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# EK Chem 3

### thermo

Question | Answer |
---|---|

extensive properties | properties that are proportional to the size of the system |

intensive properties | properties that are independent of the system |

state function | pathway independent, the state property going from 1 state to another is the same regardless how system was changed |

heat | movement of energy via conduction, convection, or radiation - always from hot to cold |

convection | thermal energy transfer via fluid movements |

radiation | thermal energy transfer via electromagnetic waves, related t T^4 |

conduction | thermal energy transfer via molecular collisions - requires contact |

PV work | W = P*deltaV (constant pressure)` |

1st law of thermodynamics | energy of the system and surroundings is always conserved, any energy change must equal heat flow into system plus the work delta(E) = q + w (work on the system is positive) |

2nd law of thermodynamics | heat cannot be changed completely into work in a cyclical process entropy of isolated system will never decrease |

carnot efficiency | e = 1 - Tc/Th |

internal energy | collectve energy of molecules measured on a microscopic scale, often referred to as heat, thermal energy, state function |

zeroth law of thermodynamics | two bodies in thermal equilibrium share a thermodynamic property - which is a state function -- TEMPERATURE EXISTS |

KEavg = | =3/2*kT where k is Boltzman constant |

enthalpy | manmade property that accounts for extra capacity to to PV work, defined as H = U + PV, not conserved like energy, not constant (of the universe), state function |

change in enthalpy at constant pressure | delta(H) = delta(U) + P*delta(V) |

standard enthalpy of formation | change in enthalpy for rxn that creates 1 mole of a cmpd from raw elements in their standard state |

if gas is not part of the rxn, the enthalpy change is... | equal to the heat, which in the absense of work is equal to a change in energy |

heat of rxn | delta(Hrxn) = delta(Hf of products) - delta(Hf of reactants) |

Hess' law | when you add rxns, you can add their enthalpies; also, forward rxn = neg of reverse rxn |

exothermic rxns have a positive or negative enthalpy | negative |

endothermic have a positive or negative enthalpy | postive |

if gas is not part of the rxn, the enthalpy change is... | equal to the heat, which in the absense of work is equal to a change in energy |

heat of rxn | delta(Hrxn) = delta(Hf of products) - delta(Hf of reactants) |

Hess' law | when you add rxns, you can add their enthalpies; also, forward rxn = neg of reverse rxn |

exothermic rxns have a positive or negative enthalpy | negative |

endothermic have a positive or negative enthalpy | postive |

if gas is not part of the rxn, the enthalpy change is... | equal to the heat, which in the absense of work is equal to a change in energy |

heat of rxn | delta(Hrxn) = delta(Hf of products) - delta(Hf of reactants) |

Hess' law | when you add rxns, you can add their enthalpies; also, forward rxn = neg of reverse rxn |

exothermic rxns have a positive or negative enthalpy | negative |

endothermic have a positive or negative enthalpy | postive |

if gas is not part of the rxn, the enthalpy change is... | equal to the heat, which in the absense of work is equal to a change in energy |

heat of rxn | delta(Hrxn) = delta(Hf of products) - delta(Hf of reactants) |

Hess' law | when you add rxns, you can add their enthalpies; also, forward rxn = neg of reverse rxn |

exothermic rxns have a positive or negative enthalpy | negative |

endothermic rxns have a positive or negative enthalpy | positive |

entropy | nature's tendency to create the most probable situation that can occur w/in a situation, state f(x), extensivy property (increases w/ amt of substance) |

delta(Suniverse) | >=0 = delta(Ssystem) + delta(Ssurroundings) |

entropy of system can decrease only if | at the same time, the entropy of the surroundings increase by a greater or equal magnitude |

ideal reactions create how much entropy change? | zero - meaning they are reversible |

if a rxn is unfavorable in terms of enthalpy, but increases entropy, will the rxn occur? | yes, entropy is the driving force that dictates whether or not it will proceed |

3rd law of thermodynamics | assigns by convention a zero entropy value to any pure substance at absolute zero and in internal equilibrium |

units of entropy? | J/K |

change in entropy related to heat eqn | delta(S) = dqrev/T where dqrev is the infinitesimal change in heat per kelvin |

Gibb's free energy | delta(G) = delta(H) - T*delta(S) (all of the system not surroundings), extensive property, state function, represents maximum non-PV work available from rxn |

when delta(G) is negative… | the rxn is spontaneous |

with +delta(H) and -delta(S), delta(G) will be.. | positive |

with -delta(H) and +delta(S), delta(G) will be… | negative |

what is value of gibb's free energy at equilibrium? | zero |

when both enthalpy and entropy are the same sign, free energy will be.. | positive or negative, therefore spontaneity of rxn will depend on the temperature |