OCR Chemistry A (from 2015) Revision

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  • Created on: 18-04-16 20:06
Exothermic reaction
Enthalpy of product is lower than reactants. Gives out hear. Negative value. Combustion is an example. Increase in temperature. Bonds are formed.
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Endothermic reaction
Enthalpy of product is higher than reacters. Energy is absorbed. Positive value. E.g photosynthesis, thermal decomposition. Decrease in temperature. Bonds are broken.
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Activation energy
Minimum energy required to start a reaction
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Standard states
298K, 101KPA, 1moldm23 - shown by flying saucer.
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The standard enthalpy of FORMATION
The energy change when one mole of a compount is formed in it's standard state from it's constituent elements in their standard states under standard condition. Elements=0 kmol-1
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The standard enthalpy of COMBUSTION
The enthalpy change when 1 mole of a substance reacts completely with oxygen under standard conditions.
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The standard enthalpy change of NEUTRALISATION
The enthalpy change when 1 mole of water is made by the neutralisation of an acid with an alkali under standard conditions
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Average Bond Enthalpy
The enthalpy change when 1 mol of gaseous covalent bonds are broken average over a range of compounds
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working out hear energy
q=mc x change in TEMP
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Enthapy change
q / n
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Hess's Law
Energy cannor be created or destroyed. If a reaction can take place by 2 routes and starting and finishing conditions are the same the total energy change is the same for each route
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Enthalpy using bond enthalpy
Sum of bond enthalpy of reactants - Sum of bond enthalpy of products
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Functional group
Group of atoms responsible for chemical properties of a molecule
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Bond angles and shapes of organic products
Alkane- Tetrahedral, 109.5, Alkene- Trigonal pleanar, 120, Alcohol- non linear, 104.5
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Properties of Alcohol
High bpt - Hydrogen bonds, Polar + Miscible,
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Elimination reaction
Alcohol --> Alkene remove H2o , concentrated H2SO4/ H3PO4
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Oxidation of alcohol
K2Cr2O7/ H2SO4 , colour change orange to green if oxidised. Distil --> aldehyde, reflux for carboxylic acid or ketone (2ndary alcohol) . TERTIARY ALCOHOL CANNOT BE OXIDISED
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Substitution reaction in alcohol
Alcohol --> haloalkane , NaCL/H2SO4w
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a compound with hydrogen and carbon only
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C-C single bonds onle
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C=C double bond
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Molecules with same molecular formula different structural formula
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Homlgous series
Family of compounds with the same functional group but each successive member diffeing by CH2
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Electron pair donor
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Electron pair acceptor
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Homolytic fission
Covalent bonds broken equally so each product recieves one pair of electron
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Heterolytic fission
Covalent bonds broken unequally so one product recives both eectrons and other forms ions
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Species with unpaired electrons
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Curly arrow
Shows the movement of a pair of electrons
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Alkene Bonds
sigma bond with high bond enthalpy ovelap and pi bond overlap sideways. It's a region of high electron density and has a low bond enthalpy
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Types of structural isomers
Chain, branched, functional group
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compounds with the same structural formula but different arrangement in atoms. E/Z or Cis/Trans isomerism occur because restricted rotation and 2 different group in each carbon around the double bond
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Alkene---> Alkane H2, Ni catalyst, >100*
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Unsymmetrical alkenes
Gives rise to 2 different products. Major and minor product when it reacts with hydrogen halides
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Alkene ---> Alcohol, steam, h3PO4, >100
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Major product
formed by the most stable carbocation. Tertiary carbocation is the most stable
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Weak Acid
Partially dissociates in water equilibrium is lies.
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H+ ion of an acid is replaced by a metal ion or NH4+
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Hydrated Salt Na2SO4. nH20
Anhydrous salt=NA2SO4 Water of crystallisation = nH2O
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Chemical Bond
Force that holds particles together (Ionic, Covalent, Metalic)
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Ionic Bonding
Electrostatic attraction between positive and negative ions (Metal + Non metal)
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Giant ionic lattice
Solid. Oppositely charged ions strongly attracted in all directions
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Properties of Giant Ionic substances
Fixed position. High boiling point. Soluble in Water. Mobile ions in solution can carry charge
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Covalent Bond
Electrostatic attraction between a positively charged nucleus and a shared pair of electrons. Average bond enthlpy can be used to mesure the strength
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Dative Bond
only one of the boded atoms provides both electrons being shared
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Electron pair repulsion theory
