HYDROCARBON - are organic compounds that contain carbon and hydrogen only
SATURATED HYDROCARBON - is a hydrocarbon with with single bonds
UNSATURATED HYDROCARBON - conatins carbon-to-carbon multiple bonds
ALIPHATIC HYDROCARBON - a carbon atoms joined together or in brached chains
ALICYLIC HYDROCARBONS - carbon atoms joined together in a ring structure
Chemical reactions occur at a definite rate determined by the reaction conditions. The rate of reaction may be increased by:
- Increasing temperature
- Increasing concentration of reactants
- Increasing surface area
Many reactions are subject to kinetic control.
Effect of Temperature rate of reaction
- Only those molecules having energy above a certain minimum value will react when they collide
- This minimum energy value is called the activation energy
- The activation energy can be thought of as anenergy barrier to the progress of the reaction.
ENERGY PROFILE DIAGRAMS
- The rate of reaction is directly related to the size of the activation energy.
The spread of energies in a sample of gas molecules is given by the Maxwell-Boltzmann distribution curve. Frequent collisions between molecules results in a spread of high and low energy molecules.
- At the lower temperature T1, the number of molecules with energy greater than activation energy is given by the purple shaded area.
- An increase in temperature to T2 results in a large increase in the number of such molecules.
- This increase is represented by the light blue shaded area.
- Therefore, the number of 'productive collisions' will be much greater at higher temperatures and so the rate will not be much
This is a high energy species in which old bonds are partially broken and new bonds are partially formed.
- A catalyst speeds up a chemical reaction without itself undergoing any permanent chemical change.
- They are usually specific to one particular reaction and they speed up both forward and back reactions equally.
- All types of catalyst work by providing an alternative pathway that has a lower activation energy than the original one.
In the presence of a catalyst a new pathway is created.
Homogenous catalysts function in the same state as the reactants (usually all in aqueous solution).
CH3COOH(aq) + C2H5OH(aq) → CH3COOC2H5(aq) + H2O(l) is catalysed by the acid: H+(aq)
Enzymes are important homogenous catalysts.
An instrument called a mass spectrometer is used to calculate relative atomic mass.
In a mass spectrometer:
- atoms are converted to positive ions;
- then deflected by electric and magnetic fields before being detected.
- The mass of the elements individual isotopes are found as well as their abundance.
From this data the Relative Atomic Mass can be found.
Equilibrium of reactions
Mechanism of bond breaking and making
A covalent bond can be broken in two ways:
a) Homolytic fission
- A:B → Ao + Bo
Produces free radicals which have an unpaired electron and are very reactive.
- A:B → A+ + B-
- A:B → A- + B+
dipoles come about when there is unequal distrubution between electronsin the molecule because some tend to attractor repel electrons
Chlorine has a greater share of the electrons due to the electronegativity it possesses:
Groups which are attracting electrons have a negative inductive (-I) effect. They give rise to electron deficient atoms Cδ+.
Groups which are electron repelling have a positive inductive (+I) effect. They give rise to electron rich carbon atoms Cδ-.
Nucleophiles: Attack centres of low electron density (nucleus loving). They possess a lone pair of electrons and are usually negatively charged.
Examples include: H2O, ROH, OH-, RO-, Br-, NH3, RNH2, CN-.
Electrophiles: Attack centres of high electron density (electron loving) The are capable of accepting a lone pair of electrons and are usually positively charged.
Examples include: H+, Br+, R-N=N, CN-.
FUNCTIONAL GROUP - the part of the organic molecule resposible for its reactions
molecules with same functional group react in a similar way
HOMOLOUS SERIES- series of compound with same functional group but with each successive member differing by CH2
ALKANES-are homologous series with the general formula CnH2n+2
addition polymerisation, alkenes add to themselves.
The alkene is the repeating unit