Thermochemistry Flashcards
thermochemistry
study of the change of energy that takes place when a reaction return
endothermic reactions
decrease in temperature, heat reaction is positive
intrinsic energy
potential energy, bonds energy
activation energy
the minimum energy required for a reaction to take place
enthalpy
capacity to release heat
entropy
measure of disorder in a system
exothermic reactions
give off energy and are associated with an increase in temperature
translational
movement of molecules in their (liquids and gasses)
rotational
rolling and flipping of molecules (liquids and gasses)
collision molecular theory
no collision, no reaction
vibratoinal
back and forth movement of molecules with respect to each other (solids, liquids and gasses)
potential energy
stored in chemical bonds
law of conservation of energy
energy is neither created nor destroyed under normal physical conditions, as molecular potential energy increases, kinetic energy decreases and visa-versa
calorie (cal)
the amount of energy required to raise the temperature of one gram of water by one degree Celsius
Kilocalorie (Kcal)
1 Kcal = 1000. calories
Kilowatt hour (Kwh)
1 Kwh = 860 Kcal
Joule (J)
1 cal = 4.184 J, 1 Kcal = 4.184 J
heat energies in endothermic reactions
require heat; vaporization, fusion (melting), decomposition
heat energies in exothermic reactions
release heat; condensation, solidification (freezing), synthesis, combustion
enthalpy (△H)
represents the change in heat for any reaction: △Hrxn = ∑Hproducts - ∑Hreactants
Hess’s Law
if you can combine the half reactions, you can combine the enthalpies
specific heat (Cp)
energy required to raise the temperature of one gram of any substance by one degree celsius
specific heat of H20(s)
0.500 cal/g℃
specific heat of H20(l)
1.00 cal/g℃
specific heat of H20(g)
0.500 cal/g℃
heat of fusion (△Hfus)
energy required to melt one gram of any substance
heat of fusion for water
80.0 cal/g
heat of vaporization (△Hvap)
energy required ot vaporize one gram of any substance
heat of vaporization for water
540.0 cal/g
equations for calorimetry
Q = m x △T x Cp Q = m x △Hfus Q = m x △Hvap
entropy (△S)
the change in disorder, chaos, or randomness for a substance or reaction
△S>0, increase in disorder
△S<0, decrease in disorder
△S = ∑△Sproducts - ∑△Sreactants
gibbs free energy (△G)
the chemical potential of a substance, predicts reaction spontaneity
△G>0, reaction is non-spontaneous
△G<0, the reaction is spontaneous
△G = △H - T△S
