Rates of reactions Flashcards
Activation energy
Minimum amount of energy for particles that collide with for a successful reaction to take place
catalyst
A substance that increases the rate of reaction without being changed in chemical composition or amount. Work by providing an alternate reaction pathway with a lower activation energy
collision theory
Reactions can only occur when collisions take place between particles that have sufficient energy
The particle orientation must be correct and collisions must have energy greater than or equal to the activation energy.
Effect of concentration on reaction rate
As conc increases, More molecules occur in the same volume and are packed closer together. Therefore collisions between molecules become more likely and chances are the successful collision increase. As a result rates of reaction increase.
effect of pressure on rate
Increasing pressure has similar effect as molecules are packed closer together into a smaller volume
effect of temp on rate
As temperature increases, the rate increases. Increasing temperature means an increase in kinetic energy of the molecules and they will move faster. Means that more molecules will have enough energy to react on collision meaning that the rate will increase
more molcules have required Ea
Effect of catalysts on rate
A catalyst will increase the rate of a chemical reaction without itself undergoing a permanent change.
molecules in a gas
Moving constantly at different speeds so energy of each molecule varies greatly
Since molecules collide frequently, a molecule that has been knocked, can move quicker w greater energy than before
Molecule that has caused collision will slow down and hardly have energy
boltzman distribution
Shows distribution of molecular energies in a gas
Energies of a few molecules are almost zero but no molecules will have zero energy
Activation energy
kinetic Energy x axis
Number of molecules y axis
At a higher temperature
disrubuion
Average molecular energy will increase, The distribution flattens and the peak moves to the right with a lower height
The mean energy of molecules increase and there is a wider spread of values
This also means that more molecules have a higher activation energy and the rate increases
Catalyst on bolztman distribution
Curve is unchanged but Ea shifts to left
A greater proportion of colliding molecules will achieve activation energy
Homogeneous catalysts
Is in the same physical state as the reactants takes an active part in reaction
Typically involves liquid or substances in solution
Eg. Concentrated sulfuric acid
Aqueous iron (II) ions in the oxidation of iodide ions
Heterogeneous catalysts
Is in a different physical state from reactants
eg. Iron in the haber process for ammonia production
Vanadium oxide within sulfuric acid manufacture
Nickel in hydrogenation of unsaturated oils
catalyst in industry
relies on catalyst to reduce cost
Since catalysts speed up process by lowering activation energy, less energy is required for molecules to react and this saves energy costs
Also benefit for the environment- If less fossil fuel is burnt, less carbon dioxide will be released during energy production
catalysts saving money
Many plastics are formed under high pressure. Can be found to enable reaction to give good yield at low pressure, the industrial plant will not have to withstand high pressure and less robust materials can be used in construction therefore saving money
