What is difference in a chemical and physical change?
A physical change in a substance doesn't change what the substance is. In a chemical reaction a new substance is formed and energy is either given off or absorbed.

Production of light
Natural resources of light include our sun and other stars,where the source of energy is nuclear energy (recall that the moon does not produce light ,but merely reflects sunlight),lighting,where the source is electrical,and fire,where energy source is chemical. For eons of human history,these were the only source of light available until people discovered burning natural oils and developed candles in the relative recent past

Example of light
You see a gloomy porch and then a brilliant porch.

Production of precipitate
The precipitate forms because the solid (AgCl) is true for all precipitate-the solids are in solution. Precipitate reaction occur all around us.

Example of production of precipitate
Sometimes the pipe sin our homes get clogged because precipitates of magnesium and calcium oxide have deposited themselves within the pipe. This can happen with "hard" water.

Production of gas
Natural gas rises up the well using natural energy. It is produced in America,Europe,Africa,and other regions.

EXAMPLE OF PRODUCTION OF GAS:USED FOR-

• Natural gas meets 28 percent of U.S. energy demand (as of 2012)
• Natural gas now heats 51 percent of U.S. household. It also cools many homes and provides fuel for cooking
• Because natural gas burns cleaner than gasoline or diesel,many companies and municipalities are deploying fleets of natural gas -powered cars,trucks and buses to reduce emissions. There are approximately 142,000 natural gas vehicles operating on American roads.

Color change
Color conveys meaning. We use it to define our sensory experience, to describe objects,express emotion,and evoke a response. It is descriptive beyond what we see. It's no wonder that color plays a large role in video production and careful thought goes into crafting the color palettes on screen.

Example of Color Change
When an ice cube melts for example, it becomes liquid water.

Change in Temperture
You can usually calculate the change in temperature by doing a simple subtraction problem--just subtract the original temperature from the new temperature to see how much it changed. The problem gets more complicated,however,if the two temperature values are in different units.

Example of production of temperature
For example,how you figure out the change in temperature if you know that the morning it was 41 degrees Fahrenheit,but in the afternoon it was 29 Celsius? Actually ,29 degrees Celsius is the warmer than 41 degrees Fahrenheit ,and you can figure out by exactly how much by doing a few simple calculation.