Chemical Reactions

Types of Reactions There are five types of chemical reactions we will talk about: Synthesis reactions Decomposition reactions Single displacement reactions Double replacement reactions Combustion reactions You need to be able to identify the type of reaction and predict the products

Steps to Writing Reactions Some steps for doing reactions Identify the type of reaction Predict the products using the type of reaction as a model Balance the equation Don’t forget about the diatomic elements! 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 (generally elements) combine and form a compound. reactant + reactant  1 product Basically: A + B  AB Example: 2H 2 + O 2  2H 2 O Example: C + O 2  CO 2 The key to recognizing a synthesis reaction is to look for only one product!

Synthesis Reactions

Practice Predict the products. Write and balance the following synthesis reaction equations. Sodium metal reacts with chlorine gas Magnesium reacts with fluorine gas Aluminum reacts with oxygen gas

2. Decomposition Reactions Decomposition reactions occur when a compound breaks up into the elements or to simpler compounds 1 Reactant  Product + Product In general: AB  A + B Example: 2 H 2 O  2H 2 + O 2 The key to recognizing decomposition reactions is to look for only one reactant.

Decomposition Reactions

Practice Predict the products. Then, write and balance the following decomposition reaction equations: Solid Lead (IV) oxide decomposes Solid Aluminum nitride decomposes Iron (III) chloride decomposes

Practice Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation: Nitrogen and oxygen react to form nitrogen monoxide. Solid cobalt reacts with solid sulfur to form cobalt (III)sulfide. Solid nitrogen triiodide decomposes.

Single replacement reactions She’s seeing another man!

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  new element + new compound A + BC  AC + B (if A is a metal) OR A + BC  BA + C (if A is a nonmetal) Key to recognizing single replacement reactions: Look for a pure element on each side of the equation. K + H 2 0  KOH + H 2

Single Replacement Reactions

Write and balance the following single replacement reaction equations: Zinc metal reacts with aqueous hydrochloric acid (HCl) Bromine gas reacts with sodium iodide. Silver reacts with aqueous potassium nitrate.

Single Replacement Reactions More practice Sodium chloride solid reacts with fluorine gas Aluminum metal reacts with aqueous copper (II) nitrate

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  new compound + new compound AB + CD  AD + CB

Double replacement reactions: Examples AgNO 3 + NaCl  AgCl + NaNO 3 K 2 SO 4 + Ba(NO 3 ) 2  KNO 3 + BaSO 4 The ions switch partners, like in square dancing.

Practice Predict the products. Balance the equation. HCl (aq) + AgNO 3(aq)  CaCl 2(aq) + Na 3 PO 4(aq)  Pb(NO 3 ) 2(aq) + BaCl 2(aq)  FeCl 3(aq) + NaOH (aq)  H 2 SO 4(aq) + NaOH (aq) 

5. Combustion Reactions Combustion reactions occur when a substance 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 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)

Combustion Reactions In general: C x H y + O 2  CO 2 + H 2 O Products in combustion of hydrocarbons 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 C 8 H 18 )

Combustion Example C 5 H 12 + O 2  CO 2 + H 2 O Write the products and balance the following combustion reaction: C 10 H 22 + O 2  5 6 8

Mixed Practice State the type, predict the products, and balance the following reactions: BaCl 2 + H 2 SO 4  C 6 H 12 + O 2  Zn + CuSO 4  Cs + Br 2  FeCO 3 

Redox Reactions. Oxidation Reduction

GCSE Oxidation: Gain of oxygen Loss of electrons Reduction: Loss of oxygen Gain of electrons Increase in oxidation number Decrease in oxidation number

4 Experiments: 1. Burning magnesium 2. Copper in silver nitrate solution 3. Chlorine solution and potassium iodide solution 4. Sodium in Water Word equation Balanced symbol equation

2Mg(s) + O 2 (g)  2MgO(s) Oxidised – gains oxygen Must be a redox! Mg  Mg 2+ O  O 2- Put the e - in. +2e - Oxidised – loss of e - Reduced – gain of e -

Cu(s) + 2AgNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2Ag(s) Ag +  Ag Ag +  Ag Cu  Cu 2+ Complete the half- equations +e - +2e - Oxidised? Reduced? Oxidised – loss of e - Reduced – gain of e -

H 2 (g) + ½ O 2 (g)  H 2 O(g) Covalent! No H + or OH - Need a new definition.

GCSE Oxidation: Gain of oxygen Loss of electrons Reduction: Loss of oxygen Gain of electrons Increase in oxidation number Decrease in oxidation number

Redox Reactions. Oxidation Reduction

Oxidation Numbers The oxidation number of an atom in an element is zero. E.g. Mg in Mg, O in O 2. The oxidation number of an atom in an element is zero. E.g. Mg in Mg, O in O 2.

Oxidation Numbers The oxidation numbers of atoms in a compound add up to zero. The oxidation numbers of atoms in a compound add up to zero. F O-2 H+1 Cl Oxidation state of C in CO 2 ? ? – 4 = 0 ? = +4 Put the +!

Oxidation Numbers The oxidation numbers of atoms in a compound add up to zero. The oxidation numbers of atoms in a compound add up to zero. F O-2 H+1 Cl Oxidation state of Mg in MgCl 2 ? +2

Oxidation Numbers The oxidation numbers of atoms in a compound add up to zero. The oxidation numbers of atoms in a compound add up to zero. F O-2 H+1 Cl Oxidation state of N in NH 3 ? -3

Oxidation Numbers The oxidation numbers of atoms in an ion add up to the charge on the ion. The oxidation numbers of atoms in an ion add up to the charge on the ion. F O-2 H+1 Cl Oxidation state of S in SO 4 2- ? ? – 8 = -2 ? = +6

Oxidation Numbers The oxidation numbers of atoms in an ion add up to the charge on the ion. The oxidation numbers of atoms in an ion add up to the charge on the ion. F O-2 H+1 Cl Oxidation state of S in S 2- ? -2

Oxidation Numbers The oxidation numbers of atoms in an ion add up to the charge on the ion. The oxidation numbers of atoms in an ion add up to the charge on the ion. F O-2 H+1 Cl Oxidation state of N in NH 4 + ? -3

H 2 (g) + ½ O 2 (g)  H 2 O(g) Covalent! No H + or OH - Need a new definition.

GCSE Oxidation: Gain of oxygen Loss of electrons Reduction: Loss of oxygen Gain of electrons Increase in oxidation number Decrease in oxidation number

H 2 (g) + ½ O 2 (g)  H 2 O(g) Covalent! No H + or OH - Need a new definition O H

H 2 (g) + ½ O 2 (g)  H 2 O(g) O H Oxidised? H – increase in oxidation number Reduced? O – decrease in oxidation number