Transcript Equilibria - Calthorpe Park Moodle

Equilibria
⇌
Reversible Reactions
• In Reversible Reactions the products can react
to form the original reactants
• Equilibrium reactions refer to the forward
reaction (left to right) and the backwards
reaction
• A reversible arrow is used
⇌
Reaction conditions
• An equilibrium only occurs if the reaction is in
a closed system where nothing can get in or
out.
• In a dynamic equilibrium the forward reaction
and the backwards reaction occur at the same
time and rate.
Industry
• Changing the reaction conditions, changes the
equilibrium position and therefore the
amount of reactants or products.
• This is important in industry where many
products are made in equilibrium reactions.
The Haber Process
• Ammonia is made by the Haber Process
• Nitrogen + Hydrogen
•
N2
+
3 H2
⇌ Ammonia
⇌ 2 NH3
• Nitrogen is from the fractional distillation of
air and Hydrogen is obtained from methane.
Conditions for the Haber Process
• A high temperature increases the rate of reaction, but
reduces the yield of Ammonia because the forward
reaction to make ammonia is exothermic.
• A high pressure increases the rate of reaction, but is too
expensive.
• Increasing the pressure favours the side of the equilibrium
with the least number of gaseous molecules.
• Compromise temperature 450 oC and 200 atm pressure
are used.
Economics of the Haber Process
• Using an Iron catalyst does not affect the
position of the equilibrium, but it increases the
rate of reaction and reduces the cost of the
process. Iron is a cheap catalyst.
• Ammonia is cooled, liquefied and removed as
soon as it is made to stop it decomposing.
• Unreacted Nitrogen and hydrogen are recycled.
• Ammonia is used to make fertilisers.
Organic
Chemistry
C2H5OH
Hydrocarbons
• Organic molecules contain carbon compounds
• Alkanes and Alkenes are hydrocarbons
• Ethane, C2H6
Ethene, C2H4
Functional Groups
• A functional group is the part of the molecule
that is involved in chemical reactions.
• Replacing an H atom with a functional group
makes other organic compounds:
• Alcohols,
Carboxylic acids,
Esters
- OH
- COOH
- COOR
Alcohols
• Alcohols are a homologous series of
compounds containing the
– OH group.
• Ethanol, with a structural formula of C2H5OH.
• Displayed formula
• Ethanol is the alcohol found in drinks.
Properties of Alcohols
• They are Flammable and used as fuels
• Combustion of Ethanol :
C2H5OH + 3O2
→
2CO2 + 3H2O
• They react with Sodium to produce
Hydrogen, but this is slower than sodium
with water.
Oxidation of Alcohols
• They can be oxidised to Carboxylic acids by
boiling with potassium dichromate
• E.g. Ethanol makes Ethanoic acid (Vinegar)
Carboxylic Acids
• These are weak acids with pH values higher
than for strong acids.
• Strong acids are fully ionised, but weak acids
are partially ionised.
CH3COOH
⇌
CH COO
3
+
+ H
• Weak acids have a lower concentration of
+
Hydrogen ions, H .
Esters
• Carboxylic acids and Alcohols react to make
Esters.
• Carboxylic acid + Alcohol → Ester + Water
Ethanoic acid + Ethanol → Ethyl ethanoate + Water
CH3COOH + CH3CH2OH →CH3COOCH2CH3 + H2O
Concentrated Sulphuric acid is the catalyst.
Properties of Esters
• Ethanoic acid + Methanol ⇌ Methyl ethanoate + Water
• Esters are volatile – evaporate easily.
• They are sweet smelling and fruity.
• Uses include as perfumes and food additives