CHAPTER 9 Chemistry 101

Kinetics Kinetics is the field of chemistry that deals with the rates of chemical reactions and gives us the factors that affect rates and tells us how they work

Types of Reactions A Heterogeneous reaction at least one reactant is not mixed with the other reactants. The particles of at least one reactant consist of big clumps of atoms, ions, or molecules.

Formulas The following formula expresses the relationship between rate and speed.

This formula expresses the rate of a chemical reaction Rate of reaction = change in concentration = mol/L time s

Catalysts

Catalysts Catalysts also accelerate reactions, these are outside agents that in small concentrations accelerate reactions without themselves being changed. Reactions in plants and animals require special catalysts called enzymes.

Catalysts work in two ways: It can accelerate a reaction at the same temperature, or it can cause a reaction to take place at the same rate at a much lower temperature.

Continued… The catalyst permits the decomposition to happen at a lower temperature.

Collision Frequency Defined as the total number of collisions occurring between the reactant particles per unit of volume per second. An increase in temperature will also increase collision frequency because the increase in speed must result in more frequent collisions.

Kinetic Energy Kinetic energy becomes chemical energy during collisions between reactant particles. The minimum collision energy for a reaction is called the energy of activation symbolized as Eact

Continued… Some collisions are so insignificant that no distortion of electron clouds occur. This means little kinetic energy changes into potential energy. For every reaction there is

Rate of Reaction Is the number of collisions that are successful, each second in each unit of volume of the reaction mixture. A high energy of activation means a small fraction of successful collisions and a slow rate of reactions.

Continued… The heat reaction of an element is the net energy dismissed in other words the difference between the reactants and the products of a reaction. This is an example of the heat reaction of hydrogen and oxygen:

Continued… This reaction occurs when the conversion of some of the chemical energy in the electron-nuclei arrangements of carbon and oxygen into the molecular kinetic energy of CO2 molecules. This is an exothermic reaction, and either a rapid exothermic reaction or a slow exothermic reaction can be producing a heat of reaction.

The concept of pH An important thing to keep in mind is that the hydrogen ion concentration changes dramatically by a factor or 10 for each change of only one unit of pH.

Continued… PH refers to the molar concentration of hydrogen ions as opposed to the molar concentration of the solute contributing these ions. A good way to get an idea of the pH of a solution is to use an acid-base indicator or a combination of them. Litmus is blue above a pH of 8.5 and red below a pH of 4.5.

Litmus Paper

Continued… Commercial papers are another way to test the pH of a solution; their containers provide a color code so you can match the color produced by a drop of solution. If a solution tested produces a highly colored result we cannot use indicators.

Weak Acids For a weak acid, an acid ionization constant Ka is needed and is derived form the equilibrium constant. The equilibrium law for all monoprotic Bronsted acids is: Ka = [H+][A-] [HA]

Strong Bases Strong bases separate completely in water to release OH-, an example are sodium hydroxide.

Continued… Weak bases react with a small percentage of water, an example of a weak base is ammonia and bicarbonate. They both react with water to make some OH-.

pH of The Blood

pH of Blood Maintenance of the pH of the blood is very critical, if the pH becomes lower, this means that the acidity of the blood is increasing the condition is called acidosis. If the pH of the blood increases, which means that the blood is tending to become more basic or alkaline, the condition is called alkalosis.

BUFFERS

Buffers The principal buffer at work inside cells is the phosphate buffer which consists of a pair of ions. The principal buffer in blood is the carbonate buffer which is a carbonic acid in blood which is almost entirely in the form of CO2(aq).