SUMMARY Factors that affect the rate of reaction. the number of reacting particles the number of effective collisions. Increasing CONCENTRATION

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1 SUMMARY Factors that affect the rate of reaction Increasing CONCENTRATION the number of reacting particles the number of effective collisions Increasing TEMPERATURE Increasing PRESSURE Increasing SURFACE AREA Addition of a CATALYST the KE of the reacting particles the frequency of effective collisions the volume of gases the [ ] of gases the frequency of effective collisions Exposes more area for reactions to occur Increases the frequency of effective collisions Provides a lower Activation Energy (E a ) -alternate pathway for the reaction LOWERS the activation energy NATURE of REACTANTS IONIC solutions are fast COVALENT substances are slower ENERGY AND CHEMICAL REACTIONS Potential Energy Energy stored in chemical substances Potential Energy of Reactants Amount of PE stored in the bonds of the REACTANTS Potential Energy of Products Amount of PE stored in the bonds of the PRODUCTS HEAT OF REACTION Amount of energy absorbed or released during a reaction ΔH of a reactions DIFFERENCE between the PE of the PRODUCTS and the REACTANTS -ΔH The PRODUCTS have LESS ENERGY that the reactants The reaction is EXOTHERMIC (releases heat) +ΔH The PRODUCTS have MORE ENERGY that the reactants The reaction is ENDOTHERMIC (aborbs heat)

2 Which conditions will increase the rate of a chemical reaction? (1) decreased temperature and decreased concentration of reactants (2) decreased temperature and increased concentration of reactants (3) increased temperature and decreased concentration of reactants (4) increased temperature and increased concentration of reactants Activation energy is required to initiate (1) exothermic reactions only (2) endothermic reactions only (3) both endothermic and exothermic reactions (4) neither endothermic nor exothermic reactions In order for a chemical reaction to occur, there must always be (1) an effective collision between reacting particles (2) abond that breaks in a reactant particlg (3) reacting particles with a high charge (4) reacting particles with high kinetic energy As the number of effective collisions between reacting particles increases, the rate of reaction (L) decreases (2) increases (3) remains the same What will change when a catalyst is added to a chemical reaction? (1) activation energy (2) heat of reaction (3) potential energy of the reactants (4) potential energy of the products The energy needed to start a chemical reaction is called (1) potential energy (2) kinetic energy (3) activation energy (4) ionization energy EXOTHERMIC reactants products + energy

3 ENDOTHERMIC reactants + energy products

4 How to determine information and questions you might be asked. After salt was dissolved in water, a student notices that the temperature of the water had gone up by 8. What is the best explanation for this? 1. The dissolving of the salt is endothermic, which releases heat. 2. The dissolving of the salt is endothermic, which absorbs heat. 3. The dissolving of the salt is exothermic, which releases heat. 4. The dissolving of the salt is exothermic, which absorbs heat. A student noticed this data for a reaction he conducted in a solution: Initial Temperature: 23 Final Temperature: 18 Which is true of the reaction he conducted? 1. It is exothermic with a -ΔH 2. It is exothermic with a +ΔH 3. It is endothermic with a -ΔH 4. It is endothermic with a +ΔH Another thing you will need to understand and determine is the TYPE OF REACTION FROM AN EQUATION. For example: Given the reaction: XW + energy W Which is true of this reaction? 1. The reaction is exothermic with -ΔH 2. The reaction is exothermic with +ΔH 3. The reaction is endothermic with -ΔH 4. The reaction is endothermic with +ΔH Given the reaction H2 + Br2 2HBr + 73 kj The heat of reaction, ΔH is because energy is released because energy is absorbed because energy is released because energy is absorbed

5 TABLE I TABLE I lists equations for selected physical and chemical changes and their ΔH (heat of reaction ) values YOU must be able to interpret information given on this table. For example: 2C(s) + 3H 2(g) C 2H 6(g) ΔH 84.0 POTENTIAL ENERGY DIAGRAMS Show changes in heat energy of substances over a course of a react

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