Kinetics and Equilibria

  • Created by: Pope1912
  • Created on: 07-04-15 15:27

Reaction Rates and Catalysts

Particles must collide inorder to react. In liquids and gases the particles are always moving a colliding with eah other. A reaction won't take place between the two particles unless...

They collide in the right direction and they collide with at least the minimum amount of kinetic energy. 

This is called collison theory.

The minimum amount of kinetic energy particles need to react is called the activation energy.This is the energy required to break the bonds to enable the reacction to begin.

Reactions with low activation energies often happen easily. But higher activation energies require high amounts of energy.

Not all molecules have the same amount of energy and the Maxwell-Boltzmann distribution graph is used to show these scientific observations. 

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Reaction Rates and Catalysts

Increasing temperatures makes the reactions much faster. The particles gain kinetic energy and move faster. 

A greater proportion of molecules will ave at least the activation energy and be able to react. This changes the shape of the Maxwell-Boltzmann distribution curve - it moves ut over to the right.

The area under the curve reamins the same!

Small increases in temperature can lead to large increases in rate of reaction. 

Increasing nconcentration also increases the rate of reaction. 

The particles, on average, become closer together. This increases the number of collisions and therefore the chances they have to react.

If the reaction is between gases then increasing the pressure works in the same way. 

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Reaction Rates and Catalysts

Catalysts increase the rate of reaction. 

A catalyst increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy. The catalyst is chemically unchanged at the end. of the reaction.

Catalysts don't get used up so we only require a small amount. 

Many will only work with a single reaction.

Catalysts help save money in industrial processes. 

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Reversible Reactions

Reversible reactions can reach dynamic equilibrium.

As the reactions get used up the forward reaction slows down.

As more product is formed the reverse reaction speeds up.

After a while the forward and reverse reactions will be going at excatly the same rate - this is dynamic equillibrium. This can only happen in a closed system where nothing can get in or out.

Le Chatelier's principle predicts what will happen if the conditions are chaanged.

By changing the concentration, temperature or pressure you change the position of eqilibrium meaning you end up with different amounts of product and reactants at equilibrium. 

If it moves to the left you get more reactants!

If it moves to the right you get more products!

If there is a change in concentration, temperature or pressure the eqilibrium will move to help to counteract the change in conditions. 

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Reversible Reactions

Catalysts do not effect the position of equilibrium.

They cannot increase the yeild but they do mean that eqilibrium is reached much sooner. 


If you increase the concentration of a reactant the equilibrium trys to get rid of the extra reactant. It does this by making more product. Equilibrium moves to the right.

Increasing the concentration of the product causes equilibrium to remove the extra product. Equilibrium moves to the left.

Decreasing concentrations has the opposite effect.

Pressure. (only effects equilibira involving gases)

Increasing pressure shifts the equilibrium to the side with fewer gas molecules. This reduces the pressure.

Decreasing pressure shifts the equilibrium to the side with more gas molecules. This raises the pressure.

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Reversible Reactions


Increasing the temperature causes equilibrium to shift in the endothermic direction to absorb the heat. 

Decreasing the temperature causes equilibrium to shift in the exothermic direction to replace the heat.

If the forward reaction's endothermic the reverse reaction is exothermic.

Ethanol can be formed from ethene and steam.

C2H4 + H2O <---> C2H5OH

This reaction is carried out at 60-70 atmospheres and 300 degrees with a catalyst of phosphoric acid.

Lower temperatures favour the forward reaction - more ethene and steam is converted to ethanol.

300 degrees is a comprimise between reaction rate and maximum yeild.

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Reversible Reactions

Higher pressures favour the forward reaction so a pressure of 60-70 atmopheres is used. High pressures move the reaction to the saide of the reaction with fewer molecules of gas. 

High pressures are expensive so 60-70 is a comprimise between maximum yield and costs.

Recycling ethene also saves moeny. Unreacted ethene is seperated from the liquid ethanol and recycled back to the reactor. 

Methanol can be produced from hydrogen and caarbon monoxide.

2H2 + CO <---> CH3OH

pressure - 50-100 atmospheres, temperature - 250 degrees, catalyst - copper, Zn oxide and Al oxide

Methanol is mainly used to make other chemicals but can be used as car fuel.

Ethanol and methanol are the greener alternative to petrol and are both carbon neutral. 

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