chps 12 + 23 test Flashcards
heat
the energy that flows from one object to another due to a difference in temperature (warmer to cooler)
enthalpy
the heat content of a system at a constant pressure (enthalpy=heat)
why do chemical reactions involve heat?
because bond breaking requires energy and bond forming releases energy, and heat is energy
thermochemistry
the study of the heat changes in chemical reactions
exothermic reactions
overall, heat is released
endothermic reactions
overall, heat is required (absorbed)
thermochemical reactions/equations
includes the heat lost or gained (in the equation)
signs of ΔH
- = exothermic \+ = endothermic
hess’s law
if a series of reactions are added together, the enthalpy change for the net reaction is the sum of the enthalpy changes of the individual steps
1st law of thermodynamics
there is a tendency in nature for reactions to occur which lead to a lower energy level (or conservation of energy)
less energy means more stability
a negative ΔH is favored y by nature
2nd law of thermodynamics
there is a tendency in nature for processes to occur which lead to a greater entropy (or things happen in nature that lead to more disorder)
a positive ΔS means greater entropy
a reaction with a positive ΔS should be spontaneous
spontaneous
a spontaneous reaction is one that occurs without any continuous outside intervention
entropy
disorder
signs of ΔS
- = less entropy (more stability and is favored by nature), nonspontaneous \+ = greater entropy, spontaneous
gibbs free energy
is the first two laws disagree on spontaneity, the temperature must be know (because the temperature is the dominant factor in determining spontaneity)
