Quality vs. Quantity of Energy:Energy & Our World

• Energy is conserved:• The quantity of energy in the universe is

constant!• The quality of that energy, however,

changes!

• When energy is used to do work, the quality (ease of use) is lowered• Ex.: car driving• The quality of energy is changed from concentrated to s p r e a d o u t

“HEAT DEATH” of the Universe

• Someday… far, far in the future, all energy will be evenly spread throughout the universe and everything will be at the same temperature

• It will not be possible to do any work, so the universe will be dead!

• But why?

Energy and Our World• Most of the energy for our world and

society comes from woody plants, coal, petroleum, and natural gas

• The energy of these originally came from the sun…

• Plants store energy from the sun by the process of photosynthesis

• That stored energy can be released by burning the plants directly or by burning their the decay products that have been converted over millions of years into fossil fuels

• The burning of plants and fossil fuels releases CO2 into the atmosphere

• CO2 (and H2O(g)) in the atmosphere contribute to the greenhouse effect

• The atmosphere is like a blanket around the Earth…

• It is thought that the increasing amount of CO2 (and other gases) in the atmosphere may have an effect on the climate • Global warming?

• The increase in CO2 in the atmosphere in recent years is quite dramatic, but it’s exact relationship to the climate is not known

Energy as a Driving Force• Imagine a log burning in your fireplace…log + O2 CO2 + H2O + ashes + energy

• Why does the reverse reaction never happen????

Two Driving Forces of Chemical Reactions1. energy spread2. matter spread

• Energy spread: concentrated energy is dispersed widely• Occurs in every exothermic process

• Matter spread: molecules of a substance spread out and occupy a larger volume

A process is favored if it involves energy spread and/or matter spread!!

Entropy• Entropy: a function invented to keep track of

the natural tendency for components of the universe to become disordered• Symbolized by “S”• Measure of disorder or randomness• As disorder increases, entropy increases, and S value

increases

• Which has a lower entropy, ice or liquid water?

• “Energy spread” causes faster random motions of molecules in the surroundings (KE of molecules increases)

• “Matter spread” causes molecules to occupy a larger volume and become intermixed with other molecules• Both of these processes lead to greater entropy (disorder)

in the universe

Second Law of Thermodynamics

• The entropy of the universe is always increasing!• A process is spontaneous only if the

entropy of the universe increases as a result of the process• Spontaneous process: occurs in nature

without outside intervention (“happens on its own”)

Analogy

• Your bedroom…