06 Entropy

# 06 Entropy - Economic Value of Gasoline Last time we...

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1 1 Economic Value of Gasoline Last time we obtained -5080 kJ/mol for the enthalpy of combustion of gasoline (iso- octane). And 22.80 mol/gal. We now pay \$2.00/gal. Determine the economic value of gasoline in MJ/\$) from these data. M = mega = 10 6 Report 2 sig figs ## 2 Economic Value of Gasoline Last time we obtained -5080 kJ/mol for the enthalpy of combustion of gasoline (iso- octane). And 22.80 mol/gal. We now pay \$2.00/gal. Determine the economic value of gasoline in MJ/\$) from these data. M = mega = 10 6 Report 2 sig figs ## kJ/\$ 57,900 \$2.00 gal 1 gal mol 80 . 22 mol kJ 5080

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2 3 Rudolf Clausius German Physicist 1822 - 1888 Energy, Enthalpy, & Entropy These words come from the Greek. Energy means to put into work . Enthalpy means to put into heat . Entropy means to put into transformation . Invented by Clausius who was studying the transformation of heat into work. 4 Why are some processes spontaneous? Sugar and salt dissolve in water. Water freezes in the freezer. Ice melts on the countertop. Water and ice are in equilibrium at 273 K. Every process has a preferred direction, which is called the spontaneous direction. A spontaneous process occurs on its own accord unless restrained in some way. Note: spontaneous does not mean fast.
3 5 Some chemical reactions are spontaneous, and others are not! Baking powder + vinegar carbon dioxide + water Spontaneous, try this at home! Hydrogen + oxygen water Explodes spontaneously if started by tiny spark Don’t try this at home! Nitrogen + oxygen nitrogen oxides Won’t explode spontaneously, even if started by a bolt of lightening! 6 Maybe only exothermic reactions are spontaneous? Energy is transferred out of the system so the energy of the system goes down. Just like a car rolls down a hill spontaneously because a force is acting on it and the potential energy decreases.

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06 Entropy - Economic Value of Gasoline Last time we...

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