Redox
Definition: reactions which both oxidation and reduction reactions take place at the same time.
Oxidation
Gain in oxygen
Lose of electrons
Lose of hydrogen
Increase in oxidation state number
Reduction
Lose of oxygen
Gain of electrons
Gain in hydrogen
Decrease in oxidation state number
Fixed Oxidation numbers
0
All elements, noble gases, metals
+1
Group 1 ions, H+
+2
Group 2 ions
+3
Al3+
-1
Group 7 ions, Oxygen in H2O2, hydrogen in Metal hydrides e.g NaH
-2
O2-, S2-.
-3
Nitrides N3-
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Entry by
Json Lim
http://www.oleveltuition.com/
Wednesday, September 30, 2009
Rate of Reaction
Rate of reactions
Rate of reaction can be calculated and compare by measuring a loss of mass or amount of gas collected.
Factors affected rate of reaction
• Particle size
• Temperature
• Pressure (only for all gas system)
• Catalyst
• Concentration
Use this standard statement to answer your question.
Increase in temperature leads to an increase in the energy of the particles which leads to an increase in number of collisions. This leads to an increase in number of effective collisions which leads to an increase in rate of reaction. The Itallic and bold words can be change to accommodate the factors.
e.g. Increase in particle sizes leads to an increase in the surface area of the reagent which leads to an increase in number of collisions. This leads to an increase in rate of reaction which leads to an increase in rate of reaction. GOT IT? When plotting graphs, the number of moles of products determine the end point of the reaction!
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Rate of reaction can be calculated and compare by measuring a loss of mass or amount of gas collected.
Factors affected rate of reaction
• Particle size
• Temperature
• Pressure (only for all gas system)
• Catalyst
• Concentration
Use this standard statement to answer your question.
Increase in temperature leads to an increase in the energy of the particles which leads to an increase in number of collisions. This leads to an increase in number of effective collisions which leads to an increase in rate of reaction. The Itallic and bold words can be change to accommodate the factors.
e.g. Increase in particle sizes leads to an increase in the surface area of the reagent which leads to an increase in number of collisions. This leads to an increase in rate of reaction which leads to an increase in rate of reaction. GOT IT? When plotting graphs, the number of moles of products determine the end point of the reaction!
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Energy Changes
Energy Changes
Enthalpy change is the amount of heat released or absorbed when a chemical reaction occurs.
Exothermic reaction – liberates heat energy to the surroundings which results in a general increase in the temperature of the surroundings.
Endothermic reaction – absorbs heat energy to the surroundings which results in a general decrease in the temperature of the surroundings.
Type of reactions Enthalpy Product energy level
Exothermic
ΔH= - ve because more heat is given out during bond forming than heat taken in to break them
Product is at a lower energy compared to reagent.
Bonds of products are stronger than bonds in reagent.
Endothermic
ΔH=+ ve because more heat is taken in to break bonds than heat is given out when bonds form.
Product is at a higher energy compared to reagent.
Bonds of reactants are stronger than products.
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
Enthalpy change is the amount of heat released or absorbed when a chemical reaction occurs.
Exothermic reaction – liberates heat energy to the surroundings which results in a general increase in the temperature of the surroundings.
Endothermic reaction – absorbs heat energy to the surroundings which results in a general decrease in the temperature of the surroundings.
Type of reactions Enthalpy Product energy level
Exothermic
ΔH= - ve because more heat is given out during bond forming than heat taken in to break them
Product is at a lower energy compared to reagent.
Bonds of products are stronger than bonds in reagent.
Endothermic
ΔH=+ ve because more heat is taken in to break bonds than heat is given out when bonds form.
Product is at a higher energy compared to reagent.
Bonds of reactants are stronger than products.
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Entry by
Json Lim
http://www.oleveltuition.com/
Electrolytes
5 types of electrolysis systems
• Molten salt – the 2 ions will discharge
• Aqueous salt – hydrogen (unless metal is below hydrogen in that case the metal will discharge) and hydroxide ions (ALWAYS) will discharge
• Acidic solution - hydrogen and hydroxide ions will discharge
• Concentrated chlorides solution – ALWAYS chloride ions, positive ions the usual method of looking at reactivity series of methods for discharge order.
• Reactive anode (used in the purification of copper or electroplating) – anode dissolves into the solution. UNDER NO CIRCUMSTANCES will cathode dissolve. Even in simple cells the plate that dissolve (i.e. the more reactive plate that dissolves in the anode).
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Json Lim
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• Molten salt – the 2 ions will discharge
• Aqueous salt – hydrogen (unless metal is below hydrogen in that case the metal will discharge) and hydroxide ions (ALWAYS) will discharge
• Acidic solution - hydrogen and hydroxide ions will discharge
• Concentrated chlorides solution – ALWAYS chloride ions, positive ions the usual method of looking at reactivity series of methods for discharge order.
• Reactive anode (used in the purification of copper or electroplating) – anode dissolves into the solution. UNDER NO CIRCUMSTANCES will cathode dissolve. Even in simple cells the plate that dissolve (i.e. the more reactive plate that dissolves in the anode).
