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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