Reactivity and Rates of Reaction

By : Albert Ng

THE MYSTERY OF

SPONTANEOUS COMBUSTION

Learning Objectives How metals react with oxygen How metals react with water How metals react with acids Displacement reactions The reactivity series Measuring rate of reaction by change in mass of the

reactants Measuring rate of reaction by the change in volume of

the product The effect of concentration The effect of particles size The effect of temperature Catalysts

Metal Mostly active Combined readily with non metals such as

oxygen to form stable compounds

Example of Metals: Aluminium Iron Lead Tin Silver Gold Nickel

Sodium Silver-white, highly reactive metal Need to be kept under a layer of oil because it

readily react wit water and oxygen in the air to produce flames

Very soft metal Shiny surface of small cut sodium quickly

tarnished soon it react with air

Comparatively, iron take much longer to react with air ( Rusting of Iron )

INDICATION: Different metals have different speeds at which they react with other chemicals = Different Reactivity

Reaction of metals with oxygen Why most metals lose their lustre over time?

Metals react with oxygen in the air to form metal oxide. This process is called oxidation

Metal + Oxygen Metal Oxide

Example:

Iron + Oxygen Iron Oxide

When metals heated with oxygen A) Copper develop a covering of black powder

without glowing or bursting into flame B) Iron glows and produces yellow sparks, a

black powder is left behind C) Sodium only needs a little heat to make it

burst into yellow flame and burn quickly to leave a white powder behind

D) Gold is not changed after it has been heated and then left to cool

Reaction of metals with water Pg 147

Rocksil wool soaked in

water

Metal Sample

Rubber Bung

Hydrogen

Water

Heat

Calcium A) In COLD water

Sink Form bubble of hydrogen on its surface Bubbles increase over time Water become cloudy as calcium hydroxide

formed

B) Test tube filled with water over fizzing metal

Gas pushes water out of the test tube Tube filled with gas and raised out from water with

a light splint held beneath its mouth Popping sound heard because hydrogen in tube

react with oxygen in the air

Copper Sink in cold water and does not react with it Does not react with steam

Sodium Floats on surface of the water Bubbles of hydrogen produced around it

(Fizzing) Gas produced push the metal across the

surface Metals burst into flame Clear solution of sodium hydroxide formed

VIDEO

Iron Sinks in water No bubbles of hydrogen formed When steamed, hydrogen produced slowly

Magnesium Sinks in water Bubbles of hydrogen produced very slowly Magnesium hydroxide solution formed When heated with steam, hydrogen is

produced quickly

Potassium Floats on water Bursts into flames immediately Hydrogen bubbles rapidly produced around

the metal Clear solution of potassium hydroxide formed

Reaction of metals with acids Pg 149 Piece of metal placed in tube Acid was poured into the tube Bubble of hydrogen gas observed Reactivity of Metals can be compared by comparing the

amount of hydrogen gas produced in the reaction between acid and different metals

Metal+ Hydrochloric Acid Metal Chloride + Hydrogen

Apparatus used in investigating the reaction of some metals (Not sodium or potassium) and hydrochloric

acid

Refer to Page 149

Reaction of metals with dilute HCL and Concentrated HCL

Lead Did not react with dilute HCL Bubbles of hydrogen gas produced slowly

Zinc React slowly with dilute HCL to produce bubbles of

hydrogen

Copper Did not react with either dilute or concentrated HCL

Magnesium React quickly with dilute HCL to produce bubbles of

hydrogen

Reactivity Series