CHAPTER 6 Thermochemistry E Eproducts final Ereactants initial Units of Energy 1 calorie cal energy needed to heat 1g H2O by 1 degree celcius 2 Joules J Conversion Factors 1cal 4 184J 1Calorie 1kcal 1000calories 1kJ 103J 1L atm 101J Work w w P V w work L atm P pressure atm V volume L 1st Law of Thermodynamics 1 Energy in the universe is constant 2 Energy is neither created nor destroyed 3 Energy of isolated system is constant Heat q energy transfer from 1 system to another 1L atm 101J Energy Change E q w System Open matter and energy move in out Closed energy moves in out but matter is fixed Isolated neither matter or energy moves in out Exothermic heat is given off lose heat H 0 Endothermic heat absorbed gain heat H 0 State Function depends ONLY on present condition not how you got there q lost q gained Heat Capacity 1 Heat Capacity J K or J oC Cs q T Cs heat capacity 2 Specific Heat Capacity qp mass x Cs x T mass g heat J temp oC Cs J g oC 3 Molar Heat Capacity J mol K Calculating Enthalpy H heat of reaction 1 Calorimetry Hrxn qp qp mass x Cs x T 2 Hess Law Reverse the equation change the sign Change the coefficient multiply by the coefficient Bond Enthalpies Hrxn Bonds Broken Bonds Formed 3 Bonds broken always Bonds Forms always negative Standard Heats Formation Hrxn HF 4 0 Products HF 0 Reactants Standard state 1atm 1 0M 298K all elemental elements have HF Reverse the reaction change the sign Multiply reaction by constant multiply HF 0 by same constant 0 0 How many joules are in a 24 pack of miller light assume 90Calories per can Calculate the work done on a system during the synthesis of ammonia when volume contracts from 8 6L to 4 3L at 44atm pressure N2 3H2 2NH3 What is the enthalpy change when 155g of CO2 are produced from combustion of propane Is the reaction endothermic or exothermic Given E 2045kJ and H 2043kJ Is the following reaction endothermic or exothermic BaOH2 NH4Cl H 40 15kj BaCl 2 2NH3 It requires 4 193kJ to increase the temperature of a computer from 25 heat capacity Cs o C to 30 3 o C What is the Calculate the heat transferred when a can of pepsi with a mass of 350g is cooled from 25 3 o C Heat Capacity H 2O 4 18 o C to Calorimetry 25 0mL of 1M H2SO4 solution reacts with 50 0mL of 1M NaOH The temperature o C The specific heat of both is 4 18 J g increases from 25 2O is H enthalpy 1 0g cm o C to 33 9 3 Calculate the heat of reaction o C and the density of H Calculate H for the following 2H2 N2 N2H4 H 95 4 kJ N2H4 H2 2NH3 H 187 6 kJ Calculate H for C s H 2O g CO g H C O2 CO2 2CO O2 2CO2 2H2 O2 2H2O 2 g H 393 kJ H 566 kJ H 483 6 kJ Calculate standard heats of reaction if we reversed the reaction 5 2 O2 2NH3 2NO 3H 0 Then solve for H F 2O H is we doubled the reaction and also Calculate standard heats of reaction H F 0 for MgCO 3 H 1095 8 kJ mol Calculate H F given the following bond enthalpies CH3OH 3 2O2 CO 2 2H2O
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