Collision theorystates that particles must collide with sufficient energy in order to react.
The minimum energy required for a reaction to take place (a successful collision) is the activation energy,
The rate of reaction can be measured as: - the amount of reactant used up in a set time.-or the amount of product formed in a set time.
Collisions that result in a reaction are more frequent with an increase in:
tempreture
concentration of a solution
pressure in gas(es)
surface area of a solid.
Using a catalyst lowers the activation energy required for particles to react.
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Types of reaction
In an exothermic reaction, energy is transferred to the surroundings. Exothermic reactions give OUTenergy.
In an endorthermic reaction, energy is transferred from the surroundings. Endothermic reactions take IN energy.
If a reversible reaction is exothermic in direction, it is endothermic in the opposite direction, e.g: ammonium chlorideammonia + hydrogen chlorideORhydrated copper sulfate (blue)anhydrous copper sulfate (white) + water
Inreversible reactions, equilibriumisreachedat a point when therate of the reverse reactionbalances therate of the forward reaction.
Therelativeamounts of all the reactingsubstancesat equilibrium depend on thereaction conditions.
Optimum conditions for theHaber processare:
temperature at 450°C
pressure 200 atmospheres
iron catalyst
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Ions
When molten or dissolved in water, the ions in the ionic compounds are free to move.
In electrolysis, an electric current passed through an ionic compound in which ions are free to move breaks it down into its elements.
During electrolysis: positivemetal ionsgain electrons to form atoms, negativenon-metal ionslose electrons to form atoms and molecules.
Electrolysis of sodium chloride (common salt) solution makes hydrogen, chlorine and sodium hydroxide:
Each positivesodium ion is reduced to form an uncharged sodium metal:
Na^+ (aq) + e^- ----> Na (s)
Each negativechloride ion is oxidised to form an uncharged chlorine atom that shares electrons with another chlorine atom to form chlorine gas:
2Cl^- (aq) ---->Cl2(g) + 2e^2
OIL RIG:Oxidation Is Loss, Reduction Is Gain- of electrons
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Making salts
Metal oxides and hydroxides are bases and react with acids to form salts. Soluble bases are alkalies.
In neutralisation reactions, hydrogen ions and hydroxide ions react to form water:---------------------------------------> H^+ (aq) + OH^- (aq) ---> H20 (l)
Neutralisations always produce a salt:
acid + metal ---> metal salt + hydrogen
acid + ammonia ---> ammonium salt
acid _ soluble base ---> metal salt + water
acids + insoluble base ---> metal salt + water
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Making salts 2
Some metals can be reacted with acids to make salts. The reactivity series of metals shows wether a metal will react with an acid.
Insoluble salts can be made as precipitates when twosolutions are mixed together.
Ion impurities can be removed from the water supply by making them into insolublesalts, e.g. phosphate ions from washing powders can be removed using calcium ions to form insoluble calcium phosphate.
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