Industry condition is unfavorable LEARNING MODULE 5 PHYSICAL SCIENCE CHEMICAL KINETICS Developed by the Private Education Assistance under The GASPE Program of the Department of Education Concepcion Holy Cross College, Inc., Tarlac, 2316 G11| Q3 NOTICE TO THE SCHOOLS This learning module (LM) was developed by the Private Education Assistance Committee under the GASTPE Program of the Department of Education. The learning modules were written by the PEAC Junior High School (JHS) Trainers and were used as exemplars either as a sample for presentation or for workshop purposes in the JHS In-Service Training (INSET) program for teachers in private schools. The LM is designed for online learning and can also be used for blended learning and remote learning modalities. The year indicated on the cover of this LM refers to the year when the LM was used as an exemplar in the JHS INSET and the year it was written or revised. For instance, 2017 means the LM was written in SY 2016-2017 and was used in the 2017 Summer JHS INSET. The quarter indicated on the cover refers to the quarter of the current curriculum guide at the time the LM was written. The most recently revised LMs were in 2018 and 2019. The LM is also designed such that it encourages independent and self-regulated learning among the students and develops their 21st century skills. It is written in such a way that the teacher is communicating directly to the learner. Participants in the JHS INSET are trained how to unpack the standards and competencies from the K-12 curriculum guides to identify desired results and design standards-based assessment and instruction. Hence, the teachers are trained how to write their own standards-based learning plan. The parts or stages of this LM include Explore, Firm Up, Deepen and Transfer. It is possible that some links or online resources in some parts of this LM may no longer be available, thus, teachers are urged to provide alternative learning resources or reading materials they deem fit for their students which are aligned with the standards and competencies. Teachers are encouraged to write their own standards-based learning plan or learning module with respect to attainment of their school’s vision and mission. The learning modules developed by PEAC are aligned with the K to 12 Basic Education Curriculum of the Department of Education. Public school teachers may also download and use the learning modules. Schools, teachers and students may reproduce the LM so long as such reproduction is limited to (i) non-commercial, nonprofit educational purposes; and to (ii) personal use or a limited audience under the doctrine of fair use (Section 185, IP Code). They may also share copies of the LM and customize the learning activities as they see fit so long as these are done for non-commercial, non-profit educational purposes and limited to personal use or to a limited audience and fall within the limits of fair use. This document is password-protected to prevent unauthorized processing such as copying and pasting. Developed by the Private Education Assistance under The GASPE Program of the Department of Education Concepcion Holy Cross College, Inc., Tarlac, 2316 MODULE 5: CHEMICAL KINETICS Chemical kinetics, the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is to be contrasted with thermodynamics, which deals with the direction in which a process occurs but in itself tells nothing about its rate. Thermodynamics is time’s arrow, while chemical kinetics is time’s clock. Chemical kinetics relates to many aspects of cosmology, geology, biology, engineering, and even psychology and thus has far-reaching implications. The principles of chemical kinetics apply to purely physical processes as well as to chemical reactions. One reason for the importance of kinetics is that it provides evidence for the mechanisms of chemical processes. Besides being of intrinsic scientific interest, knowledge of reaction mechanisms is of practical use in deciding what is the most effective way of causing a reaction to occur. Many commercial processes can take place by alternative reaction paths, and knowledge of the mechanisms makes it possible to choose reaction conditions that favor one path over others. In this lesson, we shall learn to: ➢ Explain the effects of concentration, temperature, and particle size on the rate of reaction in terms of the collision theory. ➢ Define catalyst and describe its role in facilitating reaction. ➢ Name and explain the two requirements for an effective reaction to occur. ➢ Explain the collision theory in relation to how collision can affect reaction. Lesson 1: The Collision Theory The images you see above show a burning matchstick head and a rusting nail. Do you know that the two reactions are similar if not exactly the same? Both involve reaction in oxygen. The only difference is burning is a fast reaction while rusting is a slow reaction. While some reactions occur with so much drama, some are so quiet. In other words, the rate at which chemical reaction proceeds varies. If`you bring your attention once again to the photograph on the chapter opener, you come to realize that the rate of reaction or the speed at which a chemical reaction proceeds varies. Rates can be measured in terms of the changes occurring within certain intervals of time. Some maybe extremely slow that they may take weeks, months, or even years. Some may be happening so fast that they appear to be “spontaneous” and are usually accompanied by explosion. Some clues used by chemists to indicate that a chemical reaction may have occurred include the following: • • Change in color Production of light Developed by the Private Education Assistance under The GASPE Program of the Department of Education Concepcion Holy Cross College, Inc., Tarlac, 2316 • • • Formation of a solid (like a precipitate, smoke in air or a coating) Formation of bubbles