chemical reactions sir niamat ullah

Types of chemical reaction Sir Naimat ullah

a process that involves rearrangement of the molecular or ionic structure of a substance, as distinct from a change in physical form or a nuclear reaction.

OR  (Chemistry) a process that involves

changes in the structure and energy content of atoms, molecules, or ions but not their nuclei.

Five Types of Chemical Reactions:

1. Combustion

3. Decomposition

4. Single Displacement

5. Double Displacement

2. Synthesis

Colour / Odour Change

Formation of a gas or solid

Difficult to reverse

Release/Absorption of Energy (heat)

More commonly known as burning

Easily identified (release of heat)

HeatFuel

For combustion 3 things need to be present:

Oxygen

Sulphur (in gasoline):

S(s) + O2(g) SO2(g) + Heat

2 H2(l) + O2(l) 2 H2O(g) + Heat

Rocket Fuel:

Combustion SituationElement in

Reactant

Common

Oxide

Coal in a coal-fired electricity generator carbon CO2 (g)

Burning of rocket fuel Hydrogen H2O (g)

Commercial production of sulphuric acid Sulphur SO2 (g)

Lightning strikes and volcanoes Nitrogren NO2 (g)

combination of two or more simple substances combining to form a more complex substance.

A + B AB

+

22

Synthesis of Magnesium Oxide

C(s) + O2(g) CO2(g)

S(s) + O2(g) SO2(g)

Synthesis Reactions:

Breaking down large, complex molecules or ionic compounds into smaller, simpler entities.

AB A + B

+

Decomposition of Hydrogen PeroxideDecomposition of Hydrogen Peroxide

2 2

reaction of an element with a compound that produces a new element and new compound.

A + BC AC + B

HClHCl(aq)(aq) + Zn + Zn(s) (s) H H2(g)2(g) + ZnCl + ZnCl2(aq)2(aq)2

SOLUTE – is a pure substance (usually lesser in quantity) that is dissolved in another pure substance called the “SOLVENT”

AQUEOUS SOLUTION – a solution in which water is the solvent (aqua – meaning water).

Solutions are homogenous mixtures of solutes and solvents.

Solubility is the measure of how much of the solute can possibly dissolve in a known amount of solvent. If a substance has high solubility in water, it has a subscript of (aq). However, if it isn’t very soluble it will start to precipitate out and will have a (s) subscript for solid.

Is calcium hydroxide soluble? Is sodium flouride soluble? What about lead (II) Iodide?

reaction of two compounds, where the positive and negative ions in their respective compounds switch places to form two new compounds. This can only happen with ionic compounds

AB + CD AD + CB

A double displacement reaction only occurs if one of the following three results are seen:

a precipitate is formed a gas is produced a change of pH occurs (a neutralization reaction)

** If the products are both soluble then the reaction is NR (no reaction)

Pb(NOPb(NO33))2(aq)2(aq) + KI + KI(aq) (aq) PbI PbI2(s)2(s) + KNO + KNO3(aq)3(aq)22

Precipitate: A solid that is formed as a result of the chemical reaction of two aqueous solutions.

FeCl3(aq) + Na2(SO4)2(aq) → ?

NR – both are soluble

HCl(aq) + LiOH(aq) → ?

pH change – neutralization reaction, products are LiCl & H2O

2HNO3(aq)+ K2CO3(aq)→ CO2(g)+H2O(l) + 2 KNO3(aq) gas produced – therefore double displacement

Composition of

Common Alloys

Alloy % Composition Property

Brass Cu (70%)

Zn (30%)

Harder and more resistant to corrosion than copper

Stainless Steel

Fe (80%)

Cr (18%)

Ni (1%)

Si (1%)

More resistant to corrosion then iron

18K gold Au (75%)

Ag (13%)

Cu (12%)

Harder and less malleable than 24K gold

Percentages are calculated by weight

How much gold (in grams) is there in 10g sample of 18K yellow gold where the % composition is 75% Au?

Answer: mass of Au = (75% / 100) x 10g= 7.5 g

Therefore there is 7.5 g of pure gold in a 10g sample of 18K yellow gold.