1.5. Kinetics.pdf

AQA Chemistry A-level 3.1.5: Kinetics Detailed Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0...

AQA Chemistry A-level 3.1.5: Kinetics Detailed Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 3.1.5.1 - Collision Theory Chemical reactions occur when particles of substances ​collide​. For a reaction to occur successfully, these collisions must have ​energy greater than or equal to the activation energy​ of the reaction and the ​particle orientation​ must be correct. Reaction Conditions The conditions of a reaction impact the collisions of the particles and can be altered to provide the particles with ​more energy​. Therefore the conditions can be changed to increase the likelihood of a collision occurring with sufficient energy to react in order to increase rate. 3.1.5.2 - Maxwell-Boltzmann Distribution Not all molecules in a substance have the same amount of energy. Their energies are distributed​ in a pattern called the ​Maxwell-Boltzmann distribution​: Changing the reaction conditions will ​alter the shape of the curve​ so that the number of particles with energy greater than the activation energy is different. The total ​area under the curve​ represents the ​total number of molecules​ in the sample, therefore it ​must remain constant​. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 3.1.5.3 - Effect of Temperature When a substance is heated,​ thermal energy​ is transferred to it. This energy is converted to kinetic energy​ and the molecules of the substance move ​faster and further​. Increased movement of the molecules means ​collisions will occur more often​ and with ​greater energy​. As a result, more collisions have energy greater than the activation energy and result in a reaction. Therefore​ increasing the reaction temperature will increase the rate of reaction​ as more collisions of greater energy occur in a given time. The Maxwell-Boltzmann distribution at an increased temperature ​shifts to the right​ so that a greater proportion​ of molecules have energy greater than or equal to the activation energy. Example: 3.1.5.4 - Effect of Concentration and Pressure When the concentration of a sample is increased, more molecules of substance occur in the same volume meaning they are ​packed closer together​. Therefore collisions between molecules become ​more likely​ and the chances of a collision occurring with energy greater than the activation energy increases. As a result, the rate of reaction increases. Increasing pressure has a similar effect as molecules are ​packed closer together​ into a smaller volume. The Maxwell-Boltzmann distribution is ​shifted to the right​. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 3.1.5.5 - Effect of Catalysts A catalyst is a substance that ​increases the rate of reaction without being used up​ in the reaction. It works by providing an ​alternative reaction path​ that requires a ​lower activation energy​ for the reaction to occur. The Maxwell-Boltzmann distribution curve is ​unchanged in shape​ but the ​position of the activation energy is shifted to the left​ so that a greater proportion of molecules have sufficient energy to react. Example: https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc