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

Chapter 7 Concepts 2  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, q v vs q p  First Law of Thermodynamics  Define Enthalpy  Enthalpy calculations:  Hess’s law  ΔH f ΔH rxn

Memorize Total Energy Potential Energy Kinetic Energy = + A calorie (cal) Energy needed to raise the temperature of 1 g H 2 O by 1 °C 1 cal = J (exactly) 1 kcal = 1000 cal 1 kcal = kJ 1 Cal = 1000 cal = 1 kcal 1 kcal = kJ  E = E final – E initial T (K)  Avg KE = ½ mv avg 2 q = C ×  t q = s  m   t Work = –P ×  V  E = q + w H = E + PV  H° reaction = – Sum of all  H° f of all of the products Sum of all  H° f of all of the reactants

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

System & Surroundings Open system Closed system System Surroundings heat Constant Volume q v ΔE Constant Pressure q p ΔH q system = –q surroundings

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 Products Path 1 Path 2 step b Path 2 step b Sum of Enthalpies from steps in path 2 = Path 1 Enthalpy

Manipulating Thermochemical Rxns aA (state) + bB (state)  cC (state) + dD (state) ΔH 1.When equation is reversed, sign of  H° rxn must also be reversed. 2.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 3.Formulas canceled from both sides of equation must be for substance in same physical states

Strategy for Adding Thermochemical Rxns 1.Choose most complex compound in equation for one-step path 2.Choose equation in multi-step path that contains that compound 3.Write equation down so that compound  is on appropriate side of equation  has appropriate coefficient for our reaction 4.Repeat steps 1 – 3 for next most complex compound, etc. 5.Choose equation that allows you to  cancel intermediates  multiply by appropriate coefficient 6.Add reactions together and cancel like terms 7.Add energies together, modifying enthalpy values in same way equation modified  If reversed equation, change sign on enthalpy  If doubled equation, double energy