Review Chapter 6: Oxidation & Reduction Reactions

1. Review Chapter 6: Oxidation & Reduction Reactions Chemistry: The Molecular Nature of Matter, 6th edition By Jesperson, Brady, & Hyslop

2. Chapter 7 Concepts • Be familiar with Potential and Kinetic Energy • Potential Energy changes as bonds break and form • Average KE is proportional to Temperature • Conservation of Energy • Define system vs surroundings • Track direction of heat transfer between system and surroundings • Heat capacity calculations • Specific heat calculations • Exothermic vs Endothermic • Heats of reactions: • Calorimetry problems, qvvsqp • First Law of Thermodynamics • Define Enthalpy • Enthalpy calculations: • Hess’s law • ΔHfΔHrxn

3. Memorize E = Efinal – Einitial • T (K) Avg KE = ½ mvavg2 A calorie (cal) • Energy needed to raise the temperatureof 1 g H2O by 1 °C • 1 cal = 4.184 J (exactly) • 1 kcal = 1000 cal • 1 kcal = 4.184 kJ • 1 Cal = 1000 cal = 1 kcal • 1 kcal = 4.184 kJ Sum of all H°fof all of the products Sum of all H°fof all of the reactants q = C ×t H°reaction= – q = s m  t Potential Energy Kinetic Energy Total Energy Work = –P × V = + E = q + w • H = E + PV

4. Endothermic & Exothermic System heat Surroundings ENDOTHERMIC Heat + Reactants  Products Products have stronger bonds and therefore a higher potential energy then Reactants. Heat is absorbed by the system. ΔE + ΔH + PE decreases as bonds form PE increases as bonds break PE ENDOTHERMIC Heat absorbed Reactants Heat released EXOTHERMIC Products EXOTHERMIC Reactants  Products + heat Products have weaker bonds and therefore a lower potential energy then Reactants. Heat is released by the system. ΔE - ΔH - System heat Surroundings

5. System & Surroundings System heat qsystem = –qsurroundings Surroundings Constant Volume qv ΔE Constant Pressure qp ΔH Open system Closed system

6. Hess’s Law • Hess’s Law of Heat Summation • Going from reactants to products • Enthalpy change is same whether reaction takes place in one step or many Reactants Sum of Enthalpies from steps in path 2 = Path 1 Enthalpy Path 2 step b Path 1 Path 2 step b Products

7. Manipulating Thermochemical Rxns aA(state) + bB(state)  cC(state) + dD(state)ΔH • When equation is reversed, sign of H°rxn must also be reversed. • If all coefficients of equation are multiplied or divided by same factor, value of H°rxn must likewise be multiplied or divided by that factor • Formulas canceled from both sides of equation must be for substance in same physical states

8. Strategy for Adding Thermochemical Rxns • Choose most complex compound in equation for one-step path • Choose equation in multi-step path that contains that compound • Write equation down so that compound • is on appropriate side of equation • has appropriate coefficient for our reaction • Repeat steps 1 – 3 for next most complex compound, etc. • Choose equation that allows you to • cancel intermediates • multiply by appropriate coefficient • Add reactions together and cancel like terms • Add energies together, modifying enthalpy values in same way equation modified • If reversed equation, change sign on enthalpy • If doubled equation, double energy