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Chemistry Thermodynamics Notes Energy is defined as ____________________________________. • Energy can enter and leave a system in two ways: heat and work • System - the object of primary concern being studied • Surroundings - everything that surrounds the system Forms of Energy • ______________- energy an object possesses because of distortion (like a spring), position in a field of force (ex. gravity), or chemical bonds • ______________ - energy an object possesses because of its motion; KE = 1/2 mv2 Conservation of Energy and Heat Transfer • The law of conservation of energy states that energy cannot be created or destroyed in an ordinary chemical reaction, but the form of energy can change. • Heat can be transferred 3 ways: – _________________ (objects must be in contact) – _________________ (fluid motion of currents like warm air rising) – _________________ (electromagnetic waves such as the sun or a microwave oven) Heat is a form of energy associated with the ___________________________ of an object. • Heat is different from temperature; heat is transferred, and cannot be measured directly. Temperature can be measured directly. Temperature is a measure of the average ______________________ of the molecules in a system • Commonly measured with a thermometer or other device (temperature probe) • Objects with __________temperatures will transfer heat to objects of ___________temperature. Thermodynamics is the study of the flow of energy in chemical reactions (enthalpy, entropy, free energy) • Enthalpy: ∆H The heat content of a system at constant pressure • _____________ - when heat is transferred into a system from the surrounding; qsystem > 0 • _____________ - when heat is transferred out of the system into the surroundings; qsystem < 0 • Enthalpy Change Equation: H = Hproducts - Hreactants Sample Enthalpy Calculation CH4 (g) + 2 O2 (g) 2 (g) + 2 H2O (g) Substance CH4 O2 CO2 H2O ΔHof (kJ/mol) -74.8 0 -393.5 -241.8 ΔH = ΣΔHof (products) - ΣΔH of (reactants) ΣΔH of (products) = (1 mol)( -393.5 kJ/mol) + (2 mol)( -241.8 kJ/mol) = -877.1 kJ ΣΔH of (reactants) = (1 mol)( -74.8 kJ/mol) + (2 mol)(0 kJ/mol) = -74.8 kJ ΔH = - 877.1 kJ ( -74.8 kJ) = - 802 kJ EXOTHERMIC, because ΔH < 0 • Entropy: ∆S A measure of the ____________ of a system • Systems tend to move from ordered states with ___________ entropy, towards disordered states with ____________ entropy. • Free energy: ∆G Gibbs free energy, the maximum amount of energy that can be coupled to another process to do useful work • A process can ______________________________ occur if ∆G (the change in Gibbs free energy) for a process is negative. Ex. a ball rolling down a hill. • A process with a positive ∆G is considered ________________________________. Ex. a ball rolling up a hill. Units of Energy • Traditional Units of Heat – ____________ - the amount of heat required to raise the temperature of one gram of pure liquid water by one degree Celsius • SI Unit of Energy – _____________ - equal to a Newton-meter – used for all forms of energy – 1 calorie = 4.184 joules Specific Heat Capacity – Heat capacity per ___________ of a substance – units include cal/goC and J/goC – can be determined experimentally by determining the quantity of __________ transferred by a definite mass of the substance as its temperature rises or falls Heat Transfer Calculations • Q = m c T – Q = heat transferred in joules or calories – m = mass of substance in grams – c = specific heat capacity of substance – T = temperature change of the substance Phase Change Descriptions: _______________ the change from solid to liquid. _______________ the change from liquid to solid. _______________ the change from liquid to gas. _______________ vaporization from the surface of a liquid. _______________ vaporization from within as well as from the surface of a liquid. _______________ the change from gas to liquid. _______________ the change from solid to gas. _______________ the change from gas to solid. Heat Transfer for a Phase Change • Q = mΔHchange – Q = heat transferred in joules or calories – m = mass of substance in grams – ΔHchange = change in enthalpy of ____________________________ per gram • ex. ΔHfusion, ΔHevaporation, ΔHcondensation