Chemical Reactions

Chemical Reactions Chapter 11

Products “ ” means “yields” or “reacts to produce.” Using Everyday Equations A chemical reaction involves one or more substances, the reactants, changing into one or more substances, the products. Reactants

Fe2O3 Example: Fe + O2 (Skeleton equation) - does not indicate the relative amounts of reactants and products • Most often symbols are used to describe the state (i.e., gas, solid, etc.) of each substance • Gas (aq) Aqueous • Solid • Liquid

Practice __ H2 + ___ O2  ___ H2O __ SO2 + ___ O2  ___ SO3

Try to balance this reaction: 2 3 6 __Al(OH)3(s) + __H2SO4(aq)  __Al2(SO4)3(aq) + __H2O(l) Al S H O 2 3 2 13 Al S H O 1 1 5 7 2 3 12 8 12 10 18 18

Balance these equations • __ Mg + __ O2 → __ MgO • __ KClO3 → __ KCl + __ O2 • __ Cu + __ AgNO3→ __ Cu(NO3)2 + __ Ag • __KOH + __ H3PO4 → __ K3PO4 + __ H2O • 2 Mg + O2 → 2 MgO • 2 KClO3 → 2 KCl + 3 O2 • Cu + 2 AgNO3→ Cu(NO3)2 + 2 Ag • 3 KOH + H3PO4 → K3PO4 + 3 H2O • Even better… • 2 Mg (s) + O2 (g)→ 2 MgO (s)

Start Notes Here 10/29 • Before you start taking notes, take out your reference sheet and go to page 6. • Notice how the information is neatly placed inside your reference sheet??? • Page 7 has the activity series of metals you will need to look at in order to understand single replacement.

Steps to Writing Reactions • Some steps for doing reactions • Identify the type of reaction • Predict the product(s) using the type of reaction as a model • Balance it Don’t forget about the 7 diatomic elements! (BrINClHOF) For example, Oxygen is O2 as anelement. In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!

1. Synthesis reactions • Synthesis reactions occur when two substances (generallyelements) combine and form a compound. (Sometimes these are called combination or addition reactions.) reactant + reactant  1 product • Basically: A + B  AB • Example: 2H2 + O2  2H2O • Example: C+ O2  CO2

2. Decomposition Reactions • Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds • 1 Reactant  Product + Product • In general: AB  A + B • Example: 2 H2O  2H2 + O2 • Example: 2 HgO  2Hg + O2

3. Single Replacement Reactions • Single Replacement Reactions occur when one element replaces another in a compound. • A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). • element + compound product + product A + BC  AC + B (if A is a metal)OR A + BC  BA + C (if A is a nonmetal) (remember the cation always goes first!) When H2O splits into ions, it splits into H+ and OH- (not H+ and O-2 !!)

No, Ni is below Na Yes, Li is above Zn Yes, Al is above Cu Yes, Fe is above Cu We have looked at several reactions: Fe + CuSO4  Cu + Fe2(SO4)3 Li + H2O  LiOH + H2 Such experiments reveal trends. The activity series ranks the relative reactivity of metals. It allows us to predict if certain chemicals will undergo single displacement reactions when mixed: metals near the top are most reactive and will displacing metals near the bottom. Q: Which of these will react? Fe + CuSO4  Ni + NaCl  Li + ZnCO3  Al + CuCl2  Cu + Fe2(SO4)3 NR (no reaction) Zn + Li2CO3 Cu + AlCl3

cold H2O H is the only nonmetal listed. H2 may be displaced from acids or can be given off when a metal reacts with H2O (producing H2 + metal hydroxide). The reaction with H2O depends on metal reactivity & water temp. Q: will Mg react with H2O? hot H2O steam A: No for cold, yes if it is hot/steam Mg + H2O  H2 + Mg(OH)2 acid Q: Zn + HCl  H2 + ZnCl2 Complete these reactions: Al + H2O(steam)  Cu + H2O  Ca + H2SO4  Na + H2O  H2 + Al(OH)3 NR H2 + CaSO4 H2 + NaOH

Other Activity Series Information • All metals will have a specific place in the activity series. For simplicity, only the most common metals are shown. • The metals near the top of the activity series are more reactive because their valence electrons are more easily removed. • On tests and exams the activity series may appear as K, Na, … Ag, Au; you must remember that K is reactive, Au is not. • If the valence of a metal is not indicated in the question, use its most common valence (in bold on your periodic table) to determine the correct chemical formula.

Single Replacement Reactions • Write and balance the following single replacement reaction equation: • Zinc metal reacts with aqueous hydrochloric acid Zn(s) + HCl(aq) ZnCl2 + H2(g) Note: Zinc replaces the hydrogen ion in the reaction 2

4. Double Replacement Reactions • Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound • Compound + compound  product + product • AB + CD  AD + CB

Double Replacement Reactions • Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together • Example: AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq) • Another example: K2SO4(aq) + Ba(NO3)2(aq)  KNO3(aq) + BaSO4(s) 2

5. Combustion Reactions • Combustion reactions occur when a hydrocarbon reacts with oxygen gas. • This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”:1) A Fuel (hydrocarbon)2) Oxygen to burn it with3) Something to ignite the reaction (spark)

Combustion Reactions • In general: CxHy + O2  CO2 + H2O • Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide) • Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)

Combustion • Example • C5H12 + O2 CO2 + H2O • Write the products and balance the following combustion reaction: • C10H22 + O2  8 5 6

Chemical Reactions