Types of Reactions

Recall A + B  C + D A and B are called reactants Means ‘yields’ C and D are called products

Evidence of chemical reactions At least one of these should be obvious when a chemical reaction takes place: Color change - new substances might reflect different colors of light. Heat change - the container may get hotter or colder. Gas produced - bubbles or smoke may be observed. Precipitate formed - an insoluble solid might form in a liquid.

Types of reactions: Synthesis – to build up Decomposition – to break down Single displacement – to replace one thing Double displacement–to replace two things Combustion – burn in presence of oxygen

Synthesis This reaction involves the combination of smaller atoms and/or molecules to produce a single product. Hydrogen chloride and ammonia yield ammonium chloride HCl + NH3  NH4Cl

Decomposition This reaction involves the splitting of a large molecule into elements or smaller molecules. Sodium iodide  sodium and iodine 2NaI  2Na + I2

Single Displacement This chemical change involves an element and a compound as reactants. One element will DISPLACE the element from the compound. Mg + Ag(NO3)  Ag + Mg(NO3)2

Double Displacement This reaction occurs when elements in different compounds displace each other or exchange places. Pb(NO3)2 + KI  PbI2 + K(NO3)

Acid + Base  salt + water Double Displacement Neutralization of an acid and a base is also an example of a double displacement reaction. Acid + Base  salt + water Ex. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)

Combustion This is generally a very quick reaction where one reactant is oxygen and the product formed is an oxide. Mg + O2  MgO C4H10 + O2  CO2 + H20 (complete combustion) Incomplete combustion forms CO2, CO, C and H2O

Metal oxides Mg + O2  MgO(s) MgO(s) + H2O(l)  Mg(OH)2(aq) pH scale measure the amount of hydrogen ions in the solution. pH scale: 0 (very acidic) 7(neutral) 14 (very basic)

Indicators to measure pH Litmus paper Red litmus turns blue in a base Blue litmus turns red in an acid BTB(bromothymol blue) Turns blue in a base Turns yellow in an acid Turns green in a neutral solution PHTH (phenophthalein) Turns colourless in an acid Turns magenta pink in a base

Non-metal oxide Non-metal oxide and water form an acid. CO2 + H2O(l)  H2CO3(aq) Therefore this would lie under 7 on the pH scale (acidic environment)