University:
High School
Course:
High School Chemistry
Academic year:

2020
Views:

69

Pages:

2
Author:

nosman7562q

Reactions that Release Energy Reaction Kinetics & Potential Energy Diagrams • These reactions are Reactions that Absorb Energy • These reactions are Exothermic Endothermic • system gains heat • the system loses heat • the surroundings cool down • The surroundings heat up 1 We know that for a reaction to occur: 1. molecules must collide to react. But, only a small fraction of collisions produces a reaction. Why? 2. Particles must collide with the correct orientation. 3. the right amount of energy • Particles lacking the correct site or necessary kinetic energy to react bounce apart unchanged when they collide. •Activation energy is the amount of energy needed to cause a reaction. •Collisions must equal or exceed the activation energy heat so H is positive • The reactants have less potential energy than the products A-- -B AB A+B AB Time A POTENTIAL ENERGY DIAGRAM: C + O2 → CO2 + 395 KJ Time H < 0 •Products have lower energy than reactants C + O2 • The reactants have more potential energy than the products Potential Energy A+B H = Energy of products – energy of reactants •Exothermic – the reaction releases heat so H is negative H > 0 Potential Energy • Potential Energy of the reactants • Potential Energy of the products • Activation Energy E – the amount of energy required to reach the transition state or activated complex from the reactant • Transition State, Ts (Activated Complex) – when bonds break and form and reactants become products • Enthalpy, H – science word for heat, Types of Energy Diagrams •Endothermic – the reaction absorbs A-- -B Energy Diagram Parts Energy Types of Energy Diagrams How Reactions Happen •Energy released •Exothermic 395kJ •ΔH = -395kJ CO2 •(Heat of Reaction) Reactants  Products 9 2/25/2020 A POTENTIAL ENERGY DIAGRAM: CaCO3 + 176kJ → CaO + CO2 Energy CaO + CO2 Potential Energy Diagrams •Products have higher energy than reactants • One thing that is not represented in these simple examples… Activation energy •Energy absorbed •Endothermic 176kJ CaCO3 Reactants Endothermic with Activation Energy However, adding 150kJ won’t make the reaction happen 100 kJ 250 kJ Activation Energy 150 kJ Products have 350kJ of PE ΔH = Heat of Reaction Minimum amount of energy required to start a reaction •ΔH = +176kJ Reactants have 200kJ of PE •(Heat of Reaction)  Products 10 Exothermic with Activation Energy Activation energy Reactants 40kJ ΔH Catalyst: something that reduces the amount of activation energy needed to Activation energy = 10kJ start a reaction – speeds up a reaction ΔH = 25kJ Activation energy with a catalyst Endothermic Reaction with a Catalyst Products15kJ Exothermic Reaction with a Catalyst Five Factors Affecting Reaction Rate Five Factors Affecting Reaction Rate 1) Nature of the Reactants: what the reactants are (solids, liquids or gases) 2) Temperature: Increasing temperature always increases the rate of a reaction. 3) Surface Area: Increasing surface area increases the rate of a reaction 4) Concentration: Increasing concentration USUALLY increases the rate of a reaction 5) Presence of Catalysts Catalyst: A substance that speeds up a reaction, without being consumed itself in the reaction