Hanna Muri Chemistry Sem 1 2018.docx - Hanna Muri 2018 Chapter 1 Collision Theory Rate of reaction is determined by the number of successful collisions

Hanna Muri Chemistry Sem 1 2018.docx - Hanna Muri 2018...

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Hanna Muri 2018 Chapter 1 Collision Theory Rate of reaction is determined by the number of successful collisions in a given time. Greater number of successful collisions = to faster rate of reaction. States that for a reaction to occur: Reacting particles must collide Collision energy must equal or exceed activation energy (Ea) Must collide with suitable orientation (Transition State) Factors affecting reaction rate Concentration/partial pressure: if concentration of a reactant is increased, then there will be more particles in a given volume. Makes it more likely for reactant particles to collide, therefore more collisions. *Only for reactants in solution or gaseous phase. Pressure: pressure of a gas is due to force exerted by particles colliding with the walls of the container. An increase in pressure means more particles in a given volume. Thus, concentration of gas particles will increase and therefore more collisions between particles. Reverse happens at decrease of pressure. Temperature: Increased temperature means increased average kinetic energy. This means more particles will have sufficient energy for a successful collision. Increased kinetic energy associated with increased speed of particles, thus more frequent collisions. Surface Area: In solids, only exterior of particles can collide. If surface area is increased by division or crushing, more particles will be exposed and be available for collision. Catalysts: Provide an alternative, easier pathway for reaction. This means lower activation energy, so more particles will have sufficient energy for a successful collision. Nature of Reactants: Ionic reactions are rapid as they do not involve the breaking of bonds or electron transfer between reacting particles. Molecular reactions are slow since they involve breaking and bond formation. Collisions are often unsuccessful at room temperature due to insufficient activation energy. Energy Changes Exothermic: Loses heat to surroundings. There is a negative change in enthalpy. Some of the chemical potential energy stored in bonds is converted to particle kinetic energy. Causes increase in system’s temperature. Overall energy is conserved with chemical potential energy becoming ‘heat’ energy. Endothermic: Gains heat from surroundings. There is a positive change in enthalpy. Fall in temperature due to particle kinetic energy converted to chemical potential energy. Initially there is no change in enthalpy.
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Hanna Muri 2018 Chapter 2 Reversible Reactions Have a low activation energy for forward and reverse reaction Don’t go to completion as once the products form they react to reform reactants In closed systems, forward & reverse reactions compete with 1 another preventing the reaction from completing in either direction Equilibriums Properties: Reversible Dynamic Macroscopic properties are constant (colour, pressure, temperature) Physical Equilibrium Example: Water H 2 O (l) H 2 O (g) In a closed system, the vapor is unable to escape so it reverts back to a liquid. Therefore a
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  • Fall '18
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