ACSI HL Chemical Kinetics 2022 (Teacher)

IBDP Chemistry HL/ Chemical Kinetics Page 1 Anglo − Chinese School (Independent) Year 5 (2022) IBDP Chemistry HL (IBDP syllabus Topic 6 ) 6 .1 Collision theory and rates of reaction - Essential Idea: the greater the probability that molecules will collide with sufficient energy and proper orientation, the higher the rate of reaction . (IBDP syllabus Topic 1 6 ) 1 6 .1 Rate expression and reaction mechanism − Essential Idea: rate expressions can only be determined empirically and these limit possible reaction mechanisms. In particular cases, such as a liner chain of elementary reactions, no equilibria and only one significant activation barrier, the rate equation is equivalent to the slowest step of the reaction . 1 6 . 2 Activation energy − Essential Idea: the activation energy of a reaction can be determined from the effect of temperature on reaction rate. TEACHER COPY – WITH SUGGESTED SOLUTIONS TOPIC 6 CHEMICAL KINETICS

IBDP Chemistry HL/Chemical Kinetics Page 2 6.1 Collision theory and rates of reaction Nature of science: The principle of Occam’s razor (also known as Law of ecnonmy) is used as a guide to developing a theory – although we cannot directly see reactions taking place at the molecular level, we can theorise based on the current atomic models. Collision theory is a good example of this principle (2.7) It states that Pluralitas non est ponenda sine necessitate, “Plurality should not be posited without necessity.” (Encyclopedia Britannica). Newer theories need to remain as simple as possible while maximizing explanatory power. Understandings: • Species react as a result of collisions of sufficient energy and proper orientation. • The rate of reaction is expressed as the change in concentration of a particular reactant or product per unit time. • Concentration changes in a reaction can be followed indirectly by monitoring changes in mass, volume and colour. • Activation energy (Ea) is the minimum energy that colliding particles need in order to have successful collision leading to a reaction. • By decreasing E a, a catalyst increases the rate of a chemical reaction, without itself being permanently chemically changed. Applications and skills: • Description of the kinetic theory in terms of the movement of particles whose average kinetic energy is proportional to temperature in Kelvin. • Analysis of graphical and numerical data from rate experiments. • Explanation of the effects of temperature, pressure/ concentration and particle size on rate of reaction. • Construction of Maxwell –Boltzmann energy distribution curves to account for the probability of successful collisions and factors affecting these, including the effect of a catalyst. • Investigation of rates of reaction experime