Lesson 3 Chemical Reactions-1 PDF

Chemical Reactions Prepared by: Jenny Lou P. Atienza  Lesson Topics Type of Balancing Oxidation- Intermolecul Mole and Chemical Chemical Reduction ar forces Mass...

Chemical Reactions Prepared by: Jenny Lou P. Atienza  Lesson Topics Type of Balancing Oxidation- Intermolecul Mole and Chemical Chemical Reduction ar forces Mass Acid-Base Reactions Equation Donor-Acceptor calculation  Energy in Reactions In a chemical reaction, the total amount of energy in the universe at the end of a reaction, is the same as it was at the start of a reaction. Energy is conserved. When a chemical reaction occurs, energy is transferred either to or from the surroundings. 2 Classifications of Reaction: Exothermic Endothermi Reactions c Reactions Exother mic Exothermic reactions are reactions in which energy is given out to the surroundings, increasing the energy of the surroundings so they have more energy than they started with. There is a temperature increase. Example s Examples of exothermic reactions include: Many oxidation reactions Combustion reactions (burning) Most neutralization reactions  Uses Exothermic reactions have useful applications including self-heating cans and hand warmers. Endother mic Endothermic reactions are reactions in which energy is taken in during the reaction, meaning that the surroundings have less energy than they started with. There is a decrease in temperature. Exampl es Examples of endothermic reactions include: Thermal decomposition reactions Electrolysis  Use s An endothermic reaction is used in instant use ice packs. These are often used to treat sports injuries. Different Types of Reaction  Decomposition Reaction In a decomposition reaction, molecules or compounds break down into two or more than two simpler chemically new substances. For example, electrolysis of water. In the electrolysis of water, water breaks down into hydrogen and oxygen, which show completely different properties than water.  Combination Reaction In a combination reaction, two or more molecules are combined together chemically to form a new substance (compound). Combination and decomposition reactions are opposite of each other. For example, when sodium combines with chlorine forming sodium chloride  Combustion Reaction It is an exothermic reaction that releases energy, generally in the form of heat. It is a reaction between fuel and an oxidant (generally atmospheric oxygen) that produces smoke, water and heat generally. For example, when we burn methane, it gives carbon dioxide and water.  Neutralization Reaction In these reactions, acid and base react with each other and form salt and water. For example, hydrochloric acid reacts with sodium hydroxide (base) and forms sodium chloride (salt) and water.  Single Displacement Reaction In these reactions, more reactive metal displaces less reactive metal from its salt. In these reactions, products can be determined through reactivity series. Reactivity series is a series in which elements are arranged in decreasing order of their reactivity. It means the elements present at the top of this reactivity series are more reactive than the elements present at the bottom.  Double Displacement Reaction In these reactions, two aqueous ionic compounds exchange their ions (mostly cations) and produce two new compounds. For example, potassium nitrate reacts with aluminium chloride and forms aluminium nitrate and potassium chloride.  Precipitation Reaction In these reactions, an insoluble precipitate is formed. In precipitation reactions, two soluble salts in aqueous solutions are combined and form an insoluble precipitate.  Redox Reaction Oxidation- Removal of electrons (gaining Those chemical reactions positive charge) in which oxidation and Reduction- Gaining of reduction take place electrons (gaining simultaneously are called negative charge) redox reactions. Oxidation is the loss of electron, while reduction is the gain of electrons ACTIVITY TIME!  Balancing Chemical Equation Even though chemical compounds are broken up and new compounds are formed during a chemical reaction, atoms in the reactants do not disappear, nor do new atoms appear to form the products. In chemical reactions, atoms are never created or destroyed. The same atoms that were present in the reactants are present in the products – they are merely reorganized into different arrangements. In a complete chemical equation, the same number of atoms must be present on the reactant and the product sides of the equation.  Coefficient & Subscripts There are two types of numbers that appear in chemical equations. There are subscripts, which are part of the chemical formulas of the reactants and products: There are also coefficients that are placed in front of chemical formulas to indicate how many molecules of that substance are used or produced: Steps in Balancing Chemical Equation Write all the elements involve in the reaction Write the number of atoms in each element on the reactant side Write the number of atoms in each element on the product side Balance the equation by manipulating the coefficients of both reactant and product ACTIVITY TIME!  Redox Reaction An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species. An oxidation-reduction reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron. Redox reactions are common and vital to some of the basic functions of life, including photosynthesis, respiration, combustion, and corrosion or Rules for Assigning Oxidation State The oxidation state of an individual atom is 0. The total oxidation state of all atoms in: a neutral species is 0 and in an ion is equal to the ion charge. A chemical equation without a single atom is not considered as redox reaction The two species that exchange electrons in a redox reaction are given special names: 1.The ion or molecule that accepts electrons is called the oxidizing agent - by accepting electrons it oxidizes other species. 2.The ion or molecule that donates electrons is called the reducing agent - by giving electrons it reduces the other species. ACTIVITY TIME! Acid-Base Reaction An acid–base reaction is a chemical reaction that occurs between an acid and a base. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called acid–base theories, for example, Brønsted–Lowry acid–base theory. Their importance becomes apparent in analyzing acid– base reactions for gaseous or liquid species, or when acid or base character may be somewhat less apparent. Arrhenius, Bronsted, & Lewis Acid-Base Theories Arrhenius Theory: Acid releases H ions in the soluti Base releases OH ions into the solution Bronsted-Lowry Theory: Acids donates H ions Base accepts H ions Lewis Theory: Acids electron pair acceptor Base electron pair donor Properties of Acids 1. Acids taste sour. (Lemons) 2.Turns blue litmus paper into red. 3.Acidic solution: pH 7 4.Can conduct electricity in a solution. 5.Strong acids are strong electrolytes. 6.Weak acids are weak electrolytes. ACTIVITY TIME!  Intermolecular Forces Intermolecular forces, often abbreviated to IMF, are the attractive and repulsive forces that arise between the molecules of a substance. These forces mediate the interactions between individual molecules of a substance. Intermolecular forces are mainly responsible for the physical characteristics of the substance. Intermolecular forces are responsible for the condensed states of matter. The particles making up solids and liquids are held together by intermolecular forces and these forces affect a number of the physical properties of matter in these two states. 4 Major IMFs Ion-ion Interactions Ion-dipole Interactions Dipole-Dipole Interactions Van der Waals Force  Ion-ion Interaction Electrostatic attraction between electrically- charged particles is the strongest of all the intermolecular forces. These Coulombic forces (as they are often called) cause opposite charges to attract and like charges to repel.  Ion-dipole Interaction A dipole that is close to a positive or negative ion will orient itself so that the end whose partial charge is opposite to the ion charge will point toward the ion. This kind of interaction is very important in aqueous solutions of ionic substances; H2O is a highly polar molecule, so that in a solution of sodium chloride, for example, the Na+ ions will be enveloped by a shell of water molecules with their oxygen-ends pointing toward these ions, while H2O molecules surrounding the Cl– ions will have their hydrogen ends directed inward. As a consequence of ion-dipole interactions, all ionic species in aqueous solution are hydrated; this is  Dipole-dipole Interaction As two dipoles approach each other, they will tend to orient themselves so that their oppositely-charged ends are adjacent. Two such arrangements are possible: the dipoles can be side by side but pointing in opposite directions, or they can be end to end. It can be shown that the end-to-end arrangement gives a lower potential energy.  Van der Waals Interaction Van der Waals forces are driven by induced electrical interactions between two or more atoms or molecules that are very close to each other. Van der Waals interaction is the weakest of all intermolecular attractions between molecules.