Absorption or release Visible changes that are caused by chemical reactions are related to changes in the properties of individual atoms, ions, and molecules through a model called collision theory. This theory states that atoms, ions, and molecules can form a chemical bond when they collide. For this to happen, there are two requirements in order to combine chemically: ✓ Proper orientation of bonding atoms ✓ Sufficient energy for combination to occur Consider the following example, the reaction that occurs between O3 and NO molecules which happens in smog. O3 + NO O2 + NO2 For this reaction to occur, the O3 molecule and NO molecule must first collide with proper orientation. Examine two possible orientations as the molecules collide. If the two molecules are properly oriented, will the reaction occur automatically? Not necessarily, because the second requirement must be met: sufficient energy. For the reaction to occur, bonds of reactants must be broken so that new bonds can be form. The amount of energy required to break bonds in the reactant molecules differ for different reactants: thus it results in different reactions occurring at different rates. The minimum energy that colliding particles must have in order to react is called activation energy. Activation energy is a barrier that the reactants must overcome to be converted to products. As the reactants go through the reaction process an activated complex – a kind of transition state –is formed momentarily. Developed by the Private Education Assistance under The GASPE Program of the Department of Education Concepcion Holy Cross College, Inc., Tarlac, 2316 As discussed earlier, each reaction has its own specific energy involved and value from activation energy. Reactions with large activation energies tend to be slow, because a relatively small fraction of reactants have sufficient energy for an effective collision. Reaction with small activation energies tend to be fast, because a large fraction has sufficient energy for an effective collision. In some reaction energy is released as heat. This reaction is called exothermic reaction. However, not all reactions release energy. Some require a continuous energy absorbed from the surroundings. Such reactions are called endothermic reactions. These reaction profiles show the overall energy changes that accompany exothermic and endothermic reactions. In exothermic reactions, the energy difference is the energy released during the reaction. In endothermic reactions, the energy difference is the energy absorbed during the reaction. Lesson 2: Conditions that Affect Reaction Rates It has been discussed that for a collision to effect reaction, two requirements must be met: proper orientation and sufficient energy. However, there are conditions that can facilitate the work of two requirements. These are concentration, temperature, particle size and use of catalyst. Concentration The number of reacting particles in a given volume affects the reaction rate. Reaction may go faster when the concentration of one or more reactants per unit volume. This is because the molecules are closer Developed by the Private Education Assistance under The GASPE Program of the Department of Education Concepcion Holy Cross College, Inc., Tarlac, 2316 together, therefore, the number of collisions per unit time increases. The fraction of effective collision or the reactive number of collision to the total number of collision remains the same because the temperature and kinetic energy are constant. Particle Size Do you know the reason why sometimes you crush or powder a solid material before adding it to a liquid in order to dissolve? The reason is to expose more surface area of the solid to come in contact with the dissolving liquids, thus dissolving gets faster. With greater surface area, more interaction among reactants can occur. The effect of increasing the surface area of a solid in a reaction is similar to increasing the concentration. Temperature We know the process of solubility and chemical reactions proceed more rapidly at higher temperature. Temperature is a measure of the average kinetic energy of a substance. The average kinetic energy of a substance will rise in temperature increases the kinetic energy of a substance and also increases the fraction of effective collisions. As a consequence, more of the reactants attain the required activation energy and are able to overcome the energy barrier. Lesson 2: Catalyst A catalyst is a substance added to alter the pathway in which a reaction occurs without itself being consumed in the reaction. With a catalyst there is a lower-energy pathway with lower activation energy. The figure below shows how catalyst lowers the activation energy for a certain reaction, specifically an exothermic reaction wherein energy is released in the process. Note that the energy diagram shows two transition states, the reaction being catalyzed and which occurs in two steps with the first step forming an intermediate complex and catalyst having a lower energy that the two transition states. We can say that the catalyst lowers the activation energy for a reaction. Developed by the Private Education Assistance under The GASPE Program of the Department of Education Concepcion Holy Cross College, Inc., Tarlac, 2316 In living organisms, reactions are also catalyzed by catalysts known as enzyme. With these enzymes, life-sustaining chemical processes would be faster and occur relatively low temperature in plant and animal cells. Most enzymes are large protein molecules with large molar masses. Let us point out important characteristics of catalysts: they lower the activation energy of a reaction and they remain unchanged after the reaction is completed. Developed by the Private Education Assistance under The GASPE Program of the Department of Education Concepcion Holy Cross College, Inc., Tarlac, 2316
