התנאים הנחוצים להתרחשות של תגובה כימית There are three conditions required for a chemical reaction to occur. 1. Collision: The reactants must collide. 2. Orientation: The reactants must align properly to . break and form bonds. 3. Energy: The collision must provide the energy of . activation.

מתי לא תתרחש תגובה? A chemical reaction does not take place if the collisions between reactant molecules do not have sufficient energy to break their bonds, or if molecules are not properly aligned.

אנרגית השפעול Activation energy is the minimum energy needed for a reaction to take place or break the bonds between atoms of reactants.

אנרגית השפעול The activation energy is the energy needed to convert reacting molecules into products.

חום התגובה The heat of reaction is the amount of heat absorbed or released during a reaction. is the difference between the energy of breaking bonds in the reactants and forming bonds in the products. has the symbol ΔH. ΔH = ΔHproducts − ΔHreactants

חבילות חמות וחבילות קרות

תגובה אקסותרמית In an exothermic reaction, the energy of the reactants is greater than that of the products and heat is released along with the products. the heat of reaction (ΔH) value is written with a negative sign (–) indicating heat is released.

תגובה אנדותרמית In an endothermic reaction, the energy of the reactants is lower than that of the energy of the products. heat is absorbed and used to convert the reactants to products and written with a (+) sign.

Heat of Reaction Summary סיכום חשוב Heat of Reaction Summary Reaction Energy Heat Sign of Type Change in Reaction ΔH Endothermic Heat absorbed Reactant side + Exothermic Heat released Product side –

תרגיל 1 Learning Check Identify each of the following reactions as exothermic or endothermic.

פתרון 1 Solution Identify each of the following reactions as exothermic or endothermic. Heat is a product. The reaction is exothermic. Heat is a reactant. The reaction is endothermic.

שיעור (קצב) התגובה The rate of reaction is determined by measuring the amount of reactant used up or product formed in a certain period of time. The rate or reaction is affected by temperature changes. changes in concentrations. the presence of a catalyst.

א. ההשפעה של הטמפרטוריה על שיעור התגובה At higher temperatures, the increase in kinetic energy causes the reacting molecules to move faster, more collisions occur, and more colliding molecules have sufficient energy to react and form products. For example, we refrigerate perishable foods to slow down the reactions that cause spoilage.

ב. ההשפעה של ריכוז המגיבים על שיעור התגובה Increasing the concentration of reactants increases the number of collisions and increases the reaction rate.

ג. ההשפעה של הוספת זרז על שיעור התגובה A catalyst increases the rate of a reaction. lowers the energy of activation. is not used up during the reaction.

Summary of Factors That Increase Reaction Rate סיכום הגורמים המעלים את שיעור התגובה Summary of Factors That Increase Reaction Rate

תרגיל 2 Learning Check State the effect of each on the rate of reaction as: 1) increases 2) decreases 3) no change A. increasing the temperature. B. removing some of the reactants. C. adding a catalyst. D. placing the reaction flask in ice. E. increasing the concentration of one of the reactants.

פתרון 2 Solution State the effect of each on the rate of reaction as: 1) increases 2) decreases 3) no change 1 A. increasing the temperature. 2 B. removing some of the reactants. 1 C. adding a catalyst. 2 D. placing the reaction flask in ice. 1 E. increasing the concentration of one of the reactants.

תרגיל 3 Learning Check Indicate the effect of each factor listed on the rate of the following reaction as 1) increases 2) decreases 3) none. 2 CO(g) + O2(g) 2 CO2 (g) A. raising the temperature B. adding O2 C. adding a catalyst D. lowering the temperature

פתרון 3 Solution Indicate the effect of each factor listed on the rate of the following reaction as 1) increases 2) decreases 3) none: 2CO(g) + O2(g) 2CO2 (g) 1 A. raising the temperature 1 B. adding O2 1 C. adding a catalyst 2 D. lowering the temperature