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32 Cards in this Set

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Extensive properties
-properties that are proportional to the size of the system
-if a property doubles when the systems are combined, the property is extensive.

-the study of energy and its relationship to macroscopic properties in chemical systems.
-based on probabilities, and are only valid for systems composed of a large number of molecules.

-examples are moles and volume.
Intensive properties
-properties that are independent of the size of the system.
-if you combine 2 identical systems and a property is the same for both the single system and the combined system, the property is intensive.
State Functions
-Properties that describe the state of a system, but not necessarily how the state was formed or what reaction pathway brought a state into being.
The two ways to transfer energy between systems
1. Heat
2. Work
Heat (q)
The natural transfer of energy from a warmer body to a cooler body.
Work
-Any energy transfer that is not heat.
3 heat forms
1. Conduction
2. Convection
3. Radiation
Conduction
-the thermal energy transfer via molecular collisions.
-requires direct physical contact
-higher energy molecules from one system transfer some of their energy to the lower energy molecules of the other system via molecular collisions.
-temperature difference in thermal conductivity is like pressure difference in fluids or potential difference in electricity.
Thermal conductivity
-the ability of an object to conduct heat
-depends upon the objects composition and its temperature.
-the rate of heat flow is constant across any number of slabs between two reservoirs.
-conservation of E!!
Convection
-thermal energy transfer via fluid movements.
-differences in pressure or density drive warm fluid air in the direction of cooler fluid.
Radiation
-thermal energy transfer via electromagnetic waves.
-all objects above 0K radiate heat
-objects that radiate heat faster also absorb heat faster, which means that it come to equllibrium with its environment more quickly.
PV work
w = PdeltaV(constant pressure)

-work as it applies to a chemical system at rest.
-at constant pressure, work is equal to the product of the pressure and the change in volume.
-A system at rest with no gravitational potential energy and no kinetic energy may still be able to do PV work.
-PV work takes place when a gas expands against a force regardless of whether or not the pressure is constant.
-there must be a change in volume!
Internal energy
-the collective energy of molecules measured on a microscopic scale.
-all the possible forms of energy imaginable on a molecular scale.
-may also be referred to as 'thermal energy' or 'heat energy'.
-if we have a closed system with no electric or magnetic fields, the only energy change will be in internal energy.
-for a reaction within a system involving no change in volume, there is NO work done and the change in internal energy is equal to the heat.
Temperature
-A state function that describes changes in thermal energy.
-An increase in thermal energy is due to increases in internal energy.
-An increase in thermal energy increases temperature.
-In a fluid, temperature is directly proportional to the translational kinetic energy of its molecules.
-ideally, can be thought of as the thermal energy per molecule or mole of molecules.
Average kinetic energy in a fluid
-given by the equation KEavg = (3/2)kT
Pressure of an ideal gas
-the random translational kinetic energy per volume. An intensive function.
-the greater the random translational kinetic energy of gas molecules per volume, the greater the pressure.
Enthalpy
Equation (under constant pressure conditions):

deltaH = deltaU + PdeltaV
H = entropy
U = internal energy
P=pressure
V=volume

-a man-made property that accounts for the extra capacity to do PV work.
-a state function
-measured in units of energy (joules) but not conserved like energy.
- we are interested mainly with CHANGE in enthalpy.
Standard state
-an element in its standard state at 25C is arbitrarily assigned an enthalpy value of 0J/mol.
-from this, enthalpy values are assigned to compounds based upon the change in enthalpy when the are formed from raw elements in their standard states at 25C.
Standard enthalpy of formation
-the change in enthalpy for a reaction that creates one mole of that compound from its raw elements in their standard state.
-for reactions involving no change in pressure, the change in enthalpy is equal to the heat.
Heat of reaction
delta(enthalpy of reaction) = delta(standard enthalpy of formation of products) - delta(standard enthalpy of formation of reactants).

-Since in many reactions in the lab, enthalpy approximates heat, the change in enthalpy from reactants to products is often referred to as the heat of reaction.
Hess's law
The sum of the enthalpy changes for each step is equal to the total enthalpy change regardless of the path chose.
Endothermic
-a reaction is endothermic if it has a positive enthalpy change.
Exothermic
-a reaction is exothermic if it has a negative enthalpy change.
Transition state
-the point in a reaction in which old bonds are breaking and new bonds are forming.
-represented in the 'peak' of the energy hill.
-occurs during the reaction collision.
Reaction intermediates
-products of the first step in a two step reaction.
Thermodynamics
-the study of energy and its relationship to macroscopic properties in chemical systems.
-based on probabilities, and are only valid for systems composed of a large number of molecules.
-CANNOT be applied to microscopic phenomena (for the most part).
Entropy (S)
-nature's tendency to create the most probable situation that can occur within a system.
-nature likes to lower energy of a system when it is high relative to the energy of the surroundings, but that means that nature likes to raise energy of a system when it is low relative to the energy of the surroundings.
-Entropy, not energy, dictates the direction of a reaction.
-equilibrium is the point in a reaction where the universe has achieved maximum entropy.
-entropy increases with number, volume, and temperature.
-an extensive property.
-Units: J/K
Second law of thermodynamics
-states that the entropy of an isolated system will never decrease because the odds of a decrease in entropy are so low.
-if we consider the universe as a system:
-the sum of entropy changes of any system and its surroundings equals the entropy change of the universe, which must be equal to or greater than zero.

delta(S)system +delta(S)surroundings = delta(S)universe, which is greater than or equal to zero.

-this indicates that entropy can decrease only if at the same time, entropy of the surroundings increases by a greater or equal magnitude.
Irreversible reaction.
-If the activation energy of a chemical reaction is sufficiently high for the reverse direction, the probability that it will occur may be sufficiently high for the reverse direction, the probability that it will occur may be sufficiently low that chemists call the reaction irreversible.
-a thermodynamically reversible reaction is one that stays infinitely close to a state of equilibrium at all times.
Third law of thermodynamics
-assigns by convention zero entropy value to any pure substance (either an element or a compound) at absolute zero and in internal equilibrium.
Thermodynamics
-the study of energy and its relationship to macroscopic properties in chemical systems.
-based on probabilities, and are only valid for systems composed of a large number of molecules.
-CANNOT be applied to microscopic phenomena (for the most part).
First law of thermodynamics
-energy of the system and surroundings is always conserved.