Reaction Kinetics and Equilibrium How compounds react with each other

Collision Theory A reaction is most likely to occur if reactant particles collide with the proper energy and orientation http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/animations/NO+O3singlerxn.html

Reaction Rate Affecting Factors Nature of Reactants Concentration Surface Area Temperature Presence of a Catalyst Pressure for Gases

Nature of Reactants Factors that contribute to reaction rate: - Electronegativity - Ionization energy - Atomic Radius.

Bonding on Rate of Reaction Covalent bonds require more energy during collisions due to a greater number of bonds needed to be broken and reformed. Ionic Bonds are faster to react and require less energy during a collision.

Concentration We measure concentration by the number of moles there are in a L of solution (Molarity). More moles = more collisions Ex: Burning paper. When the oxygen concentration is low the paper burns slowly. Raise the amount of oxygen the paper burns faster. http://www.coolschool.ca/lor/CH12/unit1/U01L01.htm

Surface Area The larger the surface area the easier it is to react because there is more chances for collision.

Temperature The average kinetic energy of molecules in a compound. The more molecules move the higher the temperature. Higher temperature results in more collisions

Presence of a Catalyst A substance whose presence increases the rate of a chemical reaction. Catalysts change (decrease) the activation energy which increases the rate of reaction

Activation Energy Activation energy is the minimum energy required to initiate a reaction. When particles collide with the right amount of activation energy it breaks the existing bond.

Energy Kinetic Energy (motion) – this the energy of work being done Potential Energy (static) – the potential for something to do work **Remember that there are many types of energy: - electrical - thermal - mechanical - electromagnetic - nuclear

Endothermic vs. Exothermic Reactions Exothermic (exit) reactions give off heat energy during a chemical reaction Endothermic (enter) reactions absorb heat energy during a chemical reaction http://schools.matter.org.uk/Content/Reactions/BondActivation.html

Potential Energy Diagram Used to show the energy released or stored in endothermic and exothermic reactions http://www.saskschools.ca/curr_content/chem30/modules/module4/lesson4/potentialenergydiagram.htm

Reading Energy Diagrams THE Y AXIS – Potential energy of the reaction THE X AXIS – Reaction as it takes place over time CURVE – Represents the potential energy at each step of a chemical reaction

Reading Energy Diagrams ENTHALPY – Heat of reaction SUBTRACT THE VALUES ON THE Y AXIS, FINAL – INITIAL EXOTHERMIC REACTION – energy given off during a reaction LOOK AT THE CURVE AND SEE IF IT ENDS AT A LOWER VALUE

Reading Energy Diagrams ENDOTHERMIC – energy is absorbed during a reaction LOOK AT THE CURVE AND SEE IF IT ENDS AT A HIGHER VALUE ACTIVATION ENERGY – The amount of energy needed to reach the peak of the curve SUBSTRACT THE ENERGY AT THE PEAK OF THE CURVE FROM THE INITIAL ENERGY

Equilibrium The rate at which the products are formed is at the same rate that the reactants are formed. Three Types of equilibrium: Phase Equilibrium Solution Equilibrium Chemical Equilibrium

Rate of Reaction at Equilibrium As products are formed the amount of reactants decreases. We can find the rate of reaction by the equation: Δ [M products] = Δ [M reactants] Δ Time Δ Time

Equilibrium Constant Keq Expressed as a numerical value, relates the amount of reactants to products at equilibrium Keq = [products]n [reactants]n aA + bB cC + dD Keq = [C]c [D]d [A]a [B]b http://www.chem.uncc.edu/faculty/murphy/1252/Chapter15/sld005.htm

Heat of Reaction (Enthalpy) Heat of Reaction – energy stored or released during a reaction. ΔH = H Products – H Reactants

Known Heat of Reactions (ΔH) Table I lists heats of reactions at STP. ΔH = “-” value for exothermic reactions ΔH = “+” value for endothermic reactions Heat of formation (ΔHf)= amount of energy released when a mole of substance is formed from it’s elements

Entropy The measure of the randomness or disorder of a system’s energy. The greater the randomness the greater the entropy.

Entropy of Substances As a substance goes from solid to liquid to gas, entropy increases. Systems in nature tend to undergo changes toward low energy and high entropy

Spontaneous Reactions Two factors help determine if a reaction will react spontaneously: Decrease in Enthalpy ΔH (potential energy) exothermic reaction Increase in Entropy ΔS (random release in energy) as it goes from a solid – liquid – gas

Gibbs Free Energy For a reaction to be spontaneous the sign of ΔG (Gibbs Free Energy) must be negative. ΔG = ΔH – TΔS ΔH = Change in enthalpy T = Temperature in Kelvin ΔS = Change in entropy