloride (aq) reacts with potassium sulfate (aq) reacts to form barium sulfate (s) plus potassium chloride (aq)

Balancing equations worksheet General notes on the back, just to help. Depends on what you mean by “help”, I guess.

The 5 Types of Chemical Reactions! To put together Combination (or Synthesis) Breaking apart Decomposition One swap places with another Single replacement Two swap partners Double Replacement To break apart C-H with O2 Combustion The 5 Types of Chemical Reactions!

http://www.youtube.com/watch?v=tE4668aarck

Combination (Synthesis) Reaction Do not look directly at the flame! 2Mg + O2  2 MgO

Decomposition Reaction https://www.youtube.com/watch?v=ritaljhhk7s 2Hg(SCN)2 → 2HgS + CS2 + C3N4

Single Replacement https://www.youtube.com/watch?v=OxGjbHzxQSI Fe + 2CuCl  2Cu + FeCl2

Double Replacement Reactions https://www.youtube.com/watch?v=opY3FLrPTa4 K2CrO4 + 2AgNO3  Ag2CrO4 + 2KNO 2KI + Pb(NO3)2 = PbI2 + 2KNO3

Combustion Reaction WHAT?!? 2 C3H6O + 9 O2  6 CO2 + 6 H2O

Predicting Products of Chemical Reactions. Combination Just combine the two element, balance charges if ionic. Decomposition Split the elements, make diatomic of HONClBrF Single replacement The pure element will replace one of the other elements, with a pure element (or ion) being alone. Double replacement The four elements (or ions) will switch places, with the charges balanced out. Combustion End with H2O and CO2 (sometimes CO) CO2 will be equal to the C’s in reactants.

Let’s try these reactions… Decomposition: FeCl2  Double replacement: NaOH + H2SO4  Single replacement FeCl3 + Zn 

How about these? Synthesis Ca + O2  Combustion  C4H10 + O2 

Reactions in Aqueous Solutions Aqueous means “in water” Ions usually dissolve in water because ions are charged, and water is also slightly charged (polar) The ions “separate” from each other We can write the ions out as a “complete ionic equation” by showing them separated with their charge and how many you need. Ex) BaCl2 (aq) + K2SO4 (aq)  BaSO4(s) + 2KCl (aq) could be re-written as: Ba2+(aq) + 2 Cl-(aq) + 2 K+(aq) + SO42+(aq)  BaSO42+(s) + 2 K+ (aq) + 2Cl- (aq)

Ba2+(aq) + 2 Cl-(aq) + 2 K+(aq) + SO42+(aq)  BaSO42+(s) + 2 K+ (aq) + 2Cl- (aq) See how the K and Cl don’t really do anything? They just stay as aqueous. We call them “spectator ions”. The shorter way to write a reaction in an aqueous is called a “net ionic equation” by getting rid of the spectator ions. From (original equation): Ba2+(aq) + 2 Cl-(aq) + 2 K+(aq) + SO42+(aq)  BaSO42+(s) + 2 K+ (aq) + 2Cl- (aq) To (net ionic equation): Ba2+(aq) + SO42+(aq)  BaSO42+(s)

Let’s try one: Write the complete ionic equation, spectator ions AND the net ionic equation for the following equation: AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) Complete ionic equation: Spectator ions: Net ionic equation:

How do we know if it becomes solid? Follow the (basic) solubility rules: The following are soluble Salts of alkali metals (or NH4+) are usually soluble Nitrates and chlorates are usually soluble Sulfates except for Lead (II), Silver, Mercury (I), Alkaline Earth Metals (Group 2) except Magnesium Chlorides except Silver, Lead (II), and Mercury (I) The following are USUALLY not soluble: Carbonates, phosphates, chromates, sulfides, and hydroxides (unless it’s alkali metals)

Do you need to memorize that?

So, let’s try one more, for “fun” You are going to react lead (II) chlorate with sodium iodide in an aqueous solution. Write a balanced equation, with states. Which ions would become a solid? Write the complete ionic equation. What are the spectator ions? What is the net ionic equation?