UNIT4DAY2-LaB Page 1 UNIT4DAY2-LaB Monday, November 12, 2012 10:00 PM Vanden Bout/LaBrake CH301 THERMODYNAMICS Quantifying Heat Flow Physical Change UNIT 4 Day 2 Important Information LM28 & 29 DUE Th 9AM HW10 DUE T 9AM EXAM 3 WRAPPER POSTED LATER TODAY OPEN 1 WEEK CH302 Vanden Bout/LaBrake Spring 2012
UNIT4DAY2-LaB Page 2 What are we going to learn today? Quantify Change in Energy by Quantifying Heat Derive State Function - Heat Flow at Constant Pressure Calorimetry Quiz: CLICKER QUESTION 1 When I think of types of energy, I think: a) KE and PE are the same as heat & work b) PE and KE are the same as heat & work c) PE and KE are the only two forms of energy d) Heat and work are the only two forms of energy
UNIT4DAY2-LaB Page 3 When I think of types of energy, I think: WHAT IT IS: PE - energy due to position or composition KE - energy of the motion of an object or particle HOW IT MOVES: Heat - transfer of energy from a hotter body to a colder body Work transfer of energy via applied force over distance First Law of Thermodynamics LAW OF CONSERVATION OF ENERGY UNIVERSE = SYSTEM + SURROUNDINGS YOU DEFINE YOUR SYSTEM, EVERYTHING ELSE IS SURROUNDINGS ΔU = q + w
CONCEPTUALIZE ENERGY ON THE MOVE THINK ABOUT A POWER PLANT FUEL WATER STEAM TURBINE GENERATOR How much energy does it take to boil enough water to generate enough steam to continue to make enough steam to generate enough electricity for the UTcampus? REACTANTs PRODUCTS ΔU =? HEAT = q 1 calorie = quantity of heat needed to raise the temperature of 1 gram of water 1 C. 1 Joule = 1 N force over 1 m MODEL & QUANTIFY HEAT Joule is famous because he found the relationship between heat and energy. He found by dropping weights, moving a paddle and noting the increase in temperature of water that 1 cal = 4.164 J. Measure changes in T of water and correlate that to energy in or out of a system! CONCEPTUALIZE ENERGY ON THE MOVE LARGE BEAKER OF WATER ON HOT PLATE SMALL BEAKER OF WATER ON HOT PLATE UNIT4DAY2-LaB Page 4
CONCEPTUALIZE ENERGY ON THE MOVE LARGE BEAKER OF WATER ON HOT PLATE SMALL BEAKER OF WATER ON HOT PLATE Thermal Energy = Kinetic Energy of the Particles (which has to do with the T) Heat Capacity = heat absorbed increase in temperature CONCEPTUALIZE ENERGY ON THE MOVE Thermal Energy = Kinetic Energy of the Particles (which has to do with the T) Heat Capacity = heat absorbed increase in temperature Which beaker had the higher Thermal Energy? a) LARGE b) SMALL Which beaker had the higher Heat Capacity? a) LARGE b) SMALL QUANTIFY ENERGY ON THE MOVE Measure the heat transferred into or out of a system using heat capacity, C. C x ΔT = q Specific heat capacity UNIT4DAY2-LaB Page 5
UNIT4DAY2-LaB Page 6 C x ΔT = q Specific heat capacity Molar heat capacity DEMONSTRATE ENERGY ON MOVE Ice water water Boiling water QUANTIFY ENERGY ON MOVE Ice water water Boiling water q = C specific x ΔT x mass
UNIT4DAY2-LaB Page 7 q = C specific x ΔT x mass Poll: CLICKER QUESTION 2 Think about the two systems in which the temperature is remaining constant. In these cases the thermal energy is being transferred from the hot plate: a) To the surroundings, bypassing the water/beaker system b) To an increase in thermal energy (kinetic energy) of the water/beaker system c) To an increase in potential energy of the water/beaker system. d) Is not being transferred, if T doesn t change, then there is no flow of heat energy.
UNIT4DAY2-LaB Page 8 Enthalpy of Physical Change heat is going into or out of the system. The heat is transferred into potential energy (change of position) of the particles Enthalpy of Vaporization ΔH vap Enthalpy of Fusion ΔH fus Enthalpy of Sublimation ΔH sub WHAT ON EARTH IS H? WHERE DID THAT COME FROM? q p = Δ Energy H (Enthalpy) = U (Internal Energy) + PV Determine ΔH if you can measure q p ΔH = q p QUANTIFY ENERGY ON MOVE Ice water water Boiling water
Temperature UNIT4DAY2-LaB Page 9 q = ΔH fus x moles q = ΔH fus x moles q = C specific x ΔT x mass HEAT CURVE FOR COLD ICE STEAM 100 0 ADD HEAT HEATING CURVE
UNIT4DAY2-LaB Page 10 POLL: CLICKER QUESTION 3 The molar heat of fusion of Na is 2.6 kj*mol -1 at its melting point, 97.5 ºC. How much heat must be absorbed by 5.0 g of solid Na at 97.5 ºC to melt it? POLL: CLICKER QUESTION 4 Calculate the amount of heat that must be absorbed by 50.0 g of ice at - 12.0 C to convert it to water at 120 C. The set up for the question above should have q calculation steps: a) 1 step b) 3 steps c) 4 steps d) 5 steps e) 6 steps
2+ - UNIT4DAY2-LaB Page 11 MODEL & QUANTIFY HEAT - USE HEAT CAPACITY TO CALCULATE HEAT GIVEN OFF OR ABSORBED BY CHEMICAL CHANGE HEAT = q Measure q CALORIMETER LOOK AT DEMONSTRATION CaCl 2 dissolved in water NO VOLUME CHANGE..so only q.. Give you ΔU HEAT FLOW IN OR OUT CAN TELL US ABOUT CHANGE IN INTERNAL ENERGY! Calorimetry-science of measuring heat Constant pressure & constant volume: No work is done, so ΔU = q + w ΔU = q + 0 ΔU = q POLL: CLICKER QUESTION 5 Look at the following physical change:
UNIT4DAY2-LaB Page 12 POLL: CLICKER QUESTION 5 Look at the following physical change: CaCl 2 (s) Ca 2+ (aq) + 2Cl - (aq) From the calorimeter observation which is lower in energy? a) LHS b) RHS POLL: CLICKER QUESTION 6 In this case assuming.. Water and a temperature change of.. Calculate q. Calculate heat of reaction
UNIT4DAY2-LaB Page 13 But what if there is work? ΔU = q + w Bomb type calorimeter-constant volume measurement ΔU = q + w In this case volume is controlled so no work can be done, w=0. ΔU = q
UNIT4DAY2-LaB Page 14 WHAT HAVE WE LEARNED TODAY? Heat vs Thermal Energy Quantify heat transfer New Thermodynamic State Function ΔH = q p Calorimetry Tool used to experimentally determine heat flowing into or out of a system
UNIT4DAY2-LaB Page 15 Learning Outcomes Calculate change in enthalpy for physical change in T and Phase Change Understand the concept of heat capacity, specific heat capacity and molar heat capacity Explain the difference between coffee cup calorimeter and bomb type calorimeter Understand the concept of change in enthalpy Calculate change in enthalpy, ΔH, and change in internal energy, ΔU, based on raw calorimeter data Calculate q for various processes