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:

1. Color change - new substances might reflect different colors of light.

2. Heat change - the container may get hotter or colder.

3. Gas produced - bubbles or smoke may be observed.

4. Precipitate formed - an insoluble solid might form in a liquid.

Types of reactions:

1. Synthesis – to build up

2. Decomposition – to break down

3. Single displacement – to replace one thing

4. Double displacement–to replace two things

5. 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)

Double Displacement

• Neutralization of an acid and a base is also an example of a double displacement reaction.

Acid + Base salt + waterEx.

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

1. Mg + O2 MgO(s)

2. 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)