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Entry by
Json Lim
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Intermolecular Forces and Intramolecular forces for Graphite
Note for graphite, both covalent and intermolecular force of attraction applies. (Pure)
When explaining the high temperature in which graphite melts, we say that they are breaking strong covalent bonds. (Pure)
When explaining why graphite act like a lubricant, we say that the graphite molecules are arranged in layers which are held by weak IMF therefore can slide over each other easily. GET IT? (Pure)
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Json Lim
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When explaining the high temperature in which graphite melts, we say that they are breaking strong covalent bonds. (Pure)
When explaining why graphite act like a lubricant, we say that the graphite molecules are arranged in layers which are held by weak IMF therefore can slide over each other easily. GET IT? (Pure)
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Json Lim
http://www.oleveltuition.com/
Bonding
Bonding and Structures
Chemical bond is a force of attraction holding atoms together in a molecule or crystal
Three types of chemical bonds
• Ionic bonding
• Covalent bonding
• Metallic bonding
Ionic bonding – involving metal and non-metal elements. Force of attraction between oppositely charged ions. Only exception is compounds like ammonium salts. Although ammonium is made up entirely of NON_METAL, it is still an Ionic compound because it contains charges.
Covalent bond – formed between 2 combining atoms of non-metallic by mutual sharing of one or more electrons
Metallic bonding – type of chemical bond that holds the atoms together in a solid metal. It’s the attraction between the sea of electrons and the positive metal ions. (more important for pure chem.)
Covalent compounds
- simple molecular compounds like hydrogen molecule, water molecule etc.
- giant molecular structure like diamonds and silicon dioxide (pure)
- graphite
Ionic compounds – self explanatory
Metallic substances – pure metals and alloys
Types of substances
Simple molecular
Types of bonds broken during change of state: Intermolecular forces of attraction.
Strength of the bond broken:Weak
Melting point and Boiling point:Low
Giant molecular or Giant Covalent
Types of bonds broken during change of state:Covalent
Strength of the bond broken:Strong
Melting point and Boiling point:High
Ionic Compounds
Types of bonds broken during change of state:Ionic Bonds
Strength of the bond broken:Strong
Melting point and Boiling point:High
Metals Types of bonds broken during change of state:Metallic Bonds
Strength of the bond broken:Strong
Melting point and Boiling point:High
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Entry by
Json Lim
http://www.oleveltuition.com/
Chemical bond is a force of attraction holding atoms together in a molecule or crystal
Three types of chemical bonds
• Ionic bonding
• Covalent bonding
• Metallic bonding
Ionic bonding – involving metal and non-metal elements. Force of attraction between oppositely charged ions. Only exception is compounds like ammonium salts. Although ammonium is made up entirely of NON_METAL, it is still an Ionic compound because it contains charges.
Covalent bond – formed between 2 combining atoms of non-metallic by mutual sharing of one or more electrons
Metallic bonding – type of chemical bond that holds the atoms together in a solid metal. It’s the attraction between the sea of electrons and the positive metal ions. (more important for pure chem.)
Covalent compounds
- simple molecular compounds like hydrogen molecule, water molecule etc.
- giant molecular structure like diamonds and silicon dioxide (pure)
- graphite
Ionic compounds – self explanatory
Metallic substances – pure metals and alloys
Types of substances
Simple molecular
Types of bonds broken during change of state: Intermolecular forces of attraction.
Strength of the bond broken:Weak
Melting point and Boiling point:Low
Giant molecular or Giant Covalent
Types of bonds broken during change of state:Covalent
Strength of the bond broken:Strong
Melting point and Boiling point:High
Ionic Compounds
Types of bonds broken during change of state:Ionic Bonds
Strength of the bond broken:Strong
Melting point and Boiling point:High
Metals Types of bonds broken during change of state:Metallic Bonds
Strength of the bond broken:Strong
Melting point and Boiling point:High
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Entry by
Json Lim
http://www.oleveltuition.com/
Atomic Structure Again
Atomic Structure
Particle
Proton
Relative mass 1
Relative Charge +1
Neutron
Relative mass 1
Relative Charge 0
Electron
Relative mass 1/2000 or appro = 0 or 1/1840
Relative Charge -1
Proton number = Number of protons or neutrons in an atom
Nucleon number = sum of number of neutrons and protons in an atom. (Note this is not the same as relative atomic mass although in our syllabus it is the same for most atoms)
Isotopes are atoms of the same element having the same atomic number but different number of neutrons
Remember anything more than proton number 20, you CANNOT draw the electronic configuration. If the questions or number of valence electrons, LOOK AT GROUP NUMBER!!
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Entry by
Json Lim
http://www.oleveltuition.com/
Particle
Proton
Relative mass 1
Relative Charge +1
Neutron
Relative mass 1
Relative Charge 0
Electron
Relative mass 1/2000 or appro = 0 or 1/1840
Relative Charge -1
Proton number = Number of protons or neutrons in an atom
Nucleon number = sum of number of neutrons and protons in an atom. (Note this is not the same as relative atomic mass although in our syllabus it is the same for most atoms)
Isotopes are atoms of the same element having the same atomic number but different number of neutrons
Remember anything more than proton number 20, you CANNOT draw the electronic configuration. If the questions or number of valence electrons, LOOK AT GROUP NUMBER!!
Enjoy!
Entry by
Json Lim
http://www.oleveltuition.com/
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