Quality vs. Quantity of Energy: Energy & Our World

When energy is used to do work, the quality (ease of use) is lowered 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

CO2 (and H2O(g)) in the atmosphere contribute to the greenhouse effect The burning of plants and fossil fuels releases CO2 into the atmosphere CO2 (and H2O(g)) in the atmosphere contribute to the greenhouse effect 30% of sun’s energy reflected back to outer space. Remaining 70% passes atmosphere to the earth’s surface. Some of the energy Is absorbed by plants for photosynthesis and some by the oceans to evaporate water, but most of it is absorbed by the earth’s surface. This is then radiated back as infrared radiation, or heat radiation. The atmosphere blocks the radiant energy from going to outer space, but instead traps some of the heat and then radiates it back to the earth’s surface. It traps the heat and makes the temperature of our earth higher. If you aren’t sure how water works into this equation, think of being in FL in the middle of the summer: sticky and HOT!

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 Reactions 1. energy spread 2. 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 Energy spread: Wood + O2  CO2 + H2O + ashes + energy but ashes will never absorb heat and turn back into wood… the spread of energy means that energy goes from an area of high concentration and disperses as much as possible in the surroundings by radiating out. Spread of matter: (demo with air freshener). Let’s agree that air freshener is a form of matter. It will diffuse when I spray it.

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?

Which has greater entropy?

“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…