Chapter 6 – Thermochemistry- Nature of Energy o Even though chemistry is the study of matter, energy affects mattero Energy is anything that has the capacity to do worko Work is a force acting over a distance Energy = Work = Force x Distanceo Heat is the flow of energy caused by a difference in temperatureo Heat and Work are the two different ways that an object can exchange energy with other objects- Classification of Energy o Kinetic Energy is energy of motion or energy that is being transferred o Thermal Energy is the energy associated with temperature Thermal energy is a form of kinetic energyo Potential Energy is energy that is stored in an object, or energy associated with the composition and position of the object Energy stored in the structure of a compound is potential- Some Forms of Energy o Electrical Kinetic energy associatedwith the flow of electricalchargeo Heat or Thermal Energy Kinetic energy associatedwith molecular motiono Light or radiant energy Kinetic Energy associatedwith energy transitions inan atomo Nuclear Potential energy in thenucleus of atomso Chemical Potential energy due to the structure of the atoms, the attachment betwee atoms, the atoms’ positions relative to each other in the molecule, or the molecules, relative position in the structure- Conservation of Energy o The 1st law of thermodynamics: Law of Conservation of Energy states that energy cannot be created nor destroyed.  When energy is transferred between objects, or converted from one form to another. You can therefore never design a system that will continue to product energy without some source of energy- Units of Energy o 1 Joule (J) is equal to the energy expended (or work done) in applying a force of one newton through a distance of 1 meter. 1 J = 1 N×M = 1kg×m×m/s2 = 1 kg×m2/s2 1 N = 1kg×m/s2o Calorie (cal) is the amount of energy needed to raise the temperate of one gram of water 1°C Kcal = energy needed to raise 1000 g of water 1°Co Energy Conversion Factors 1 Calorie (cal) = 4.184 joules (J) 1 Calorie (cal) = 1kcal = 1000 cal = 1 kcal = 4184 J 1 kilowatt-hour (kWh) = 3.60×106J- System and Surroundings o We define the system as a part of the universeon which we wish to focus attentiono Surroundings include everything else in theuniverse - Energy Flow and Conservation of Energy o Conservation of energy requires that the sum of the energy changes in the system and the surroundings must be zero- Internal Energy o The internal energy is the sum of the kinetic and potential energies of all of the particles that compose the system State function is a mathematical function whoseresult only depends on the initial and finalconditions, not on the process used- Energy Flowo- Energy Exchange o Energy is exchanged between the system and surroundings through heat and work Q = heat (thermal) energy W = work energy Q and W are NOT state functions, their value depends on the processo- Heat Exchange o Heat is the exchange of thermal energybetween the system and surroundingso Temperature is the measure of theamount of thermal energy within asample of mattero Heat flows from matter with hightemperature to matter with lowtemperature until both objects reach thesame temperature Thermal Equilibrium - Quantity of Heat Energy Absorbed: Heat Capacityo When a system absorbs heat, its temperature increaseso The increase in temperature is directly proportional to the amount of heat absorbedo The proportionality constant is called the heat capacity Units of C are J/°C or J/Ko Q = C×ΔTo The larger the heat capacity of the object being studied, the smaller the temperature rise will be for a given amount of heat. - Factors affecting Heat Capacityo The heat capacity of an object depends on its amount of water 200g of water requires twice as much heat to raise its temperature by 1°C as does 100g of watero The heat capacity of an object depends on the type of material 1000 J of heat energy will raise the temperature of 100g of sand 12°C but only raise the temperature of 100g of water by 2.4°C- Specific Heat Capacity o The specific heat capacity is the amount of heat energy required toraise the temperature of one gram of a substance 1°C Cs Units are J/(g×°C)o The molar heat capacity is the amount of heat energy required toraise the temperature of one mole of a substance 1°C- Classifying Heat Energy o The heat absorbed by an object is proportional to its mass and thespecific heat of the material Heat = (mass) x (specific heat) x (temp. change) q = (m) × (Cs) × (ΔT)-- Heat Transfer & Final Temperature o When two objects at different temperatures are placed in contant, heat flows from the material at the higher temperature to the material at the lower temperature until both materials reach the same final temperatureo The amount of heat energy lost by the hot material equals the amount of heat gained by the cold material-- Pressure – Volume Work o PV work is work caused by a volume change against an external pressureo When gases expand ΔV is +, but the system is doing work on the surroudings, so wgas is – o As long as the external pressure is kept constant -Workgas = External Pressure × Change in Volumegas w = -PΔV To convert the units to joules, use 101.3J = 1 atm L- Measuring ΔE, Calorimetry at Constant Volumeo Because ΔE = q + w, we can determine ΔE by measuring qand wo In practice, it is easiest to do a process in such a way thatthere is no change in volume, so w = 0  At constant volume, ΔEsystem = qsystemo The surroundings is called a bomb calorimeter and isusually made of a sealed, insulated container filled withwater qsurroundings = qcalorimeter = -qsystem- Bomb Calorimeter o Used to measure ΔE because it is a constant volumesystemo The heat capacity of the calorimeter is the amount of heatabsorbed by the calorimeter for each degree rise intemperature and is called the colorimeter constanto Ccal, kJ/°C- Enthalpy o The enthalpy, H, of a system is the sum of the internal energy of the system and the product of pressure and volume H is a state functiono H = E + PVo The enthalpy change, ΔH, of a reaction is the heat evolved in a reaction at constant pressure ΔHreaction = qreaction at constant pressureo Usually ΔH and ΔE are similar in value, the difference for reactions that produce or use large quantities of gas- Endothermic and Exothermic