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Presentation On Collision Theory Of Rate Reaction

Published in: Chemistry | Science
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This PPT is suitable for the IGCSE and O Level Chemistry students. It only provides theoretical background of the topic. The practice questions, worksheets and topical questions will be discussed during the tutoring sessions

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  1. Collision Theory of Reaction Rate Chemistry (IGCSE / O-Level)
  2. What will you learn in this lesson? • Collision theory • Describe and explain the effect on the rate of reaction of: (a) changing the concentration of solutions (b) changing the pressure of gases (c) changing the surface area of solids (d) changing the temperature (e) adding or removing a catalyst, including enzymes using collision theory • Effect of catalyst on the activation energy, Ea, of a reaction
  3. Collision Theory A theory that states that a chemical reaction takes place when particles of the reactant collide with sufficient energy to start the reaction Collision Theory particles must Correct orientation energy
  4. Collision Frequency • In Solids: Reaction only occurs when particles collide with the surface of liquid. Dividing the solid into smaller pieces expose more area for the other reactant to collide and react a lump'S i iron; mostofthe atoms, mofecoie fron atom Ifthe iron å$ in;smallbts. the collide with many more iron atoms, 'The iron now has a much bigger surface 'a rex The reaction between iron and «ygen is speeded up if the iron is in small pieces.
  5. Collision Frequency (contd.) • In Solutions: When solution are more concentrated, the speed of reaction is faster. The more concentrated solution has more particles in a unit volume. Hence, more chances of collision and reaction concentrated hydrochlorve asd : fie acid thefaster the rea±ion With the maonesitm.
  6. Collision Frequency (contd.) • In Gases: Increasing the pressure of gases has same effect as the increase concentration of solutions in pressure de i&thaepenvery high Col different •meecules frequent. Increasing the pressure of gases effectively increases the concentration of the gas.
  7. Collision Frequency (contd.) • Effect of Temperature: There are factors that an increase in temperature increases the rate of a reaction. 1 The increæedtemøerature means that the molecules are moving faster and therefore they collide more often. The frequency of collision Is Increased and so the rate of reacUon is faster. 2 AtthehEghertemperature, the particles have higher Hnetlcenerqy. lhls means thatwhen they collide more particles vill have the minin-•um amount of energy needed to react. At the higher temperature more of the collision will produce a reaction; there will be more successful collisions. The number of effective collisions Increases wtth tncreastng temperature. This second factor is the more important of the w,'o in explaining tha level of increased rate produced by raising the temperature of a reaction.
  8. Collision Frequency (contd.) b Concentration m Ore chance Of' particlescolliding more particles collide with more, energy Figure 8.21: collision theory can be used to exDlain how various factors affect the rate of reaction. Here we use the reaction between zinc and hydrochloric acid as an example.
  9. Activation Energy (Ea) Not every collision between particles in a reacting mixture produce a reaction. The minimum amount of energy required to break the previous bonds and forming new bonds is called activation energy. • Each reaction has its own different value of activation energy. • When particles collide, they must have a combined energy greater than this activation energy, otherwise they will not react. • Chemical reactions occur when the reactant particles collide with each Other.
  10. Action of a Catalyst A catalyst increases the rate of reaction by reducing the amount of energy that is needed to break the bond (activation energy). It tries to make sure that more collisions are likely to produce products reactants with cataWst One broad group of Catalyst works by adsorbing molecules onto a solid surface pathway
  11. Catalyst Analogy reactant(s) catalysed path pass route Reaction path uneatalysed path route product(s)