Electron pair repel each other so they are far apart as possible. Lone pair repulsion is stronger than bonding pairs.Shape is determined by no of lone and bonding pairs.
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Shapes and Bond angles
Linear=120, Trigonal Pleanar= 120. Tetrahedral= 109.5, Octahedral= 90, Pyramidal= 107, Non linear 104.5
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Intermolecular forces
Forces ocurring between molecules in simple covalent substances
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Induced Dipole Dipole Interactions
Non polar, temporary, constant movement of electrons creates an uneven districution of electrons and creates a dipole which cause dipoles in neighbouring molecules
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Permanent Dipole
Polar bonds, occurs due to different electronegativities in bonded atoms
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The power of attraction between a bonded atom and a pair of electrons in a covalent bond
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Non Polar
Symmetrical, no lone pairs on central atom, dipoles cancel out
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Uneven distribution of electrons, slightly charged, lone pair on central atom so dipoles do not cancel out
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Hydrogen bond
When a slightly positive hydrogen is bonded to slightly neagative N,O,F
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Anomalus properties of water
1) High BPT- Strong H bonds, 2) Ice is less dense tha water because H bonds holds molecules further apart creating space in between molecues
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Properties of Simple Covalent Bond
Low BPT, non polar simple insoluble in water, do not conduct electricity
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Giant Covalent (Graphite)
2 CV bond carbon, High bpt, delocalised electrons allows electrical conductivity, Insoluble in water, HEXAGONAL arrangment, soft
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Tetrahedral arrangment, 4 Carbon atom bonded, High mpt, Insoluble in water and do not conduct electricity, Brittle
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Metalic Bonding
Electrostatic atraction between positively charged ions and delocalised electrons
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Physical properties of Giant Metalic
High mpt, conduct electricity because of free electron, insoluble in water, Malleable/ductile
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Region of space that can hold up to 2 electrons, s (spherica), p (dumbell shape- 3 p orbital)
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Conditions and reagents for nucleophilic substitution
Warm NaOH
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Uses of haloalkane
polymers, cleaning solvent, aerosol, non stick pan, plastic bags
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CFC's and NO
catalyse the break down of ozone layer. Absorb UV radiation. CL +O3--->ClO+O2 . ClO + O ---> Cl + O2. overall equation O3 ---> O + 2O2
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Where is ozone layer found?
Earth's Stratosphere
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how easily a substance turns into gas
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Species formed during a reaction that reacts further to give the final product
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Target Molecule
The molecule that is the desired product
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Impurities and how to remove it
Acid- Add carbonate, Aldehyde- Add Cr2O72-/H+ , Organic product-separating funnel/run off, Water-Drying agent (Anhydrous salt CaCL2)
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Only collect product with the bpt of target molecule
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Fingerprint region
peaks below 1500cm-1 that aew unique for any given molecule
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IR Spectroscopy
Used to identify which functional groups are epresent in a given mlecule. Used to moniton air pollutoon drug detection, breathysers drunk drivers, quality control in persume production.
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First Ionisation energy
The energy needed to remove one elctron from each atom in one mole of gaseous atoms to make on emole og gaseous unipositive ion
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Second ionisation energy
Energy needed to remove 1 electron on each unipositive ion in one mole of gaseous unipositive ions to make one mole of gaseous dipositive ion
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Rate of reaction
Change in concentration of reactant or product per unt time
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Area under curve
Total number of particles
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Provides an alternative route by lowering activation energy
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Collision theory
For a chmical reaction to occur particle must collide in the same orientationwith Ea
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Activation energy
Minimum energy required for a collision to lead to a reaction
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Heterogenus catalyst
Different phases. Provides a surface for catalyst to work on. Adsorbtion of the molecules at the catalyc suface, chemical reaction weakens the bond and the desorption of the product molecules away from the catalyst
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Feautures of Equilibrium
Rates of forward and backwards reactions are equal. Concentrations of reactants and products are constant.
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Dynamic equilibrium (Closed System)
Conversion between product and reactants.NO exchange of matter or energy between the system and it's surroundings
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Heterogenus euilibrium
reactant and products are in different phases
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Homogenous equilibrium
reactan and prodcts are in different states
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Le Chatelier's principle
When a system under dynamic equilibrium is subjeted to a change the equilibrium will shift as oppose to the change
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Card 2




Endothermic reaction

Card 3


Minimum energy required to start a reaction


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Card 4


298K, 101KPA, 1moldm23 - shown by flying saucer.


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Card 5




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