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Cheatography

Reactions and Stoichiometry Cheat Sheet (DRAFT) by

J1 Chemistry Chapter 4

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Formulae

Relative Isotopic Mass
Mass of 1 atom of an isotope of an element / 1/12 the mass of 1 atom of carbon-12 isotope
Relative Atomic Mass
Avg mass of 1 atom of an element / 1/12 the mass of 1 atom of carbon-12 isotope
Relative Molecu­lar­/Fo­rmula Mass
Avg mass of 1 molecu­le/­formula unit of a substance / 1/12 the mass of 1 atom of carbon-12 isotope
Mr
Sum of Ar of atoms in the molecular formula
Empirical Formula
Simplest formula which shows ratio of atoms of different elements in the compound
Molecular Formula
Formula which shows actual number of atoms of each element in one molecule of the compound
Relative formula mass is used for ionic compounds
Relative masses have no units as they are ratios of 2 masses

Calcul­ations using Volume of Gases

Avogadro's Law:
Equal volume of all gases, under the same temper­ature and pressure, contain the same number of particles (atoms or molecules)

Gases in a balanced equation: Volume ratio = Mole ratio

Molar Volume, Vm:
Volume occupied by 1 mole of the gas at a specific T&P

Standard T&P : 273K (0 degree celsius), 1 bar (100 kPa), 22.7dm­^3/mol
Room T&P: 293K (20 degree celsius), 1 atm (101 kPa), 24 dm^3/mol
Volumes of gases are dependent on T&P hence these conditions must be specified
 

Stoich­iometry

Stoich­iom­etry: Quanti­tative aspects of chemical formulae & reactions

Limiting reactants are completely consumed in the reaction and limit how much products can form.

Percentage Yield =
Actual yield/mass or amount of product formed /
Theore­tical yield/mass or amount of product formed
x 100%

Types of Reactions

Precip­itation Reaction
Reactions which involve formation of insoluble solid (ppt) from reaction of 2 solutions

Types of Reactions

Precip­itation Reaction
Reactions which involve formation of insoluble solid (ppt) from reaction of 2 solutions, Separation by filtration or decanting
Thermal Decomp­osition
Chemical reaction caused by heat, Compounds break down into 2 or more substances
Acid-Base
Elabor­ation in a later segment
Redox
Elabor­ation in a later segment

Calcul­ations using Concen­tra­tions

When a solute is dissolved in a solvent, a solution is formed
If the solvent is water, an aqueous solution is formed

The concen­tration of a solution (mol dm^-3) shows the amt of solute dissolved in a given volume of solution

Standard solution: Solution whose concen­tration is accurately known

[X] - Amt of X (mol) / V of solution (dm^3)

No of moles of solute, n:
- [solute] (mol dm-3) X Volume (dm3)
- Mass of X (g) / Molar mass of X (g/mol)

When a solution is diluted (by adding more solvent), the concen­tration of the solution decreases but no. of moles of solute in the diluted solution remains unchanged
1dm3 = 1000cm3
 

Acid-Base Reactions

Arrhenius Theory of Acids & Bases
- An acid is a substance that dissoc­iates in water to produce H3O+(aq)
- A base is a substance that dissoc­iates in water to produce OH- (aq)
Neutra­lis­ation: H+ (aq) + OH-(aq) -> H2O (l)
Limita­tion: Aqueous solutions only

Bronst­ed-­Lowry Theory of Acids & Bases
- An acid is defined as any species which donates a proton, H+. It must thus contain Hi n its formula
- A base is defined as any species which accepts a proton, H+. It must contain a lone pair of electrons to bind the H+ ions
Bronst­ed-­Lowry acid-base reaction involves the transfer of a proton from an acid to a base. They do no occur only in aq solutions but also between gases and non-aq systems.
Limitation: Does not address why substances such as BF3 or AlCl3 do not contain any H atom but are known to behave as acids

Lewis Theory of Acid & Bases
- An acid is a species that accepts an electron pair, e.g. BF3
- A base is a species that donates an electron pair, e.g. NH3
Lewis acid-base reaction can be viewed as a transfer of a pair of electrons from the base to the acid
Limita­tion: Too general

The 3 models can be used to interpret different acid-base systems
BL and L theories - Describe specific acid-base reactions
Arr theory - Whether isolated substances are acids, bases, or neither
In aqueous solution, H+ does not exist on its own. It forms a dative bond with a water molecule to form H3O+, called hydronium or hydrox­onium ion. Chemists often use H+ and H3O+ interc­han­geably o refer to the elevated H+ ion.

Best to use Bronst­ed-­Lowry theory wherever possible for an acid-base reaction, and apply Lewis theory only when reaction does not involve proton transfer
 

Redox Reactions

Redox Reaction
Reaction that involves reduction and oxidation simult­ane­ously
Reduction
Process whereby a substance gains electrons, resulting in a decrease in OSN
Oxidation
Process whereby a substance loses electrons, resulting in an increase in OSN
Reducing agent (reduc­tant)
Substance that gives electrons to another, itself being oxidised in the process
Oxidising agent (oxidant)
Substance that takes in electrons from another, itself being reduced in the process
Dispro­por­tio­nation
Redox reaction in which the same substance is both oxidised and reduced
Oxidation Number (OSN)
Number of electrons to be added or subtracted from an atom in a combined state to convert it to elemental form
Acronym: OIL RIG
When writing the OSN, +/- signs must be stated before the number

Rules of Assigning OSN

Balancing Redox Reactions

Method 1
1. Balance elements that were oxidised or reduced
2. Balance O with H2O
3. Balance H with H+
4. Balance charges with electrons

Method 2
1. Balance elements that were oxidised or reduced
2. Add electrons (OSN x No of that element)
3. Balance O with H2O
4. Balance H with H+

Method 3
1. Balance elements that were oxidised or reduced
2. Electrons gained = Electrons lost
- a x 7e = b x 2 x 1e
- Same on LHS and RHS, figure out what a and b are, multiply the relevant coeffi­cients
3. Balance O with H2O
4. Balance H with H+

Balancing Redox Reactions

Method 1
1. Balance elements that were oxidised or reduced
2. Balance O with H2O
3. Balance H with H+
4. Balance charges with electrons

Method 2
1. Balance elements that were oxidised or reduced
2. Add electrons (OSN x No of that element)
3. Balance O with H2O
4. Balance H with H+

Method 3
1. Balance elements that were oxidised or reduced
2. Electrons gained = Electrons lost
- a x 7e = b x 2 x 1e
- Same on LHS and RHS, figure out what a and b are, multiply the relevant coeffi­cients
3. Balance O with H2O
4. Balance H with H+